Surveyor Lunar Lander 1966-1968 (Boeing - NASA)

LL 0 > i (PAGESI (COVE) / BSR--O3 N 2 (NASA?% J OR rmx OR AD N U M B E R ) 8GC/ 8 (CATYZORY) 3 / , Volume V GPO PRICE $ - SYSTEM EVALUATION CFSTI PRICE(S) $ Microfiche (MF) ff 653 July65 T ! d / S Y S T E l S DIVISlON SU RVEY0R L U N A R R O V I N G VEHICLE, PHASE I BSR-903 F I N A L TECHNICAL REPORT SUBMITTED TO JET P R O P U L S I O N L A B O R A T O R Y C A L I F O R N I A INSTITUTE O F T E C H N O L O G Y J P L CONTRACT 950656 VOLUME V SYSTEM E V A L U A T I O N APRIL 1964 ~ " d y s v TEMS s DIVlSlON BSR 9 0 3 . .---e-- I ii , , - 'SURVEYOR L U N A R R O V I N G VEHICLE, PHASE I -..-" -I _ - - / f BSR-903 F I N A L TECHNICAL REPORT SUBMITTED I TO 1 JET P R O P U L S I O N L A B O R A T O R Y C A L I F O R N I A INSTITUTE O F T E C H N O L O G Y CONTRACT 950656 JPL VOLUME V SYSTEM E V A L U A T I O N I I I i A P R I L 1964 I . .I-..._ --..- BSR 9 0 3 ii BSR 903 FOREWORD As p a r t of the continuing p r o g r a m of unmanned exploration of space, and to i n c r e a s e the effectiveness of the manned space p r o g r a m f o r exploring the moon, the J e t Propulsion Laboratory of the California Institute of Technology issued six-month study contracts to investigate the feasibility of a s m a l l , unmanned, lightweight, r e m o t e l y controlled roving vehicle t o be incorporated in the s u r v e y o r spacecraft to extend i t s data-gathering capabilities on the lunar surface. Specifically, the study p r o g r a m was to d e t e r m i n e the feasibility of a 100-lb Surveyor Lunar Roving Vehicle (SLRV) s y s t e m i n gathering sufficient scientific information by surveying the lunar s u r f a c e n e a r the Surveyor spacecraft landing point to c e r t i f y the a r e a , i n t e r m s of specific h a z a r d s , as a potential Apollo LEM landing site. This F i n a l Technical Report, submitted in five volumes, p r e s e n t s the r e s u l t s and conclusions of the study p r o g r a m conducted by The Bendix Corporation under JPL C o n t r a c t No. 950656. The volumes a r e organized to c o r r e s p o n d to the specific objectives of the p r o g r a m : to conduct an analysis, to g e n e r a t e a p r e l i m i n a r y design, and to f a b r i c a t e and d e m o n s t r a t e a n engin e e r i n g t e s t model in support of the o v e r - a l l p r o g r a m objectives. The r e s u l t s of Bendix's study show that the SLRV concept i s not only f e a s i b l e , but can make substantial contributions to the unmanned exploration The SLRV c h a r of the moon i n support of the manned Apollo p r o g r a m . a c t e r i s t i c s , the p r o b l e m s , and the initial trade-offs have been d e t e r m i n e d i n sufficient detail to p e r m i t the definition of specific objectives and c r i t e r i a f o r a follow-on development program. P r o g r a m conclusions and r e c o m mendations a r e included i n Volume V. iii BSR 903 LIST OF VOLUMES - PROGRAM SUMMARY VOLUME II - MISSION AND SYSTEM STUDIES VOLUME 111 - PRELIMINARY DESIGN AND VOLUME I SYSTEM DESCRl PTI ON Book 1 - System Description and Performance Character istics Book 2 - Validation of Preliminary Design VOLUME IV - RELIABILITY VOLUME V - SYSTEM EVALUATION THEDOCUMENTYOUAREREADING IS INDICATED BY THE ARROW BSR 903 I 1. 2. TABLE O F CONTENTS Page INTRODUCTION MISSION EVALUATION 2. 1 1- 1 2- 1 2- 1 2-2 2-3 2-6 2-6 2-7 2-7 2- 7 2-8 2 - 10 2- 10 2-11 2-11 2- 12 3-1 3-1 EFFECTIVENESS DEFINITION 2. 2. 2. 2. 1. 1 Defined Mission T e r m 1. 2 c o s t 1. 3 Probability of Success 1 . 4 Effectiveness Level 2.2 ANALYSIS O F COMPETITIVE PROGRAMS 2. 2. 2. 2. 2. 2. 1 2. 2 2. 3 2.4 2.5 Apollo LEM Lunar Orbiting Satellite (LOS) Surveyor A Apollo B Second Generation LRV 2.3 2.4 2.5 3. SLRV PROGRAM PROBABILITY O F SUCCESS SLRV SINGLE LAUNCH PROBABILITY O F SUCCESS ROVING VEHICLE PROBABILITY O F SUCCESS EVALUATION O F 100-LB SYSTEM 3.1 EVALUATION SIMULATION 3. 1. 1 Evaluation Approach 3. 1. 2 Simulation Details 3-1 3-5 3-33 3-33 3-35 3-39 3-42 3-48 3-48 3-51 3 -60 3. 2 SIMULATION RESULTS 3. 3. 3. 3. 2. 1 2. 2 2. 3 2.4 Probability of Mission Success Mission Duration and Distance Reliability Effects Adaptive Mission 3.3 ROVING PATTERN STRATEGY 3.3. 1 P r o g r a m Strategy 3. 3. 2 Mission Strategy 3. 3. 3 Example of Mission Strategy V . BSR 903 . TABLE O F CONTENTS (CONT) Page 4. EVALUATION O F HEAVIER VEHICLES 4. 1 4. 2 4-1 4-1 4-2 4-2 4-6 4-6 4-6 4-6 5-1 5-6 5-7 5-7 5-7 5 -7 5-7 5-11 5-11 5-11 SYSTEM DESCRIPTIONS PROBABILITY O F MISSION SUCCESS 4. 2. 1 Basic Mission 4. 2. 2 Adaptive Mission 4. 3 MISSION DURATION 4 . 3. 1 B a s i c Mission 4. 3. 2 Adaptive Mission 5. ENGINEERING TEST MODEL TEST RESULTS 5.1 5.2 TEST COURSE DESCRIPTION TEST RESULTS 5. 5. 5. 5. 5. 5. 5. 2. 1 2. 2 2. 3 2.4 2. 5 2. 6 2. 7 Mobility Step T e s t Knife Edge T e s t Crevice Test T r a c k Abort T e s t Random Obstacle T e s t P o w e r Limitations 5.3 E T M MOBILITY EXTRAPOLATION 5-11 BSR 903 LIST O F ILLUSTRATIONS Figure Title Effective C o s t v s T i m e Before Apollo Launch Single Landing Point Diameter v s L E M Probability of Translating to Landing Point Simulation Concept Relationship Between PTs and Diameter of Verified Site Simulation Flow C h a r t Simulation Details Definition of I r r e g u l a r i t y Models Definition of Slope Models Definition of Bearing Strength Models Reliability Input Opera ti onal C ons t r a i n t s Detour F a c t o r , F Random T e r r a i n Map, 2 0 % Bad Random T e r r a i n Map, 50% Bad Effect of Surface Model on Probability of S u c c e s s , Models 1 and 8 a n d Composite Model Effect of S u r f a c e Model on Probability of Success, Models 1, 2, 3, and 4 Effect of S u r f a c e Model on Probability of S u c c e s s , Models 1, 5, 6, and 7 Effect of S u r f a c e Model on Mission Duration and Di s tanc e Effect of Reliability on Probability of S u c c e s s Effect of P a r t i a l F a i l u r e s on Probability of S u c c e s s Effect of P a r t i a l F a i l u r e of R F Ranging and T r a c t i o Drive Mechanism a t S t a r t of Mission on Probability of Success Effect of Partial F a i l u r e of Directional Antenna a n d TV Azimuth P a n at S t a r t of Mission on Probability of S u c c e s s Page 2-5 2.1-1 2.2-1 3-1 3-2 3-3 3 -4 3-5 3 -6 3-7 3-8 3-9 3- 10 3-11 3-12 3-13 3-14 3-15 3- 16 3-17 3-18 3-19 2-9 3-3 3- 4 3 -6 3-713-8 3 - 13 3- 14 3- 15 3-22 3-23 3-26 3-28 3-29 3-34 3-36 3-37 3-38 3 -40 3-41 3-43 3-20 3 -44 V vii . c BSR 903 , LIST O F ILLUSTRATIONS (CONT) Figure 3-21 Title Effect of P a r t i a l F a i l u r e a t S t a r t of Mission on Probability of S u c c e s s , TV r e s t r i c t e d t o l o o Field of View, 50% L o s s of Resolution Probability of S u c c e s s f o r Adaptive Mission Comparison of Basic a n d Adaptive Mission S u c c e s s Effect of Surface Model on Mission Duration for Adaptive Mission Definition of Mission Strategy A r e a Sampling i n T e r r a i n Containing L a r g e Unacceptable A r e a s Rules of Strategy LEM Aim Point Adjustment P a t t e r n R e loc a t i on Example of Strategy Application Probability of Success - Heavier Vehicles Probability of S u c c e s s for Heavier Vehicles, Basic Mission Effect of SLRV I r r e g u l a r i t y Capability Probability of S u c c e s s - Heavier Vehicles Probability of S u c c e s s f o r Heavier Vehicles, Adaptive Mission Mission Duration for H e a v i e r Vehicles, Basic Mission Mission Duration for Heavier Vehicles, Adaptive Mis s ion Mission Duration for 110-lb S y s t e m Mission Duration for 120-lb System Mission Duration f o r 130-lb S y s t e m Mission Duration for 140-lb S y s t e m Mission Duration for 150-lb S y s t e m Side View, E T M F r o n t View, E T M E T M Console Assembly E T M T e s t R e s u l t s of Step-Climbing Capability E T M C r e v i c e - C r o s s i n g T e s t R e s u l t s on Roofing P a p e r Surface F o u r - T r a c k Vehicle Mobility Extrapolation Page - 3-22 3-23 3 -24 3 -25 3-26 3-27 3-28 3-29 3-30 4- 1 4-2 4-3 4 -4 4-5 4-6 4-7 4-8 4-9 4-10 4-11 4-12 5-1 5-2 5-3 5 -4 5-5 5 -6 3 -45 3 -46 3 -47 3 -49 3-50 3-53 3-56 3-58 3-59 3-62 4-3 4-4 4-5 4-7 4-8 4-9 4 - 10 4 - 12 4- 13 4 - 14 4 - 15 4-16 5-2 5-3 5-5 5-8 5-9 5-13 viii V BSR 903 LIST OF TABLES i Table Title Surface Model S u m m a r y Summary of Heavier Vehicles Soil P a r a m e t e r s Crevice Tests Page - 3-1 4- 1 5-1 5-2 3 - 17 4- 1 5 -6 5- 10 ix BSR 903 SECTION 1 IMTRODUC TION This volume of the F i n a l Technical Report p r e s e n t s the r e s u l t s of the P h a s e I SLRV study p r o g r a m in accordance with the portion of A r t i c l e 1, Section (a) ( 1 ) (iv) of the Statement of Work of J P L C o n t r a c t No. 950656, Modification No. 1, which s t a t e s : the probability that a single roving vehicle s y s t e m w i l l successfully m e e t the mission objectives specified in E P D No. 98 f o r the s y s t e m , given that the performance of the launching vehicle and the Surveyor s p a c e c r a f t a r e within the expected t o l e r a n c e . In p e r f o r m a n c e t h e r e o f , the Contractor shall: Analyze the probabilities of meeting p a r t i a l objectives throughout the roving vehicle mission operational sequence. F u r n i s h a plan f o r operating the roving vehicle on the l u n a r s u r f a c e . This plan s h a l l include the s t r a t e g y for choosing between v a r i o u s roving patterns and c r i t e r i a f o r changing the p a t t e r n depending on the d a t a r e t u r n e d and the possibility of p a r t i a l f a i l u r e . The plan s h a l l be coordinated with DSIF capability. D e t e r m i n e the probability of the roving vehicle certifying the safety of a landing s i t e f o r the Apollo LEM as a function of the n a t u r e of the l u n a r surface. This study is to take into consideration the mechanical reliability of the r o v e r and the uncertainty in the knowledge of the s u r f a c e due to finite sampling, i m p e r f e c t m e a s u r e m e n t s etc. The c r i t e r i a for certification is given in EPD-98. I ' In addition, a n evaluation of the p e r f o r m a n c e of SLRV s y s t e m s f o r g r o s s weights i n e x c e s s of 100 lb is given, a s well as the r e s u l t s of t e s t s conducted during the study p r o g r a m on a n engineering t e s t model*designed and f a b r i c a t e d to d e m o n s t r a t e mobility and maneuverability capabilities and l i m i t a t i o n s of the 100-lb design. ". . . calculate V 1- 1 SECTION 2 MISSION EVALUATION T h i s section p r e s e n t s a n evaluation of the S L R V Mission in support of the Apollo p r o g r a m , r e l a t i v e to s i m i l a r m i s s i o n s of other existing p r o g r a m s . The p r i m a r y objective of this evaluation is the e s t a b l i s h m e n t of the r e q u i r e d S L R V s y s t e m probability of s u c c e s s (P ) f o r t h e site v e r i fication m i s s i o n by c o m p a r i s o n with the r e l a t i v e c a p a b a i t y of o t h e r s y s t e m s to accomplish the s a m e objectives. Specifically, the m i s s i o n of s i t e verification h a s been defined in t e r m s of the d a t a to be collected on the bearing s t r e n g t h of the l u n a r s o i l , s m a l l s c a l e topography (in the region of 2 5 cm t o 1 m e t e r ) , and slope in the potential s i t e a r e a . 2. 1 EFFECTIVENESS DEFINITION The a p p r o a c h to m i s s i o n evaluation is to e s t a b l i s h an effectiveness c r i t e r i a (E) such that ( 2 . 1-1) where G = the m i s s i o n defined above P P = t h e probability of a given d i a g r a m accomplishing this m i s s i o n P C r = the c o s t of accomplishing the m i s s i o n in t e r m s of t i m e and d o l l a r s . Since all existing l u n a r - o r i e n t e d s y s t e m s such a s Surveyor A , LOS, e t c . , can provide some m e a s u r e of Gp for some established o r p r e d i c t e d c o s t , and at some period of t i m e p r i o r to the manned landing m i s s i o n , then E , the c o m p a r i s o n v a r i a b l e , m a y be established f o r all existing s y s t e m s . V 2-1 BSR 903 Assuming that an i n c r e a s e in the value of E by a f a c t o r of 4 over other s y s t e m s is a c r i t e r i a f o r continued development of the SLRV P r o g r a m , then f o u r times the maximum effectiveness determined f o r any of the other s y s t e m s would be used in Equation (2. 1-1) to d e t e r m i n e the value of P P r e q u i r e d f o r SLRV. The comparison to SLRV m a y be made for each other p r o g r a m s e p a r a t e l y o r against all other p r o g r a m s in combination. The following sections develop the complete definitions of the m i s s i o n (Gp), the effectiveness c r i t e r i a ( E ) , and the c o s t factor (C). This is followed by the derivation of E f o r each of the other competing s y s t e m s . The section will be concluded with the calculation of the r e q u i r e d effectiven e s s ( E ) and, hence, Ps for SLRV, where ps is one t e r m in the p r o g r a m probability (P,) defined above. 2. 1 . 1 Defined Mission T e r m The m i s s i o n t e r m , Gp, is defined to include the type, quantity, and quality of data n e c e s s a r y to c e r t i f y a landing s i t e f o r Apollo with a confidence of 99%. The data r e q u i r e d a r e defined a s follows: 1. Determination of effective p r o t u b e r a n c e s of 50 c m o r g r e a t e r where an effective protuberance is defined a s the s u r f a c e a n d / o r subsurface relief within a horizontal distance of approximately 10 m e t e r s which might c a u s e the bottoming a n d / o r tilting of the LEM. Effective protuberances m a y r e s u l t f r o m single objects o r complex combinations of heights, d e p r e s s i o n s , and s u r f a c e sinkages. The maximum r e l i e f contributed by a single p r o t u b e r ance o r combination of p r o t u b e r a n c e s and d e p r e s s i o n s m a y range f r o m 20 to 50 c m . The determination of effective s l o p e s of 12 o r g r e a t e r where a n effective slope is defined as the g e n e r a l s u r f a c e slope over a n a r e a too l a r g e f o r the L E M t o s t r a d d l e , plus the combined effects of superimposed heights, d e p r e s s i o n s , and s u r f a c e sinkage. 0 2. V BSR 9 0 3 3. The determination of surface bearing strengths which will p e r m i t sinkage of no greater than 10 c m f o r a 1. 0 - p s i s t a t i c load o r sinkage no g r e a t e r than 30 c m f o r a dynamic load of 12 p s i at an impact velocity of 3 m e t e r s p e r second. T h e s e data m u s t be collected i n sufficient quantity and quality to e n s u r e with 90% confidence that 95% of a 3200-meter d i a m e t e r s i t e is acceptable and that 7070 of t h i s s i t e i s acceptable with 99% confidence. Since a s i t e which s a t i s f i e s t h e s e requirements will provide a probability of a successful LEM landing (PL)of 0 . 9 9 , t h i s value is used a s the maximum value f o r G p . The m e a s u r e m e n t s of s o i l , slope, and protuberance c h a r a c t e r i s t i c s a r e considered of equal importance to the probability of a successful L E M landing f o r lack of any o t h e r justifiable weighting. It h a s t h e r e f o r e been a s s u m e d that the determination of a n y two of the t h r e e c h a r a c t e r i s t i c s satisfying the confidence levels noted above will r e s u l t in a value f o r G p of 0 . 6 6 and that the determination of a n y one of the t h r e e c h a r a c t e r i s t i c s defined above will r e s u l t in a value of G p equal t o 0. 33. I 2.1.2 cost In establishing a relative c o s t figure, two m e a s u r e s of c o s t a r e c o n s i d e r e d significant. First is the development and operational c o s t of the p r o g r a m s t o be considered f o r evaluation, and second is a m e a s u r e of the potential cost i n c u r r e d caused by a slippage in the Apollo mannedlanding launch date - - i f it is determined that the lunar s u r f a c e c h a r a c t e r i s t i c s a r e such that a n unreasonably low confidence in landing exists with the c u r r e n t Apollo design. It m u s t be a s s u m e d that confidence i n the ability of the Apollo LEM t o land successfully is equal to the confidence in the knowledge of the acceptability of the landing s i t e . F o r example, at the p r e s e n t t i m e , confidence in the ability of the LEM to land on the moon m u s t be considered to b e quite low, since t h e r e i s no knowledge of the s m a l l - s c a l e t e r r a i n c h a r a c t e r i s t i c s of any portion of the l u n a r s u r f a c e . T h e r e f o r e , t h e r e is a s m u c h probability that no acceptable landing s i t e e x i s t s a s t h e r e is the probability that an acceptable landing site does exist. .. V 2-3 BSR 9 0 3 To explore this approach to the m e a s u r e of cost, consider the following. If no p r o g r a m p r i o r to the launch of the manned-landing m i s s i o n is successful, then even i f the Apollo LEM had the capability t o m e a s u r e the t e r r a i n c h a r a c t e r i s t i c s as defined in Section 2. 1. 1 above, confidence in the ability to make a successful landing m u s t still be cons i d e r e d low since t h e r e is no p r i o r knowledge that such a landing s i t e e x i s t s . On the other hand, if one o r m o r e l u n a r exploratory s y s t e m s is s u c c e s s f u l s e v e r a l y e a r s p r i o r to the manned landing, then a high d e g r e e of confidence will e x i s t in the findings of that s y s t e m . If the s y s t e m data indicate that a l a r g e percentage of the moon's s u r f a c e i s acceptable in t e r m s of the Apollo LEM landing c h a r a c t e r i s t i c s , then a high d e g r e e of confidence in a s u c c e s s f u l LEM landing e x i s t s . In the event the data r e t u r n e d by t h i s e a r l y explorat o r y system indicates that only a s m a l l percentage of the actual s u r f a c e is acceptable to Apollo, then sufficient t i m e would exist t o take s e v e r a l c o u r s e s of action. Examples would be improving the maneuvering capability of LEM o r modifying the LEM landing s y s t e m t o accommodate the m o r e rugged t e r r a i n . In e i t h e r c a s e , the delay in the launch date of the man-landing p r o g r a m would be m i n i m a l , and the additional c o s t would be s m a l l compared t o the c o s t of delaying the e n t i r e Apollo p r o g r a m , which would occur if this information w e r e not obtained until the t i m e of the f i r s t manned landing attempt. F o r the purpose of evaluation, it h a s been a s s u m e d that i t would r e q u i r e approximately one y e a r to modify the Apollo s y s t e m e i t h e r to improve its navigation capability o r to improve the landing g e a r , and that the cost value of slippage in the Apollo launch date is one billion d o l l a r s / y e a r . Therefore, the m e a s u r e of cost in evaluating any s y s t e m will include not only the development and operational c o s t , including the total n u m b e r of flights postulated f o r that s y s t e m , but a l s o a n "effective" c o s t t e r m reflecting the amount of t i m e p r i o r to the f i r s t manned landing that the s y s t e m completes i t s m i s s i o n . F i g u r e 2 . 1 - 1 i l l u s t r a t e s the c o s t relationship which is also e x p r e s s e d below. (2.1-2) V BSR 903 i I /fl Ii. ’ G Figure 2. 1 - 1 Effective Cost vs Time Before Apollo Launch V 2-5 BSR 903 where: C, = development and operational cost of p r o g r a m CA = cost of one Apollo manned launch tBL = t i m e of launch before Apollo launch ( y e a r s ) 5 1 Based upon Equation 2. 1-2, it m a y be s e e n , f o r example, that the "cost" t e r m (when determining the effectiveness of the Apollo LEM to find i t s own landing s i t e without p r i o r exploration) would include the normalized development cost f a c t o r , which in this c a s e is unity, plus the normalized maximum i n c r e a s e caused by a o n e - y e a r delay of one billion d o l l a r s divided by the development cost of the Apollo p r o g r a m . Conversely, System X , which is developed and operational, s a y , m o r e than one y e a r p r i o r to the manned landing ( t g L = l . O ) , would have a s i t s cost t e r m i t s development and operational cost normalized t o the c o s t of Apollo without the addition of delay cost. This follows since the findings of t h i s p r o g r a m with r e s p e c t t o the acceptability of the l u n a r s u r f a c e , whether good o r bad, would be known in time to make the n e c e s s a r y modifications to Apollo without an appreciable c o s t i n c r e a s e . 2. 1. 3 Probability of Success Success probability involves two f a c t o r s : ( 1 ) the probability that the equipment does not fail (mechanical r e l i a b i l i t y ) , and ( 2 ) the probability that equipment p e r f o r m a n c e will be within the t o l e r a n c e s established f o r the design. 2. 1 . 4 Effectiveness Level The p r o g r a m s to be considered in t e r m s of t h e i r effectiveness f o r Apollo landing s i t e verification a r e : 1 . Surveyor Lunar Roving Vehicle 2. Surveyor A Lunar Orbiting Satellite 3. 4 . A manned Lunar O r b i t e r , t e r m e d Apollo B 5. Second Generation LRVs. BSR 903 2 . 2 ANALYSIS O F COMPETITIVE PROGRAMS 2. 2. 1 Apollo LEM In evaluating the Apollo L E M capability of verifying its own landing s i t e , it is to be expected that the LEM c r e w will have an adequate capability of s m a l l - s c a l e relief and slope detection, but not capability for s o i l bearing s t r e n g t h m e a s u r e m e n t . The m i s s i o n t e r m s in percentage a r e then GPOB I = 33 GpSL = 33 I I GpS = o The proability of s u c c e s s in detection of t h e s e h a z a r d s by the LEM will be a s s u m e d t o be unity, o r P = 1.0. P By definition, the t i m e before launch f o r LEM, tBL, = 0. T h e cost of one Apollo launch (development and operation) is e s t i mated to be $100,000,000. T h e r e f o r e , the effectivenss is calculated f r o m Equations 2. 1-1 and 2.1-2: (0 t 33 t 33)(1.0) = 6.0 . , V 2-7 BSR 903 Based on t e n launches, the LOS probability of s u c c e s s Pp = 1 . 0 . The data will be obtained at l e a s t one y e a r p r i o r to the f i r s t Apollo launch and t h e r e f o r e t = 1.0. BL The c o s t of the LOS p r o g r a m is e s t i m a t e d to be $100,000,000. T h e r e f o re , N E = ( 0 t 0 t 33)(1.0) = 33.0 fo . t lo8\ 2.2.3 Surveyor A F i g u r e 2. 2-1 shows that a 0 . 71 L E M landing s u c c e s s probability is a s s o c i a t e d with one 6 0 - m e t e r d i a m e t e r LEM landing point. Since t h i s i s approximately the limit of the Surveyor A ' s TV s u r v e y range, the following d a t a gathering capabilities c a n be calculated GPOB GPSL = 0 . 71 x 33 = 0 . 71 x 33 23.5 23. 5 . The confidence gained by bearing s t r e n g t h m e a s u r e m e n t s i n only one position is v e r y low and is a s s u m e d t o be 10% of the d e s i r e d value. The r e f o r e Gps = 0 . 1 x 33 = 3 . 3 . With seven o r m o r e flights, a high p r o g r a m probability of s u c c e s s will be obtained. If the single launch probability of s u c c e s s is 0. 5, then t h e p r o g r a m probability of s u c c e s s f o r s e v e n flights is 0 . 9 9 and will be a s s u m e d t o be unity. The Surveyor A p r o g r a m will be completed m o r e than one y e a r b e = l . 0. f o r e the first Apollo launching and, t h e r e f o r e , t BL Estimated cost of the p r o g r a m is $ 250,000,000. V BSR 903 Figure 2 . 2 - 1 Single Landing Point Diameter vs LE M Probability of Translating to Landing Point V 2-9 BSR 903 Therefore E = (3. 3 t 23. 5 t 23. 5)(1. 0 ) /2.5 x lo8 \ = 20.2 . 2. 2.4 Apollo B The Apollo B, taking high-resolution p i c t u r e s f r o m o r b i t , will have the full capability of s m a l l - s c a l e relief and slope detection r e q u i r e d for s i t e verification, but no capacity f o r s o i l bearing s t r e n g t h m e a s u r e m e n t . A p r o g r a m probability of s u c c e s s equal to that of other manned m i s s i o n s ( Z 1 . 0 ) will be a s s u m e d . The t i m e before Apollo launch is taken as 0. 5 y e a r , and the e s t i mated cost is $75,000, 000 f o r a single flight (development c o s t s a r e e s s e n t i a l l y accounted for in the normalized LEM c o s t ) . Then: E = [(. (0 t 33 t 33)(1.0) 5)lO 9 t ( 7 . 5 x 10 IO8 2. 2. 5 '-1 = 11.5 . Second Generation LRV A second generation LRV, i n a weight c l a s s requiring a l a r g e r launch vehicle than SLRV, would p o s s e s s a full capability f o r LEM landing s i t e verification in all t h r e e h a z a r d c l a s s e s . The single launch probability of s u c c e s s is taken to be 0. 5. Howe v e r , it i s a s s u m e d t h e r e will be two f l i g h t s , making the p r o g r a m probability of success 0 . 75. Since t h i s would be a new development p r o g r a m , it is a s s u m e d the data would not be received until 0. 5 y e a r b e f o r e the first Apollo launch. The estimated p r o g r a m cost i s $ 4 0 0 , 0 0 0 , 0 0 0 . 2-10 V The r efo r e E = ( l O O ) ( O . 75) = 8.4 c LO.1 1 0 ~ 5 t . (4x 1 0 ~ 1 1 108 '-l 2 . 3 SLRV PROGRAM PROBABILITY OF SUCCESS It h a s been stated that the SLRV must p o s s e s s an effectiveness four t i m e s a s g r e a t a s any of the competitive p r o g r a m s . It h a s been shown that the LOS has the highest effectiveness of the competitive p r o g r a m s (33.0). T h e r e f o r e , the SLRV program effectiveness m u s t be 132. The SLRV h a s a complete capacity f o r the LEM s i t e verification m i s s i o n (G = 1 . 0 ) . P F o r SLRV, t B L = 1. 0 , and the program c o s t is e s t i m a t e d a t $ 5 0 , 0 0 0 , 000. The expression f o r p r o g r a m probability of s u c c e s s is then 1 132 = I , ' L ) . . I lo8 o r , the r e q u i r e d p r o g r a m probability of s u c c e s s is 0. 66. 2.4 SLRV SINGLE LAUNCH PROBABILITY O F SUCCESS The relationship between the p r o g r a m probability of s u c c e s s and the single launch probability of s u c c e s s is P P = l(1- pssL In I I V 2-11 BSR 903 where p r o g r a m probability of s u c c e s s PSSL = probability of s u c c e s s of a single launch number of launches. F o r the SLRV, n i s taken t o be eight. (1 Therefore: - PS ) SL 8 = 1 - 0 . 6 6 = 0.34 F r o m which a r e q u i r e d single launch probability of s u c c e s s of 0. 13 is calculated. 2 . 5 ROVING VEHICLE PROBABILITY OF SUCCESS The single launch probability of s u c c e s s , pssL, is c o m p r i s e d of three terms: 1. Atlas-Centaur s u c c e s s probability Surveyor landing s u c c e s s probability Roving vehicle s u c c e s s probability. 2. 3. The Atlas-Centaur probability of s u c c e s s , estimated f o r the t i m e period when the SLRV will be operational, is 0. 7 . The s u c c e s s probability for Surveyor is a s s u m e d t o be 0. 5 . The refore 0. 13 = (0. 7) (0. 5 ) Ps where PS = the required roving vehicle probability of s u c c e s s solving, 0. 3 7 2 . This value of the roving vehicle probability of s u c c e s s i s t h e r e f o r e the c r i t e r i a against which the s y s t e m evaluation i s m a d e . Ps = 2-12 V SECTION 3 EVALUATION O F 100-LB SYSTEM 3. 1 EVALUATION SIMULATION Appendix A of EPD-98, Revision 1, r e q u i r e s that the SLRV s y s t e m be capable of verifying that the lunar landing s i t e m e e t s LEM r e q u i r e m e n t s within the following limits : 1. A 9970 confidence that 7070 of the a r e a within the s i t e i s acceptable. 2. A 90% confidence that 9570 of the area within the s i t e is acceptable. Vo ume I1 of t h i s r e p o r t shows that these r e q u i r e m e n t s can be m t with a SLRV m i s s i o n defined as the capability of verifying with 99% confidence a s e r i e s of points, e a c h 40 m e t e r s in d i a m e t e r , and distributed i n a p r e s e t p a t t e r n throughout the 3200-meter s i t e . The minimum number of acceptable points i s stated a s 13, with the d e s i r e d SLRV m i s s i o n requiring a capability of verifying 19 points. The evaluation simulation is designed to determine the probability of s u c c e s s of completing t h i s m i s s i o n as well as the p a r t i a l m i s s i o n s comp r i s i n g l e s s than 19 points. This determination is obtained a s a function of the l u n a r s u r f a c e , considering reliability, finite sampling, and p e r f e c t measurements. 3. 1. 1 Evaluation Approach The ideal approach to the evaluation might involve displays, t e r r a i n m a p s , e t c . Such a n approach, however, is time-consuming and c o s t l y and i s m o r e in keeping with operator training than initial s y s t e m evaluation. The approach taken h e r e is the u s e of a Monte C a r l o simulation w h e r e i n the s t a t i s t i c a l n a t u r e of the s y s t e m v a r i a b l e s , e . g. , t e r r a i n V 3-1 BSR 903 and reliability, m a y be p r e s e r v e d without requiring r e a l - t i m e solutions which would be likely i n the m o r e sophisticated approach. The Monte C a r l o simulation is a proven technique f o r treating a s t a t i s t i c a l problem and m a y be tailored to any degree of sophistication d e s i r e d , limited only by available knowledge of the events of the problem and the distributions describing their frequency of occurrence. The number of computer r u n s r e q u i r e d i s higher than for d e t e r m i n i s t i c p r o g r a m s , 'but is not unduly l a r g e when compared to r e a l - t i m e evaluation. Basically, the SLRV is evaluated a s to its ability to verify 19 points i n the p a t t e r n indicated i n Figure 3 - l ( a ) . In the simulation, t h i s p a t t e r n is, i n concept, laid out in a s t r a i g h t line a s in Figure 3 - l ( b ) such that direction of t r a v e l and point location a r e not accounted f o r . This simplified approach avoids consideration of the direction (left o r r i g h t ) to be taken on encountering impassable a r e a s . Such a n accounting is r e a l l y in keeping with a simulation involving t e r r a i n m a p s , which a r e not used h e r e . By ignoring the position of the points relative to the p a t t e r n center (the L E M aiming point), the fact that points close to the center a r e m o r e valuable than those on the p e r i p h e r y i s being ignored. Thus, e a c h point is weighted equally which i s somewhat s h o r t of the t r u e picture. F i g u r e 3-2 shows the relationship between PTs and the d i a m e t e r of the veritied site. PTs is defined a s the probability that the LEM, a f t e r a r r i v ing at hover altitude, is capable of t r a n s l a t i n g to a surveyed point. F r o m Figure 3-2 it is r e a d i l y seen that verification of points close to the aim point at the p a t t e r n center contribute g r e a t l y t o the L E M s u c c e s s probability. A s points f u r t h e r f r o m the center a r e verified and the verified d i a m e t e r increased, the probability i n c r e m e n t d e c r e a s e 8 . Ignoring this t r e n d by weighting a l l points equally is not a s e r i o u s simulation fault at t h i s stage, but should be incorporated i f variable s t r a t e g y is introduced. Referring once m o r e to Figure 3 - l ( b ) , it is s e e n that the e n t i r e m i s s i o n of verifying 19 points i s a repetition of the two m a j o r e v e n t s : 1. Point s u r v e y Interpoint t r a v e l . 2. Thus, the simulation i s s e t up to cover the cycle f r o m A t o B, a s shown, with 19 cycle repetitions for one m i s s i o n . During e a c h cycle, reliability data will be checked following the point s u r v e y , at t i m e s m a r k e d "R" i n 3-2 V BSR 903 19 A B (b1 F i g u r e 3.- 1 Simulation Concept V 3-3 , __.. .. . . . ... .. , . . ... . . _ ...- c, C U 0 #/ / i ICI 0 / I I / A0 I ' ."7 . k PI I ,?#. I t # /do /! .// ,C', 'T. - 26 55 .3GC: i ?Td 9 D i a m e t e r of V e r i f i e d S i t e ( m e t e r s ) Figure 3-2. Relationship Between p TS and D i a m e t e r of Verified Site 3-4 BSR 903 Figure 3 - l ( b ) . To accomplish the computation of e a c h cycle, the i n f o r m a tion flow i s As shown in F i g u r e 3-3. The simulation for one m i s s i o n consists of 19 t i m e s through the flow chart. After i n i t i a l setup, a point s u r vey is conducted and the m a r k i n g schedule consulted to d e t e r m i n e i f m a r k ing is r e q u i r e d . Operational constraints such a s DSIF availability and lunar night a r e then examined and the mission time adjusted accordingly. The operational status is then checked by testing for f a i l u r e s . If 19 points have been completed, the m i s s i o n is over and the simulation completed. Otherwise, the S L R V completes the point by travelling to the next point, corresponding to point B of F i g u r e 3 - l ( b ) . The simulation then r e t u r n s to "point survey" to s t a r t the following cycle. S e v e r a l of the routines indicated involve s t a t i s t i c a l quantities. Thus, by making a l a r g e number (100) of r u n s and tabulating the number of m i s s i o n s wherein 19 s i t e s a r e completed, the probability of m i s s i o n s u c c e s s i s then computed a s the r a t i o of the completed m i s s i o n s to the total number of t r i e s ( r u n s ) . Partial objectives, i. e . , for 18, 17, 16 points, e t c . , a r e obtained i n like manner. 3. 1. 2 Simulation Details This section p r e s e n t s in detail the content of the simulation at i t s p r e s e n t stage of development. Section 3. 1. 2. 1 p r e s e n t s a n a r r a t i v e d e s cription of the information flow; the inputs a r e d i s c u s s e d both a s to f o r m and derivation in Section 3. 1. 2. 2; finally, Section 3. 1. 2. 3 d i s c u s s e s the m a n n e r of introducing f a i l u r e s , both catastrophic and p a r t i a l . 3. 1. 2. 1 Simulation Logic \ The details of the simulation a r e shown in Figure 3-4. Major inputs a r e shown on the left, the p r o g r a m logic i n the c e n t e r , and m a j o r outputs i n the right-hand columns. The logic, a s shown in the center portion, m a y be r e l a t e d d i r e c t l y to the boxes indicated i n Figure 3-3 and a r e s o numbered. The m a j o r input variables a r e the s u r f a c e model, operational constraints, reliability, and L E M and SLRV capabilities. Any of these m a y be p e r t u r b e d to e x e r c i s e the model. Various other relations h i p s a r e r e q u i r e d for distance and time computations. These a r e d i s c u s s e d i n detail i n Section 3. 1. 2. 2. The m a j o r outputs a r e the number of points verified, and m i s s i o n time and distance. A description of the complete p r o g r a m follows, moving down from the top of Figure 3-4. V 3-5 BSR 903 L17 I, S7ART + Figure 3-3 Simulation Flow C h a r t --I- V I“i I I Rj - I I I I I --z I I I i I I I i P ~ BSR 9 0 3 I I I I I ? I -*- I I I I I I I Q) k I I I .. i - - -- _I 3-7i3-8 BSR 903 Following initial setup, which need not be d i s c u s s e d , the first point s u r v e y is conducted. This consists of determining whether the point is acceptable for L E M landing by comparing the surface model to L E M r e q u i r e m e n t s . Because the SLRV t e r r a i n capabilities a r e g r e a t e r i n e v e r y p a r t i c u l a r than the LEM landing r e q u i r e m e n t s , the question of whether the SLRV can t r a v e r s e the point need not be considered. E v e r y acceptable point can be t r a v e r s e d , and unacceptable points can be t r a v e r s e d to the extent r e q u i r e d f o r rejection. Both good and bad points are tabulated a s indicated and a suitable time and distance added for the point verification. The time and distance added a r e different for good and bad points, since a bad point need not be covered i n total on the a v e r a g e . The details of the time and distance computations a r e given i n Section 3 . 1. 2. 2 under the heading "Time, Distance Relationships -Point Survey". Since the m i s s i o n r e q u i r e m e n t s m a y include m a r k e r emplace m e n t i n the absence of suitable landmarks, a m a r k i n g subroutine h a s been included. F r o m the basic p a t t e r n being followed, a m a r k i n g schedule is developed. The subroutine simply consists of checking to s e e whether m a r k i n g is called f o r . If r e q u i r e d , a standard time i n c r e m e n t i s added to the operating time. The assumption is m a d e that no additional t r a v e l range is r e q u i r e d f o r marking, i. e . , that the m a r k e r is emplaced at a point. The next simulation event is t o include the operational r e s t r i c tions of lunar night and DSIF availability. Up to this point i n the simulation, all elapsed time h a s been entered i n the "operating" time column which o m i t s such considerations. The accumulated operating time i s now r e a d out and, by comparing with the operational schedule data, adjusted to include these considerations. This adjusted t i m e i s now t e r m e d "actual time" and is e n t e r e d a s shown. The reliability corresponding to t h i s a c t u a l t i m e is then d e t e r mined and a test for f a i l u r e s is made. Suppose f p r discussion p u r p o s e s t h a t a c a t a s t r o p h i c failure h a s occurred. In this c a s e , the surveyed point is r e m o v e d f r o m the "goodv1 tabulation, and the output data a r e s u m m a r i z e d and printed. If no f a i l u r e h a s o c c u r r e d , the SLRV p r o c e e d s to the next point. V 3-9 BSR 903 Upon r e f e r r i n g to the p a t t e r n definition, it m a y be that the patt e r n h a s been completed; i n this c a s e , the r e s u l t s a r e tabulated. Otherwise, the destination point i s r e c o r d e d a s being the next s u r v e y point and the distance to that point determined. Even with constant spacing between points, the distance to the next point m a y vary. In F i g u r e 3 - l ( a ) , f o r example, moving f r o m 1 3 to point 14 r e q u i r e s covering double the usual interpoint distance. The s u r f a c e model is then compared with SLRV capabilities to determine how much of the a r e a ahead is i m p a s s a b l e . The time and d i s tance of travel a r e then computed and added to operating time and elapsed distance. Relationships used i n this calculation a r e discussed i n Section 3. 1. 2. 2 under the heading "Time,. Distance Relationships-Interpoint Trave 1 I . After the interpoint is completed, the simulation then r e t u r n s to the point survey, with the point to be surveyed having been updated and elapsed time and distance r e c o r d e d . Thus, it is s e e n that 19 p a s s e s through the computer logic will c o r r e s p o n d to one m i s s i o n , the s u r v e y of 19 points. DSIF and Lunar Night constraints a r e i n s e r t e d e a c h cycle, and the possibility of f a i l u r e is likewise evaluated e a c h cycle. 3 . 1. 2. 2 Inputs The inputs to the simulation will be d i s c u s s e d in the o r d e r shown in F i g u r e 3 - 4 f r o m top to bottom. The f o r m of the inputs will be d i s c u s s e d and, where applicable, the a n a l y s i s o r justification for p a r t i c u l a r a p p r o a c h e s o r values will be indicated. Surface Models The selection of suitable s u r f a c e m o d e l s w a s based on the following: 1. The range of models should cover the total s p r e a d of models detailed in E P D - 9 8 Revision 1, f r o m the m o s t favorable to the m o s t a d v e r s e combination. Any single model m u s t contain s o m e t e r r a i n acceptable to LEM. Otherwise, the probability of s u c c e s s , being depende n t i n p a r t upon LEM r e q u i r e m e n t s , would be z e r o . 2. V BSR 903 3. The number of models should be limited by r e q u i r i n g that no model be justified unless it differs by a n o r d e r of m a g nitude f r o m all o t h e r s in at l e a s t one p a r t i c u l a r . Three quantities o r p a r t i c u l a r s w e r e used to d e s c r i b e a model: (1) i r r e g u l a r i t i e s (includes obstacles and c r e v i c e s ) , (2) slopes, and (3) bearing strength. These w e r e converted to the following d e s c r i p t o r s : (1) smooth vs rough, ( 2 ) flat vs steep, and (3) h a r d v s soft. The m o s t favorable model m a y then be d e s c r i b e d qualitatively a s smooth, flat, and h a r d ; m i s s i o n time over this s u r f a c e would be a minimum. The m o s t a d v e r s e model could then be d e s c r i b e d as rough, steep, and soft; maximum m i s s i o n time should r e s u l t . A quantitative definition of the above t e r m s i s a r b i t r a r y i n the absence of m e a s u r e d lunar s u r f a c e data. The e x t r e m e values (based on E P D - 9 8 ) w e r e selected as follows: 1. Max i r r e g u l a r i t i e s Max slopes - 100 cm 2. - 15O 3. Min bearing strength gradient - 1 psi/ft. The a s s u m e d distribution of various intermediate magnitudes would probably differ g r e a t l y f r o m one investigator to another. Also, it i s recognized that the a s s u m e d distributions a r e ultimately reflected i n the m i s s i o n s u c c e s s probability. Some assumption on distribution is n e c e s s a r y , however. It s e e m s likely that all magnitudes of h a z a r d s V 3-11 BSR 903 between the e x t r e m e s m a y be expected. Therefore, the distributions a s s u m e d i n the study provide for intermediate values in approximately equal amounts. Thus, the definition of I'rough" is a s shown i n F i g u r e 3-5, with maximum i r r e g u l a r i t i e s of 100 c m and significant amounts of l e s s e r magnitudes. This type of model will show the effect on m i s s i o n s u c c e s s of changes in, for example, mobility capability, since as capability grows, the percent of impassable a r e a d e c r e a s e s with a r e s u l t a n t shortening of both mission range and t i m e . The definition of "smooth" i s derived by decreasing e a c h i r r e g u l a r i t y size found in the "rough" definition by approximately a n o r d e r of magnitude. It might be noted that the selected smooth model p r e s e n t s no p r o b l e m s for e i t h e r the 100-lb SLRV o r the L E M landing. The rough s u r f a c e p r e s e n t s p r o b l e m s for both; about 4070i s i m p a s sable for the SLRV, about 20% is unacceptable to LEM. vs The definition of 71flat11 "steep" i s shown i n Figure 3-6. 0 Again, the m a x i m u m value of 15 is taken f r o m EPD-98, and lesser slopes a r e distributed i n approximately equal amounts. The f l a t model i s then derived by reducing the s t e e p one by a n o r d e r of magnitude. F o r the 100-lb SLRV, the s t e e p model p r e s e n t s no i m p a s s a b l e slopes. However, 0 since the p r e s e n t L E M r e q u i r e m e n t i s s e t a t 12 , about 10% of the slopes a r e unacceptable. Any point containing these will then be r e j e c t e d during the "point survey" subroutine. In considering bearing strength gradient, EPD-98, Revision 1, c a l l s out a minimum of 1 p s i / f t for the soft model. This i s taken a s the e x t r e m e value of Figure 3-7. I n c r e a s e d values a r e a s s u m e d to o c c u r , and the maximum value of 20 p s i / f t in the soft model is well above the acceptable limit for LEM. If the soft model had no acceptable a r e a s , all points would be r e j e c t e d during "point survey", and the probability cf s u c c e s s f o r any surface model containing the "soft" definition would lle zero. Therefore, the soft model w a s s e t up s o that 7070 is acceptablc to LEM. The "hard" definition is then d e r i v e d by i n c r e a s i n g the bearin,; strength gradient of the s o f t model by about an o r d e r of magnitude. '.?his r e s u l t s i n a model totally acceptable to L E M . The e x t r e m e models j u s t d i s c u s s e d s a t i s f y the f i r s t two r e q u i r e m e n t s outlined. The number of n e c e s s a r y i n t e r m e d i a t e m o d e l s r e q u i r e d is then easily shown to be six. By changing one p a r t i c u l a r at a time i n the m o s t favorable model (No. 1) to the a d v e r s e condition, models 2, 3, and 4 a r e generated. Thus, / Percent of Area SMeo r H Figure 3 - 5 Definition of Irregularity Models V 3- 13 BSR 903 ,. P e r c e n t of A r e a Figure 3 - 6 Definition of Slope Models BSR 903 5 P c k Q, 4J -rl d r: 20 40 60 80 /OO Percent of A r e a Figure 3 - 7 Definition of Bearing Strength Models V 3-15 BSR 903 Model De s c r iption Smooth, Flat, Hard ROUGH, Flat, Hard Smooth, S T E E P , Hard Smooth, Flat, SOFT W i l l Show Effects Of 1 2 Irregularities Slopes 3 4 Bearing Strength Models 5, 6, and 7 a r e generated by changing two p a r t i c u l a r s of model 1 for each. Thus, Model De s c r i p ti on Smooth, F l a t , Hard ROUGH, S T E E P , hard ROUGH, Flat, SOFT Smooth, S T E E P , SOFT I r r e g u l a r i t i e s and Slope s I r r e g u l a r i t i e s and Bearing Strength Slopes and Bearing Strength. W i l l Show Effects Of Model 8, the m o s t a d v e r s e , is the combination of all t h r e e a d v e r s e conditions. With these definitions and the definitions of e a c h particular as shown i n F i g u r e s 3-5, 3-6 and 3-7, the s e t of eight m o d e l s s a t i s f i e s r e q u i r e m e n t No. 3 . Table 3 - 1 s u m m a r i z e s the eight m o d e l s . These models do not i n c o r p o r a t e the concept of "effective" h a z a r d s as defined in Appendix A of EPD-98. To do t h i s r e q u i r e s relating the physical position of, for example, s o f t areas relative to i r r e g u l a r i t i e s . This is beyond the p r e s e n t simulation scope, but could be i n c o r p o r a t e d i n the future. R e f e r r i n g now to F i g u r e 3-4, it i s s e e n that the s u r f a c e m o d e l s a r e employed in both the point s u r v e y a n d the interpoint t r a v e l routines. V TABLE 3-1 SURFACE MODEL SUMMARY Model Number Irregularities Smooth ROUGH Smooth Smooth ROUGH ROUGH Smooth ROUGH Slopes Bearing Strength Hard Hard Hard SOFT Hard SOFT SOFT SOFT Flat Flat STEEP Flat STEEP Flat STEEP STEEP Note: Bold face type indicates adverse condition. T h e r e is some a r g u m e n t that the use of the s a m e model for both events is not r e a l i s t i c . F o r example, the existence of 100-cm i r r e g u l a r i t i e s in a n a r e a chosen for a point s u r v e y i s unlikely, since m a j o r obstacles could be spotted with p i c t u r e s before the s u r v e y gets underway. A location, before being considered as a possible point, would therefore contain f e w e r l a r g e obstacles. Thus, the t t r o u g h t definition should be somewhat t l e s s rugged f o r the point survey. This detail h a s not been incorporated i n the p r e s e n t simulation; the model is identical for both events. In the point survey, the percent of the s u r f a c e which is unacceptable to L E M is determined by comparing the LEM r e q u i r e m e n t s on i r r e g u l a r i t i e s , slopes, and bearing strength to those found i n the p a r t i c u l a r model i n u s e . E x p r e s s i n g this percentage as a probability that the point a r e a is good o r bad then p e r m i t s a statistical t e s t to determine i f the point in question is good. Note that for fixed L E M r e q u i r e m e n t s and a given V 3 - 17 BSR 9 0 3 surface model the probability of finding a n acceptable point is a constant. Thus, over a l a r g e number of r u n s , a fixed fraction will be s c o r e d as good with the r e m a i n d e r being bad. If a good point i s s c o r e d , the s i m u lation goes on to a standard time and distance i n c r e m e n t . However, if a bad point r e s u l t s , the question of how many t r i e s t o make a r i s e s . A t p r e s e n t , four t r i e s a r e made before the point location is abandoned. The s u r f a c e model is a l s o r e q u i r e d in the interpoint t r a v e l subroutine. By comparing SLRV mobility capabilities with the s u r f a c e model, the percent of any t r a v e l leg which is impassable i s determined. This fraction is then used i n a detour equation to compute the time and distance penalties required to avoid the impassable a r e a . Note again that f o r fixed SLRV capabilities and a given model, the p e r c e n t of i m passable s u r f a c e will be a constant. By changing the SLRV capabilities in any particular, the effect of design changes on the probability of s u c c e s s is available f r o m the simulation. It m u s t be r e m e m b e r e d , however, that r e s u l t s a r e a d i r e c t function of the s u r f a c e model used and should be viewed i n the light of t h i s limitation. LEM Landing Requirements The L E M landing r e q u i r e m e n t s input c o n s i s t s of t h r e e constants which indicate the LEM landing r e q u i r e m e n t s a s s e t f o r t h in Appendix A of EPD-98, Revision 1, combined with the m e a s u r e m e n t capabilities of the SLRV s y s t e m . Appendix A r e q u i r e s that all points containing 5 0 - c m i r r e g u l a r i t i e s be r e j e c t e d . However, i n t h i s simulation, all points containing i r r e g u l a r i t i e s g r e a t e r than 18 c m a r e r e j e c t e d to e n s u r e that all 0 effective slopes (slope plus i r r e g u l a r i t i e s ) a r e l e s s than 12 . S i m i l a r l y , 0 all t r u e slopes of 9 a r e r e j e c t e d to guarantee that no effective slopes 0 combined with i r r e g u l a r i t i e s exceed 12 , the L E M r e q u i r e m e n t . All bearing strength gradients below 12 p s i / f t a r e a l s o cause for rejection. The LEM capability is t h e r e f o r e a s t r o n g factor i n determining SLRV s u c c e s s i n that lower L E M landing capability m e a n s m o r e s e a r c h ing by SLRV. Another significant consideration i s the i n c r e a s e i n L E M landing probability afforded by SLRV o v e r a blind landing by LEM. F o r a "good" moon, the SLRV would contribute m u c h l e s s than f o r a rfbad" moon. This consideration i s beyond the scope of the evaluation. 3- 18 V Time, Distance Relationships-Point Survey To complete the point survey subroutine a f t e r determining whether a good o r bad point h a s been s c o r e d , the time and distance r e q u i r e d f o r the s u r v e y is computed and e n t e r e d a s operating time. This computation differs somewhat depending upon whether a good point is found on the first t r y o r whether s e v e r a l t r i e s (searching) a r e required. F o r a complete point survey, the computations for time and distance i n c r e m e n t s , respectively, a r e AT = T D ( l t Lm a x K 8) (3- 1) AD = D D ( l t L where TD = time to s u r v e y a good point K ) max 8 DD = distance a c c r u e d i n surveying a good point L Max = number of false s t a r t s before finding the good point K8 = Average fraction of total s u r v e y completed before point is rejected. Equation (3-1) t h e r e f o r e consists of adding a nominal t i m e and distance for the good point plus a n allowance for any false starts r e q u i r e d before the good one w a s found. The time T includes the following i t e m s : D Time (minutes) 1. Decision making TV t r a n s m i s s i o n TV slew 558 118 124 2. 3. V 3 - 19 BSR 903 Time (minutes) 4. 5. Antenna slew Travel P e n e t r o m e t e r ope ration Total 10 173 6. 96 1079 The distance DD i s a function of the p a t t e r n used in the s u r v e y and is the total of a l l distances shown i n Figure 3 - l ( a ) . The number of f a l s e starts to be allowed i s determined f r o m s t r a t e g y analysis and i s p r e s e n t l y s e t at four. The constant K8 is e s t i m a t e d to be 0. 4 based on examination of the following reasons for abandoning s u r v e y s : 1. I r r e g u l a r i t i e s too l a r g e for L E M Slopes too s t e e p f o r a L E M landing Soil too soft for a L E M landing. 2. 3. There i s a n equal probability of rejection for the f i r s t two r e a s o n s anywhere within the point; hence, a bad point would be r e j e c t e d at the halfway m a r k (on the a v e r a g e ) . A f a i r l y good indication of the s o i l c h a r a c t e r i s t i c s ( r e a s o n 3 ) will be obtained before the f i r s t half of the point s u r v e y is completed, as it is quite unlikely that t h e r e will be a b r u p t changes in the s o i l bearing strength. Thus, finding the first half acceptable will provide high confidence that the e n t i r e point i s acceptable. On the a v e r a g e , point rejection f o r inadequate bearing s t r e n g t h i s expected to occur when 2570 of the point s u r v e y is completed. Taking the a v e r a g e of the completed portion for the t h r e e c a s e s r e s u l t s in a value of K = 8 0. 5 t 0. 5 t 0. 25 3 = 0.4. T h e r e f o r e , a factor of 4070i s used as the a v e r a g e completed portion f o r e a c h rejected point. V BSR 903 Marking Schedule The marking schedule f o r the fixed s t r a t e g y input c o n s i s t s only of a r e c o r d of the points where marking i s to be accomplished. A typical schedule c a l l s f o r m a r k i n g at points 4, 7, and 10. When m a r k i n g is r e quired, a nominal six minutes is added to operating t i m e . N o distance i n c r e m e n t is entered, since the marking o c c u r s at the s u r v e y points. Reliability Data The reliability input p r e s e n t l y used is the reliability vs time curve shown a s Figure 3-8. The details behind this curve a r e given in Volume IV and a r e not repeated h e r e . The use of this curve in determining whether a failure h a s o c c u r r e d shouldbe explained. F i g u r e 3-8 indicates only the probability of a failure as a function of a c t u a l time. If reliability i s initially checked at point ( l ) , corresponding to completion of point # 1 and time adjustment # 1, the probabilityof reliability is R1. Thus, t o t e s t w h e t h e r a f a i l u r e h a s actually o c c u r r e d i n the mission at t h i s point, the probability of s u c c e s s f u l operation is R1. If point ( 2 ) then c o r r e s p o n d s to completion not of point s u r v e y #2, t i m e adjustment # 2 , the reliability t e s t i s -m a d e with a probability of s u c c e s s (no faiIure) af R 2 , but ratlier is an event'with probability of s u c c e s s R2/R1. A s the time t 2 moves towards t l , the r a t i o R2/R1 approaches unity. Operational Constraints F i g u r e 3-9 shows the following constraints on operating t i m e : 1. A 24-hour period immediately a f t e r dawn i n which s y s t e m w a r m up is completed and i n which operation is i m p r a c t i c a l because of poor visibility 2. P e r i o d s when the DSIF i s unavailable A s h o r t p e r i o d centered about high noon when sun s e n s o r limitations a r e p r e s e n t A 24-hour period immediately preceding nightfal when visibility m a k e s operation impractical 3. 4. 5. Lunar night. V 3-21 BSR 903 3-22 V . . d .i ; c, cd k 0 V 3-23 BSR 903 These constraints a r e i n s e r t e d to convert "operating t i m e " to "actual time'' which i n c r e a s e s the m i s s i o n t i m e to include these standby periods. Roving Pattern Definition Definition of the roving p a t t e r n w a s the r e s u l t of m i s s i o n and s y s t e m studies and w a s shown in F i g u r e 3 - l ( a ) . A s a n input to the p r e s e n t s i m u lation, the p a t t e r n is a listing of the point sequence to be followed together with the interpoint distance. SLRV T e r r a i n Capabilities The SLRV t e r r a i n t r a v e r s i n g capabilities r e q u i r e d a r e t h r e e with c u r r e n t value s a s shown: 1. 2. 3. Maximum i r r e g u l a r i t y Maximum slope - 30 c m - 15 0 Minimum bearing s t r e n g t h gradient - 1. 0 p s i / f t . During the interpoint t r a v e l subroutine, these capabilities a r e c o m p a r e d with the surface models to d e t e r m i n e the percentage of the distance to the next point which is impassable. Time, Distance Relationships -Interpoint Travel The final s t e p in the interpoint t r a v e l routine is the computation of the time and distance r e q u i r e d to t r a v e l to the destination point. In the ideal c a s e , with no h a z a r d o r i m p a s s a b l e t e r r a i n , the distance t r a v e l l e d would be just the straight-line interpoint distance, and the time r e q u i r e d j u s t the straight-line distance divided by the a v e r a g e r a t e of t r a v e l . The r a t e of travel includes such effects a s : (1) time f o r a c t u a l t r a v e l , ( 2 ) data collection, ( 3 ) t r a n s m i s s i o n , and (4) decisions. T h e s e i t e m s include everything in the point s u r v e y time calculations except the p e n e t r o m e t e r . When impassable a r e a s a r e encountered, the SLRV m u s t d e t o u r . The amount of this detour depends upon the s e v e r i t y of the m o d e l and is d i s c u s s e d l a t e r . The computation of the interpoint t r a v e l distance and time a r e made a s follows V BSR 903 A D = D. (1 t 6 F) 1 F AT = AD V (3-2) where D. = straight-line distance of the i t h l e g of the p a t t e r n 1 6 F = detour distance deviate ( 0 - 6 < 2) < F= detour distance factor = average interpoint r a t e of travel. F V avg The factor F is the m e a n additional fraction of the straight-line distance which is r e q u i r e d f o r detouring around impassable a r e a s . The deviate, 6F, provides for the distribution about this mean. F i g u r e 3- 10 shows the magnitude of detour factor F a s a function of the percentage of a t r a v e l distance which is i m p a s s a b l e . The dotted line indicates values obtained by a graphical a n a l y s i s (experimental), while the solid line is the equation F = where 0. 559A (1-~)1.4 (3-3) A = fraction of a r e a which i s impassable. This function, being quite close to the experimental c u r v e , i s used in the simulation. Thus Equations (3-2) and (3-3) a r e employed to compute the interpoint time and distance. These computations complete the simulation cycle. The method of generating the experimental curve for detour factor F will now be discussed. T h r e e basic r e q u i r e m e n t s w e r e established which m u s t be m e t by the approach: V 3-25 BSR 903 I! ! j I I _ F i g u r e 3-10 Detour F a c t o r , F 3-26 i . - BSR 903 1. The statistical nature of the detour situation should be p r e s e r v e d . Thus any simple, constant penalty i s outlawed. Any relationship derived should be t r a c e a b l e to a definite s u r face model. The surface model definition should p e r m i t s e p a r a t e investigat o r s to generate the same F-curve independently. 2. 3. The s t a r t i n g point i n the approach is the percent of the s u r f a c e which is i m p a s s a b l e . In the simulation, t h i s r e p r e s e n t s i r r e g u l a r i t i e s with d i m ensions exceeding the L R V capability. Since it w a s a s s u m e d that the size and makeup (e. g. , whether in chains o r not) of obstacles was dominant in determining the detour magnitude, random m a p s w e r e generated on the b a s i s of: 1. Obstacle s i z e - h e r e a f t e r t e r m e d "kernel" s i z e , since it m a y r e p r e s e n t other than obstacles P e r c e n t of t o t a l m a p area which is i m p a s s a b l e ; i. e . , the p o r tion which' contains kernels. 2. The m a p is generated by using a square grid with e a c h s q u a r e r e p r e s e n t i n g one k e r n e l . F r o m a random number selection based on the percentage bad (and t h e r e f o r e the probability that any s q u a r e is a k e r n e l ) , the complete g r i d is covered one s q u a r e a t a time, determining whether e a c h s q u a r e is a k e r n e l o r not. A simple check on the r e s u l t s is made by counting the s q u a r e s s c o r e d a s kernels and computing the actual percentage of the m a p which is impassable. Illustrative m a p s a r e shown in Figure 3 - 11 and 3 - 12 for 2070 bad and Note that the formation of chains (akin to c r e v i c e s , r i d g e s , e t c . ) is automatic. F u r t h e r m o r e , as the percentage bad i n c r e a s e s , detour direction becomes m o r e difficult to choose, and blind alleys a l s o o c c u r . F r o m the b a s i c information of kernel s i z e and percentage bad, one c a n g e n e r a t e any number of m a p s . A l l of these are different, but all will have the s a m e s t a t i s t i c a l p r o p e r t i e s and a r e t h e r e f o r e "identical" a s far a s detour computations a r e concerned. 5070 bad, respectively. V 3 -27 BSR 9 0 3 Figure 3 - 1 1 Random T e r r a i n Map, 2070 Bad 3-28 V . . BSR 9 0 3 Figure 3-12 Random T e r r a i n Map,' 5070 Bad V 3 -29 I BSR 903 After deriving s e v e r a l m a p s of various percentages bad, one point on the F - c u r v e can be determined f o r e a c h map. This was done by placing an overlay of the 19-point roving p a t t e r n on each m a p and t r a c i n g feasible interpoint t r a v e l routes for the mission, detouring around k e r n e l s a s r e q u i r ed. The amount of detour was tabulated and t h e m e a n computed f o r each map. The deviate A r e p r e s e n t s the distribution about t h i s mean. F A s a p a r t of t h i s study, the effect of k e r n e l s i z e on detour distances was a l s o investigated. The s a m e m a p s w e r e used, but the p a t t e r n o v e r l a y was varied in s i z e , giving the effect of a different k e r n e l size. The "20% bad" m a p was checked with the following r e s u l t s : Map Definition 70 bad 20 20 Kernel Size 17. 5 m e t e r s Value f o r F 0. 15 0.20 88 176 20 0. 14. Little differences w e r e found in the F value as k e r n e l s i z e v a r i e d . However, m o r e work m u s t be done to substantiate t h i s conclusion. Kernel shape was a l s o considered, the s q u a r e and c i r c l e receiving m o s t attention. The c i r c l e is s u p e r i o r to the s q u a r e in one r e s p e c t ; the detour around a c i r c l e i s independent of the direction of approach f o r a given offset f r o m the c e n t e r . This is not t r u e for the s q u a r e . To compensate somewhat i n t h i s work f o r t h i s fault of the s q u a r e , a n equal number of c a s e s w e r e taken for both directions I & I1 shown in F i g u r e 3-12. Generating m a p s using c i r c u l a r k e r n e l s was generally m o r e t i m e consuming and evaluation m o r e difficult than when using s q u a r e s . The s q u a r e s , m o r e o v e r , can quite e a s i l y be m a d e t o r e p r e s e n t any shape of h a z a r d simply by making the kernel s i z e small enough. Also, when c i r c l e s a r e used, t h e r e i s quite a bit of a r e a which m u s t be accounted f o r between adjacent c i r c l e s . Referring back to the t h r e e r e q u i r e m e n t s i n the opening p a r a g r a p h , it is s e e n that r e q u i r e m e n t No. 1 is s a t i s f i e d since the detour distance is V BSR 903 r e p r e s e n t e d by a m e a n F depending on the percentage of the a r e a which is bad. The distribution about the m e a n is r e p r e s e n t e d by t h e random deviate Also, any F - c u r v e such as F i g u r e 3-10 is d i r e c t l y r e l a t e d t o a definite s u r f a c e model defined by (a) percentage bad and (b) k e r n e l s i z e . Thus the second r e q u i r e m e n t is m e t . Finally, if a n investigator starts with a given percentage and k e r n e l s i z e , he c a n u s e a random number table to g e n e r a t e a m a p , differing in detail f r o m that of another investigator working independently, but identical in s t a t i s t i c a l p r o p e r t i e s ; t h e r e f o r e it will r e s u l t i n the s a m e F - c u r v e . Thus the t h i r d r e q u i r e m e n t is m e t . s. It should be noted that the F - c u r v e shown in F i g u r e 3-10 r e p r e s e n t s a minimum value, because the ready-made m a p was p a r t i a l l y visible to the "SLRV operator". The detour distances would be longer when o p e r a ting m o r e blindly, e. g . , like a m o u s e in a m a z e . 3 . 1.2. 3 Failures The t r e a t m e n t of vehicle f a i l u r e s in the simulation d i f f e r s , d e pending on whether the f a i l u r e s under investigation a r e c a t a s t r o p h i c o r partial. Catastrophic Failures When a f a i l u r e is catastrophic, the approach is e s s e n t i a l l y the one outlined in Section 3. 1. 3. 1. A single reliability v s t i m e c u r v e is u s e d as t h e b a s i s for reliability testing following e a c h point s u r v e y and t i m e a d j u s t m e n t . If a f a i l u r e h a s not o c c u r r e d , the simulation m e r e l y p r o c e e d s . If a f a i l u r e has o c c u r r e d , the m i s s i o n is t e r m i n a t e d , and the r e s u l t s a r e tabulated. Partial F a i l u r e s Two approaches a r e c u r r e n t l y being used t o evaluate the effects of p a r t i a l f a i l u r e s . In t h e f i r s t approach, a p a r t i a l f a i l u r e is i n s e r t e d at the beginning of the m i s s i o n . The b a s i c s y s t e m reliability c u r v e f o r c a t a s t r o phic f a i l u r e is a l s o i n s e r t e d . The d e c r e a s e in probability of s u c c e s s due to the p a r t i a l f a i l u r e is then evaluated. By studying m a n y p a r t i a l f a i l u r e s in t h i s m a n n e r , the c r i t i c a l i t y of individual f a i l u r e s m a y be d e t e r m i n e d . To i n s e r t t h e p a r t i a l f a i l u r e , the input data a r e changed, i. e . , LRV capabilities i n t e r r a i n negotiation, a v e r a g e speed, e t c . , a r e degraded. The m a j o r V 3-31 BSR 903 problem in evaluating p a r t i a l f a i l u r e s is of c o u r s e to determine the amount of degration brought about by a p a r t i c u l a r failure. In the second approach, the s y s t e m reliability c u r v e is broken down into a number of c u r v e s , each representing the reliability of a subs y s t e m o r component of i n t e r e s t . T h e r e is a b a s i c c u r v e r e p r e s e n t i n g those items not broken out individually, this c u r v e shows a higher reliability than the previous total s y s t e m reliability curve. Each c u r v e is t e s t e d during the reliability subroutine to determine if f a i l u r e s of the applicable i t e m s have o c c u r r e d . When a failure o c c u r s , appropriate changes a r e m a d e in vehicle performance constants, and the mission is continued. Because of analysis limitations, the o c c u r r e n c e of two p a r t i a l f a i l u r e s during a mission i s t r e a t e d as a catastrophic failure a t the t i m e of the second failure, and the m i s s i o n is t e r m i n a t e d . 3. 1 . 2 . 4 Adaptive Mission The adaptive m i s s i o n is a variation of the b a s i c m i s s i o n in which the method of determining the interpoint t r a v e l and point s u r v e y t i m e and distance i s changed. This m i s s i o n is intended t o show the effects of a n adaptive type of s t r a t e g y in which learning plays a r o l e . The 19 points a r e surveyed in the s a m e o r d e r a s f o r the b a s i c mission, but the r a t e at which m i s s i o n t a s k s a r e accomplished is m a d e a function of how good o r bad the l u n a r surface i s found to be. The point s u r v e y t i m e and distance a r e longer where the surface is marginally acceptable, and s h o r t e r where the s u r f a c e i s either obviously acceptable o r not acceptable. E a c h point to be surveyed i s placed in one of four c a t e g o r i e s , depending on the s u r f a c e model: 1. 2. Obviously good Marginally good Marginally bad Obviously bad. 3. 4. The t i m e and distance i n c u r r e d in surveying the point a r e then determined according to the category into which the point f a l l s . The i n t e r point t r a v e l time is gradually d e c r e a s e d a s m o r e and m o r e good a r e a is found. When difficult t e r r a i n i s encountered, the interpoint t r a v e l is again increased. 3-32 V . BSR 903 3.2 SIMULATION RESULTS The r e s u l t s of the evaluation of the 100-lb SLRV will be d i s c u s s e d in the following o r d e r : 1. Probability of mission success a s a function of the lunar s u r f a c e conditions Mission duration and distance a s a function of the l u n a r s u r f a c e conditions. Probability of m i s s i o n success as a function of SLRV reliability, considering both catastrophic and p a r t i a l f a i l u r e s Probability of m i s s i o n success when SLRV t a c t i c s a r e made a function of the l u n a r s u r f a c e conditions (adaptive m i s s i o n ) . Probability of Mission Success 2. 3. 4. 3.2.1 The probability that the SLRV can successfully complete the m i s s i o n of 19 points was found to be 0.30, using the b a s i c (nonadaptive) m i s s i o n and a combination of s u r f a c e models. The probability of meeting p a r t i a l m i s s i o n objectives ( l e s s than 19 points) i s shown in F i g u r e 3-13. The i m p a c t of the lunar s u r f a c e on the probability of s u c c e s s is s e e n f r o m the t h r e e c u r v e s . Surface model No. 1 was used f o r the highest c u r v e , and s u r f a c e model No. 8 f o r the lowest curve; t h e s e s u r f a c e models yielded the highest and lowest probability of success, respectively. This was to be expected since models 1 and 8 r e p r e s e n t the m o s t favorable and m o s t a d v e r s e m o d e l s , respectively. The middle curve shows the r e s u l t s f r o m u s e of a composite of the s u r f a c e models, where each s u r f a c e model was u s e d a n equal number of t i m e s . It is s e e n f r o m F i g u r e 3-13 that both the No. 8 and composite s u r f a c e model c u r v e s "drop off" n e a r the end of the mission, while the N o . 1 s u r f a c e model c u r v e does not. The r e a s o n is that the mission was always ended a f t e r the 19th s u r v e y point, r e g a r d l e s s of whether o r not 19 good points had a l r e a d y been found. Only the good points w e r e used in calculating the probability of s u c c e s s . Several bad points w e r e found on m o s t of the m i s s i o n s on s u r f a c e model No. 8 which is the rough, steep, soft s u r f a c e . However, v e r y f e w bad points w e r e found on the No. 1 s u r f a c e model which i s a smooth, flat, h a r d surface. V 3-33 . BSR 9 0 3 I 3-34 BSR 903 The No. 1 s u r f a c e model probability c u r v e is not a smooth c u r v e because of the d e c r e a s e in reliability during the long l u n a r night. The No. 1 s u r f a c e model i s relatively e a s y t o survey, so each m i s s i o n t a k e s about the s a m e time. Lunar night falls a f t e r the s u r v e y of points 2, 7, 12, and 16 which accounts for the d r o p in the probability c u r v e a t t h e s e points. This effect is not as apparent on the other s u r f a c e models, because the m i s s i o n durations v a r y m o r e and lunar nights do not o c c u r a f t e r a definite point s u r v e y but a r e somewhat scattered. The probability of s u c c e s s f o r completing the s u r v e y of a given number of points was found by calculating the percentage of the t o t a l number of m i s s i o n s in which at l e a s t the given number of good points was surveyed. It should be kept i n mind that the probability of s u c c e s s a s defined h e r e includes neither the probability of successful deployment nor the possibility of human e r r o r in control of the mission. The probability of s u c c e s s on s u r f a c e models 2 , 3 , and 4 a r e shown in F i g u r e 3-14. Each of these surface models is a d v e r s e in one of the t h r e e p a r t i c u l a r s used to d e s c r i b e the s u r f a c e . The s u r f a c e model No. 1 c u r v e is included again f o r comparison. T h e r e is l i t t l e difference between the No. 1 and No. 3 s u r f a c e model c u r v e s . Slopes a r e s t e e p e r on s u r f a c e model No. 3 , but all the slopes a r e still t r a v e r s a b l e by SLRV and m o s t of t h e m a r e acceptable f o r LEM landing. The difference between the No. 1 and No. 2 s u r f a c e model curves is much g r e a t e r . Surface model 2 contains a considerable amount of a r e a which is not acceptable for both SLRV t r a v e r s e and LEM landing. Results f o r s u r f a c e models 5, 6, and 7 a r e shown i n F i g u r e 3-15. T h e s e s u r f a c e models a r e a d v e r s e in two of the t h r e e p a r t i c u l a r s . Again, s u r f a c e model No. 1 is included f o r comparison. Surface model No. 7 is not v e r y much m o r e difficult than surface model No. 1, even though both s l o p e s and bearing strength a r e in the a d v e r s e category. This is s i m p l y b e c a u s e the SLRV can still t r a v e r s e all of the a r e a in the s u r f a c e model. S u r f a c e models 5 and 6 , however, a r e m o r e difficult because i r r e g u l a r i t i e s a r e included in both models. 3 . 2. 2 Mission Duration and Distance The a v e r a g e mission duration and total distance t r a v e l e d a s a function of the s u r f a c e model a r e shown in F i g u r e 3 - 16. Mission durations V 3-35 . . BSR 903 i -iI 1 . . . I . I i 1 , - - . . I - ... -__._ . I . . . . . . I . . ' ' ' g ! x i I 3-36 V BSR 903 i i . . . .I . . 1 +--.+ ---- i 1 ,:I e __ - .. ! I i L I I. I ... * I i ' 1 ! I - - - f i i > rYn a d z $--%-%E E: E I d ! + . '! i i . V 3-37 BSR 9 0 3 I 4 / w Y I I ? s I I 4 , I Mission Dudation ( M o ~ s ) I Figure 3-16 Effect of Surface Model on Mission Duration and Distance 3-38 V BSR 903 and distances w e r e a v e r a g e d f r o m those m i s s i o n s in which 19 good point s u r v e y s had been completed. It i s seen that t h e r e is a s t r o n g relationship between m i s s i o n duration and distance, which is to be expected. Mission duration v a r i e s f r o m 3. 67 months on surface model No. 1 t o 5. 35 months on s u r f a c e model No. 8, with a m e a n of 4. 56 months. Total distance t r a v e l ed during the m i s s i o n v a r i e s f r o m 20.6 km on s u r f a c e model No. 1 to 29. 6 km on s u r f a c e model No. 8, with a m e a n of 2 5 . 4 km. T i m e s and distances a r e longest on models 2 , 5, 6, and 8, all of which contain the m o r e s e v e r e i r r e g ularities. 3. 2. 3 Reliability Effects f The probability of m i s s i o n success was d e t e r m i n e d with two diff e r e n t reliability l e v e l s . The r e s u l t s a r e shown in F i g u r e 3-17. Each s u r f a c e model was u s e d a n equal number of t i m e s to m a k e the r e s u l t s independent of t h e s u r f a c e model. The lower c u r v e r e p r e s e n t s the predicted SLRV reliability for the p r e s e n t design ( s e e Volume IV). The upper c u r v e is t h e s a m e as that shown in F i g u r e 3-13 and was plotted using the r e l i a bility data shown in F i g u r e 3-8. These data a r e b a s e d on the anticipated r e l i a b i l i t y growth as the p r o g r a m p r o g r e s s e s . A l l of t h e above r e s u l t s w e r e obtained under the assumption that all f a i l u r e s a r e catastrophic. This i s obviously a r a t h e r conservative a s s u m p t i o n , because many f a i l u r e s will m e r e l y c a u s e a slowdown of the m i s s i o n . Since determining the effect of e a c h of the m a n y possible p a r t i a l f a i l u r e s i s v e r y complex, only s i x partial f a i l u r e s have s o f a r been cons i d e r e d . The details of the a p p r o a c h in handling p a r t i a l f a i l u r e a r e contained in p a r a g r a p h 2 under the heading " P a r t i a l F a i l u r e " in Section 3. 1. 2. 3. The probability of m i s s i o n success with s e l e c t e d p a r t i a l f a i l u r e s i n c o r p o r a t e d in the simulation is shown in F i g u r e 3-18. The c u r v e ( F i g u r e 3-13) in which all f a i l u r e s w e r e considered c a t a s t r o p h i c is shown again f o r c o m p a r i s o n . It is s e e n that f u r t h e r operation a f t e r a p a r t i a l f a i l u r e gives a slight i n c r e a s e in t h e probability of m i s s i o n s u c c e s s . The r e s u l t s shown w e r e obtained using the composite surface model to m a k e them independent of the s u r f a c e model. The p a r t i a l failures which w e r e considered a r e a s follows : 1. R F ranging 1 V 3-39 BSR 903 m m I I I ! iI 7-- 7 I I V .SR 9 0 3 - .I I ) r( Q I I ; I 9 d .r( cn 0) -. w 0 , 0 c 4 Id .r( I id k d rcl 0 u . . _ w w 0) W _* . .* . i . . , . , .. - .. . . . . r - ' i ~ .. . - i V 3-41 BSR 903 2. 3. 4. T r a c t i o n d r i v e m o t o r (one t r a c k ) Directional antenna TV azimuth pan TV r e s t r i c t e d to l o o field of view TV, 50% l o s s of resolution. 5. 6. To d e t e r m i n e the effects of each of the above p a r t i a l f a i l u r e s , the p a r t i a l f a i l u r e s w e r e i n s e r t e d s e p a r a t e l y a t the beginning of the m i s s i o n a s described under " P a r t i a l F a i l u r e s " in Section 3 . 1. 2. 3. The r e s u l t s a r e shown in F i g u r e s 3-19, 3-20, and 3-21. Each figure includes f o r c o m p a r i son the probability of s u c c e s s without the f a i l u r e . Again, the composite s u r f a c e model was used f o r all c u r v e s . A maximum of 10 point s u r v e y s w e r e attempted in these m i s s i o n s before a point was abandoned (compared t o only four t r i e s in the basic m i s s i o n ) . Thus, the number of bad points found was negligible, and the c u r v e s r e f l e c t only the reliability of the SLRV and a r e not influenced because of f a i l u r e t o find a good point on the 19-point s u r v e y attempts. The m o s t c r i t i c a l p a r t i a l f a i l u r e of the s i x considered w a s failure of the R F ranging subsystem. T h e probability of completing the mission was 0. 11 a f t e r the R F ranging f a i l u r e . T h i s c o m p a r e s to a probability of s u c c e s s of 0 . 4 2 with no p a r t i a l failure. 3. 2.4 Adaptive Mission The probability of s u c c e s s for the adaptive m i s s i o n is shown in F i g u r e 3 - 2 2 . These c u r v e s follow the s a m e t r e n d a s those for the b a s i c mission which w e r e given in F i g u r e 3-13. The s p r e a d between the c u r v e s f o r surface models 1 and 8 is a l s o approximately the s a m e . B e c a u s e of the s h o r t e r m i s s i o n t i m e s using the adaptive approach, only two l u n a r nights o c c u r r e d during the total m i s s i o n . The basic m i s s i o n usually extended over t h r e e lunar nights. L u n a r night, as explained f o r the b a s i c mission, accounts f o r the sudden d r o p s i n the c u r v e of No. 1 at points 4 and 14. A comparison between the two approaches is shown in F i g u r e 3-23, using the d a t a of F i g u r e 3-13 and 3-22 f o r the composite s u r f a c e model. The probability of successfully verifying 19 points i n c r e a s e d f r o m 0. 30 to BSR 903 V 3 -43 BSR 903 V BSR 903 ;I - -- P e-. . . . .. ! - . . - . I . - J I I - ! I 0) & d a .r( a u .r( c.c k ld I ! d V 3-45 BSR 903 i I . .. . i I I I i I I iI I I I ! I I .. I I I j I 1 i I 1 1 j I I I I 1 I 1 I I 1 i I I I I 1 I ! I i i I i I I I i ! ! I I I I 3 -46 V BSR 903 3- - ~ ? I I I I ! . -. . ..- . -. h I I! * - I .. .. I I I i I ! - ' - ~ . -. I .. -- I ,! . . . - . . .- - - ! i i I 1 I I ! I ,I I j I I i i I . I i I 1 I----.. % I j . . V 3-47 BSR 903 0 . 3 9 f o r a gain of 0 . 0 9 o r approximately one-third. Verification of 13 points, defined as the minimum mission, shows a gain f r o m 0. 62 to 0. 72 (1470,)i n the probability of s u c c e s s . Thus, the relative gain is g r e a t e r as the mission i s extended. The gain in m i s s i o n s u c c e s s probability achieved by the adaptive m i s s i o n is of c o u r s e d i r e c t l y related to the s h o r t e r m i s s i o n t i m e s and attendant reliability gains. The magnitude of the saving in m i s s i o n t i m e i s shown in F i g u r e 3-24 f o r a l l s u r f a c e models. The t i m e s f o r the basic m i s s i o n a r e identical to those shown in F i g u r e 3-16. The a v e r a g e m i s s i o n t i m e dropped approximately 1- 1/ 2 months, resulting i n a value of slightly o v e r t h r e e months. This r e p r e s e n t s a reduction of about 3570. The mission distance under the adaptive approach is roughly the s a m e a s f o r the b a s i c m i s s i o n which w a s shown in F i g u r e 3-16 and t h e r e f o r e i s not shown. 3.3 ROVING PATTERN STRATEGY The s t r a t e g y f o r choosing between v a r i o u s roving p a t t e r n s (overall s i t e verification p a t t e r n s ) cannot be detailed without f i r s t looking a t the strategy which might be employed throughout the SLRV p r o g r a m . Thus, the approach i n t h i s section will be to f i r s t d i s c u s s o v e r a l l p r o g r a m s t r a t e g y , followed by the s t r a t e g y r e q u i r e d f o r an individual m i s s i o n . Finally, an example will be given of the application and r e s u l t s of the b a s i c r u l e s of strategy for the 19-point verification m i s s i o n . 3.3. 1 P r o g r a m Strategy A simplified representation of the problem of p r o g r a m s t r a t e g y is shown in F i g u r e 3-25. On the f a r l e f t , a few of the elements entering p r o g r a m strategy a r e shown. Thus, given the SLRV p r o g r a m r e q u i r e m e n t s , the problem is one of determining how b e s t t o fulfill t h e s e with a given number of flights. The main point t o be m a d e h e r e is that s t r a t e g y f o r individual SLRV m i s s i o n s should not n e c e s s a r i l y be identical f o r a l l f l i g h t s . The strategy i s defined by the o v e r - a l l p r o g r a m goals, the number of flights in the p r o g r a m , c u r r e n t knowledge of the l u n a r s u r f a c e , and a multitude of other considerations. Data f r o m all s o u r c e s , which include t e r r e s t i a l observations, Ranger, and e a r l y Surveyor f l i g h t s , e t c . , should s e r v e a s bases f o r the l u n a r s u r f a c e model and, t h e r e f o r e , m i s s i o n s t r a t e g y . 3 -48 V BSR 903 Figure 3-24 Effect of Surface Model on Mission Duration for Adaptive Mission V 3-49 BSR 903 I I I I I I I I I I 1 I I I I I I I I I I '1 I I I I I I I I I I I I I I I I I I I I I I I I 3-50 BSR 903 The p r e d i c t e d SLRV r e l i a b i l i t y will also be a f a c t o r in individual m i s s i o n definition. It s e e m s reasonable that e a r l y m i s s i o n s would be s h o r t e r and s i m p l e r in o r d e r to achieve a high probability of s u c c e s s . With reliability growth in the middle and l a t e p r o g r a m s t a g e s , the m i s s i o n s will i n c r e a s e in complexity and duration in keeping with the improved reliability. A s F i g u r e 3 - 2 5 indicates, the output of the p r o g r a m s t r a t e g y is a definition of the m i s s i o n f o r e a c h flight. A s d a t a a r e r e c e i v e d f r o m other p r o g r a m s and f r o m e a r l y SLRV flights, the p r o g r a m s t r a t e g y m a y be modified. Likewise, as the number of SLRV flights is i n c r e a s e d o r dec r e a s e d , the individual flight m i s s i o n s must be modified. 3. 3. 2 Mission Strategy Mission s t r a t e g y is defined as the plan for operating the vehicle on the l u n a r s u r f a c e . This plan m u s t include, not only the m e a n s of choosing the b a s i c p a t t e r n to be covered, but a l s o the c r i t e r i a f o r modifying the p a t t e r n on the b a s i s of data returned. The b a s i c question which d e t e r m i n e s the p a t t e r n to be followed is the knowledge of the l u n a r s u r f a c e at flight t i m e . Two fundamentally d i f f e r e n t approaches m a y be taken i n any flight: 1. 2. A r e a sampling Point verification. In a r e a sampling, the SLRV t r a v e l s o v e r the s u r f a c e according t o a p a t t e r n designed on a s t a t i s t i c a l b a s i s . E v e r y m e a s u r e m e n t taken by the SLRV is t r e a t e d a s a s a m p l e , and the n a t u r e of the s u r f a c e is p r e dicted on the b a s i s of the number of samples taken, the acceptability of e a c h m e a s u r e m e n t , spacing between m e a s u r e m e n t s , etc. On the b a s i s of the e a r l y m e a s u r e m e n t s , the pattern is modified t o c o v e r succeeding a r e a s i n l e s s e r detail, relying on s t a t i s t i c s to provide the d e g r e e of confidence in the total s i t e acceptability. In point verification, the total a r e a is not c o v e r e d . A number of points of sufficient s i z e f o r a LEM landing a r e 100% verified and located throughout the landing s i t e i n a pattern permitting the LEM to r e a c h at l e a s t one f r o m any hover point above the landing s i t e . V 3-51 BSR 903 There a r e two fundamental differences between the two approaches: 1. The d e g r e e of lunar s u r f a c e homogeneity which m u s t be a s s u m e d in using each approach. The applicability of each approach to a d v e r s e s u r f a c e conditions. 2. In the a r e a sampling approach, considerable homogeneity is a s s u m ed. That i s , in o r d e r to obtain the r e q u i r e d confidence in the e n t i r e a r e a on the basis of a reasonable number of m e a s u r e m e n t s , one m u s t a s s u m e that the samples within the 3200-meter s i t e c o m e f r o m a given distribution and that a s m a l l sample a r e a will yield the s a m e distribution. However, it is e a s y to s e e that i f , f o r example, l a r g e soft a r e a s abound in low sample a r e a s , the conclusions drawn on the b a s i s of highly-sampled good a r e a s will be erroneous. This i s i l l u s t r a t e d pictorially in F i g u r e 3-26 w h e r e in e f f e c t a s p i r a l p a t t e r n is a s s u m e d , with sampling d e c r e a s i n g a s a function of distance f r o m the c e n t e r . To avoid t h i s difficulty, either the sampling r a t e m u s t be retained a t a f a i r l y high level, meaning many m e a s u r e m e n t s with long mission t i m e s , o r a n assumption of homogeneity in a r e a s much s m a l l e r than the s i t e s i z e m u s t be made. With the point verification approach, no assumption of homogeneity need be made, since the points a r e 100% verified and the intervening a r e a s a r e of small importance to LEM. The need f o r a l a r g e number of m e a s u r e m e n t s i s also avoided because of the e x t r e m e l y small percentage of t o t a l a r e a verified. The applicability of each approach to a d v e r s e t e r r a i n i s a l s o v e r y important. With a given vehicle, r e g a r d l e s s of i t s mobility capabilities, the approach should allow the vehicle to a c c o m p l i s h the m i s s i o n objective under the most a d v e r s e s u r f a c e conditions. If the m a r i a 1 a r e a s prove to be quite favorable, being perhaps 90% acceptable to LEM, the verification approach is of l e s s e r importance. That i s , e i t h e r the a r e a sampling o r the point verification approach will provide the r e q u i r e d verification confidence. Even with t h i s favorable s u r f a c e , the point verification approach c a n increase the LEM probability f r o m 90% to n e a r l y 100% which m a k e s t h i s approach s u p e r i o r even f o r a good moon. 3 -52 V BSR 903 3200 H€Tflf) S F i g u r e 3 - 2 6 A r e a Sampling i n Terrain Containing L a r g e Unacceptable A r e a s V 3-53 BSR 9 0 3 If the lunar s u r f a c e proves to be quite a d v e r s e , s a y 40% unacceptable t o LEM, the gap between the two approached widens greatly. Even if a vehicle i s able t o sample lO0y0 of such a lunar s u r f a c e on a n a r e a ( s t a t i s t i c a l ) b a s i s , the s i t e m u s t be r e j e c t e d because only 60% is acceptable and EPD-98 is not satisfied. On the other hand, the point verification approach s t i l l r e s u l t s in a successful mission, with the acceptability of the verified s i t e approaching l O O y o in a n a r e a which overall is only 6OT0 acceptable. This i s illustrated in the example discussed in Section 3. 3. 3. F r o m the above discussion, i t a p p e a r s that e a r l y SLRV flights might well be operated in the a r e a sampling mode to c o v e r a l a r g e a r e a and t h e r e by refine our knowledge of the surface. F o r subsequent flights, the point verification approach a p p e a r s t o be s u p e r i o r in accomplishing LEM s i t e verification, since i t provides the maximum probability increment f o r a given surface. Thus, the bulk of the s t r a t e g y studies have been concent r a t e d on the point verification approach. The Point Verification s t r a t e g y will now be defined a s consisting of two parts: 1. 2. Point location determination (pattern layout) Point s u r v e y orientation. 3. 3 . 2 . 1 Point Location Determination Assume that the basic p a t t e r n t o be followed is a s shown in F i g u r e 3-1. This pattern will be followed in a clockwise m a n n e r a s shown. The pattern m u s t be tentatively located and o r i e n t e d following touchdown a s indicated in the upper right of F i g u r e 3-25 on the b a s i s of Surveyor p i c t u r e s taken during the landing phase. In principle, a n o v e r l a y of the p a t t e r n i s placed upon the Surveyor p i c t u r e t o d e t e r m i n e , b a s e d on the amount of detail available, the b e s t choice f o r : 1. 2. P a t t e r n location P a t t e r n orientation. Thus, the pattern i s moved Over the picture and a nominal choice m a d e on the b a s i s of such f a c t o r s a s the number of potential points lying in a r e a s BSR 903 which appear acceptable. goal f o r the mission. T h i s is the f i r s t point of strategy: setting the Once the m i s s i o n h a s begun, SLRV data become available a s indicated in F i g u r e 3-25. The next major point of s t r a t e g y is the p r o c e d u r e to follow upon encountering impassable a r e a s . Until s o m e data a r e available which d e s c r i b e the likelihood of saving distance by going in a c e r t a i n direction when encountering c e r t a i n surface f e a t u r e s , a simple rule m a y be used: t u r n s o as to minimize the departure f r o m the s t r a i g h t ahead d i r e c tion. The purpose of t h i s point of strategy is to follow geological formations i n the g e n e r a l direction of t r a v e l and avoid making t u r n s exceeding 900. . If, a f t e r a r r i v i n g at a tentative point location, it is found that the location is impassable o r unacceptable, the r u l e of s t r a t e g y is t o attempt t o r e l o c a t e the point on a line a t right angles to the straight-line l e g , on the side c l o s e s t to Surveyor. Both this r u l e and that d i s c u s s e d in the previous p a r a g r a p h a r e i l l u s t r a t e d i n Figure 3-27. The l a t t e r r u l e r e s u l t s in shrinking the p a t t e r n s i z e while rotating the point locations about the p a t t e r n c e n t e r ( a s s u m e d as Surveyor). Since the p a t t e r n is originally designed to provide minimum o v e r l a p while maintaining complete coverage by the c i r c l e s of LEM translational capabilities, t h i s shrinkage m e r e l y i n c r e a s e s the amount of o v e r l a p while d e c r e a s i n g the probability of s u c c e s s by r e a s o n of the lower overall verification radius. If a l t e r n a t e point locations w e r e t r i e d on the opposite side f r o m Surveyor, a t Point A of F i g u r e 3-27 it is quite likely that holes f r o m which LEM could not r e a c h a v e r i f i e d point would be l e f t in the coverage. The question naturally a r i s e s as t o how far t o d i s t o r t the pattern by moving a single point inward. Res u l t s t o date show that moving the point by 50% of the interpoint spacing (528 m ) is about the p r a c t i c a l limit. If a point cannot be found within t h i s d i s t a n c e , the point i s abandoned, and the next point s u r v e y is attempted. A s s u m e that point No. 6 of F i g u r e 3-1 is abandoned. When the SLRV is completing the next ring of points (14, 15, and 16 of F i g u r e 3-1), points 15 & 16 would then b e moved inward to partially f i l l the hole. It should be noted in passing that since surface m a p s have not yet been incorporated in t h e simulation, the decision a s t o whether to abandon a point is a r b i t r a r i l y s e t at a number ( p r e s e n t l y 4 ) of unsuccessful tr.ies.. However , as indicated above, the s t r a t e g y of whether to abandon a point is actually a question of how much p a t t e r n distortion will be p e r m i t t e d . V 3-55 BSR 903 ------ Actual Path and Point Locations Figure 3 - 2 7 Rules of Strategy 3-56 V 1 The question of holes o r voids in the p a t t e r n was mentioned b r i e f l y above. Holes will o c c u r i n actual m i s s i o n s p r i m a r i l y b e c a u s e of bad t e r r a i n and secondarily b e c a u s e of misjudgement as t o the acceptability of a p a r t i c u l a r point. That is, b e c a u s e of the amount of data t o be p r o c e s s e d t o make the acceptability decision, decision e r r o r s m a y quite possibly o c c u r . A point m a y initially be s c a r e d a s acceptable, only to prove l a t e r to be actually unacceptable. If the SLRV h a s completed the 19-point m i s s i o n , it m a y r e t u r n to find a good point where t h e e r r o r was m a d e . If, however, the m i s s i o n h a s been t e r m i n a t e d and the hole is then found to e x i s t , the s t r a t e g y is to move the LEM a i m point f r o m the c e n t e r of the p a t t e r n in a d i r e c t i o n radially opposite t o t h e hole. T h i s i s i l l u s t r a t e d i n F i g u r e 3 - 2 8 . The amount of the a i m point relocation is a function of the distance of the hole f r o m the c e n t e r of the pattern. Since a hole in the c e n t e r , w h e r e the highest percentage of LEM flights would land, is m o r e s e r i o u s than a hole on the p a t t e r n p e r i p h e r y , the relocation of the a i m point is a maximum when the hole is in the center and d r o p s off for holes at the p e r i p h e r y . The amount of t h i s relocation has not yet been computed.& It m a y become a p p a r e n t after s e v e r a l points have been examined that t h e a r e a chosen initially is not suitable f o r the p a t t e r n . T h u s , a s in the upper portion of F i g u r e 3-29, points 1 and 2 m a y have been v e r i f i e d , and e f f o r t s t o locate points anywhere in the l a r g e bad a r e a have failed. The p a t t e r n will then be moved t o the alternate position shown in t h e lower position. The points a l r e a d y verified now f o r m the o u t e r p e r i m e t e r of the p a t t e r n r a t h e r than the c e n t e r . The net r e s u l t is that m o s t of the points a l r e a d y v e r i f i e d m a y be u s e d in a second p a t t e r n and the SLRV p r o c e e d s t o v e r i f y the remaining points. Studies t o date have shown t h a t , i f bad s p o t s a r e comparable in s i z e t o the pattern s i z e to t h e p a t t e r n s i z e as i n F i g u r e 3-29, the p a t t e r n m u s t be moved. If bad spots a r e s m a l l e r , s a y of a s i z e c o m p a r a b l e t o the point s i z e , the p a t t e r n is not moved but is only d i s t o r t e d by m o v i n g the points. A s bad spots get v e r y s m a l l and v e r y d e n s e , the whole a r e a b e c o m e s unacceptable, and t h e LEM landing s u c c e s s probability is too low to attempt landing. The final i t e m in the point location s t r a t e g y is how to p r o c e e d when vehicle f a i l u r e s a r e imminent or have a l r e a d y o c c u r r e d , degrading p e r f o r m a n c e but not causing m i s s i o n abort. The stand taken h e r e is that the p o s s i b i l i t y of f a i l u r e s is p r o p e r l y the domain of p r o g r a m s t r a t e g y a s d i s c u s s e d i n Section 3 . 3 . 1. E a c h mission must be planned with the r e l i a b i l i t y prediction in mind. When p a r t i a l f a i l u r e s actually o c c u r during I V 3-57 BSR 903 Figure 3-28 L E M Aim Point Adjustment 3-58 BSR 903 Figure 3 - 2 9 Pattern Relocation V 3-59 BSR 903 a mission, the m i s s i o n should not be changed in concept but m e r e l y proceed a s planned, albeit a t a slower pace. It might s e e m t h a t , knowing a p a r t icular failure has o c c u r r e d , the remaining lifetime should be predicted and the measurement plan changed, e . g, to cover the maximum possible a r e a in the remaining time. However, within the p r o g r a m planning, a specific mission definition might c a l l f o r 13 points to be verified. If 13 points has been unequivocally defined a s the minimum r e q u i r e d before LEM will land, t h e r e is l i t t l e to be gained in changing the m i s s i o n to achieve a hasty look during the final m i s s i o n hours. A possible exception is t h a t , if the failure r e n d e r s 13-point verification impossible, the r e m a i n ing lifetime m a y be spent i n examining wider a r e a s of the lunar s u r f a c e t o add to general scientific knowledge. However, this is the domain of p r o g r a m s t r a t e g y and is not t o be decided upon except in detail a f t e r a f a i l u r e has actually o c c u r r e d on a given mission. 3.3. 2. 2 Point Survey Orientation One detail of o v e r - a l l s t r a t e g y which h a s not received too much attention, and justifiable so, is the orientation of the individual point s u r v e y p a t t e r n s . In p a r t i c u l a r , it is recognized that the point s u r v e y p a t t e r n c a n be oriented north-south, e a s t - w e s t , e t c . Each s u r v e y within a point will probably be oriented differently. Assuming that c r e v i c e detection capability as a function of incident illumination is known, the point s u r v e y p a t t e r n m a y be oriented to maximize safety a s the sun angle changes. Another f a c t o r in point survey orientation is the effect on navigation e r r o r s because of the orientation of the s u r v e y relative to Surveyor (for R F ranging). At the p r e s e n t time, the optimum orientation of the point s u r v e y h a s not been defined a s a function of all f a c t o r s in combination. T h i s is a portion of s t r a t e g y , however, and m u s t be defined a s t h e f a c t o r s and t h e i r effects a r e further defined. 3. 3. 3 Example of Mission Strategy A s an example of the application of the few s i m p l e r u l e s of s t r a t e g y of Section 3. 3. 2 , the. details of a 19-point m i s s i o n on a n a d v e r s e moon w i l l be discussed. It will be shown that the point v e r i f i c a t i o n approach permits a LEM landing on t h i s a d v e r s e s u r f a c e , w h e r e a s the sampling approach does not. The s u r f a c e is purposely a s s u m e d to be 40% "bad", where i s f o r simplicity defined as both i m p a s s a b l e f o r the SLRV and unacceptable to LEM. By choosing such a s u r f a c e , the possibility BSR 903 of verifying the a r e a by the a r e a sampling a p p r o a c h is outlawed by definition, since the r e q u i r e m e n t (EPD-98) s t a t e s that 7070 of the a r e a m u s t m e e t r e q u i r e m e n t s with 9970 confidence. Even with a vehicle capable of t r a v e r s i n g t h i s a s s u m e d s u r f a c e entirely and of sampling it 10070 ("bad" now defined as unacceptable to LEM), the a r e a m u s t still be r e j e c t e d f o r LEM landing, since only 6Oy0 of it i s good by definition. Yet, by using the point verification approach, the LEM may land on t h i s s u r f a c e with a p r o b ability of s u c c e s s of approximately 0.988 with 10070 confidence. A m a p of the s u r f a c e containing 4070 bad a r e a was c o n s t r u c t e d using the technique d i s c u s s e d in Section 3. 1 . 2 . 2 , under the heading " T i m e , Distance Relationships - Interpoint Travel". The m i s s i o n was then defined as verification of 19 points in the pattern of F i g u r e 3 - l ( a ) . It was a s s u m e d that t h e S u r v e y o r landing was in a good a r e a so a s not to penalize the SLRV f o r bad landings. A lso , since 4070 of the a r e a is bad, t h e p a t t e r n was initially positioned to give eight points (4270) in bad o r m a r g i n a l a r e a s . Placing t h e points in bad areas i s t h e s'me a.s a s s u m i n g that t h e p i c t u r e s taken during the Surveyor landing w e r e e i t h e r not r e c e i v e d o r did not p e r m i t recognizing t h e bad a r e a s . Starting f r o m point (1) then, the p a t t e r n was followed in a clockwise m a n n e r under the r u l e s of Section 3. 3. 2. In particular: 1. When avoiding h a z a r d s , turn s o a s to move as c l o s e to s t r a i g h t ahead a s possible. Move at right angles t o the last interpoint line and t o w a r d s Surveyor when s e a r c h i n g for a good point location. R e s t r i c t the distance t r a v e l l e d in (2) t o 5070 of the interpoint spacing and move t o the next point in the p a t t e r n . Fill in any holes c a u s e d by r e s t r i c t i o n ( 3 ) by a n inward shift of the points of the next outer ring. 2. 3. 4. F i g u r e 3-30 shows the r e s u l t s of applying t h i s s t r a t e g y to the 4070 bad s u r f a c e . The nominal p a t t e r n is shown in solid l i n e s ; the dotted l i n e s indicate the SLRV path. C i r c l e s defining the l i m i t s of LEM t r a n s l a t i o n a l c a p a b i l i t y have a l s o been shown t o indicate t h e coverage of the a r e a in the p r e s e n c e of the p a t t e r n distortion. Note that points 14 and 16 w e r e a b a n doned, b e c a u s e the SLRV could not find a r e a s o n a b l e path t o t h e m . Also, V 3-6 1 BSR 903 3-62 L BSR 9 0 3 point 19 was placed outward f r o m Surveyor leaving a hole in the pattern. By r e f e r r i n g t o F i g u r e 3-2, the probability of L E M landing on t h i s s u r f a c e is 0. 988, since the effective verified d i a m e t e r is about 1880 m e t e r s . Thus, it is seen that (even with a few s i m p l e r u l e s ) 17 points w e r e s u r v e y e d giving a probability increment of 0 . 3 8 8 o v e r the b e s t possible r e s u l t using a r e a sampling. I V 3 -63 BSR 903 SECTION 4 EVALUATION O F HEAVIER VEHICLES Section 3 p r e s e n t e d an evaluation of the 100-lb SLRV design. This section p r e s e n t s evaluations of vehicles up t o 150 lb in weight. Five designs a r e f i r s t s u m m a r i z e d , e a c h r e p r e s e n t i n g a reasonable design f o r the s t a t e d weight. These designs a r e d e s c r i b e d in detail in Volume 11, Section 6. T h e s e evaluations a r e b a s e d on simulation r e s u l t s using the p r o c e d u r e s followed i n the evaluation of the 100-lb SLRV. The p r i m a r y evaluation objective w a s to d e t e r m i n e the probability of s u c c e s s f o r the 19-point m i s s i o n . L e s s e r objectives w e r e t o d e t e r m i n e s u c c e s s probabilities f o r p a r t i a l m i s s i o n objectives and to define the achievable saving in m i s s i o n duration with the heavier v e h i c l e s . Evaluations for the b a s i c mission a r e given fii-at, fd?cv;ec! hy those for the adaptive m i s s i o n . 4.1 SYSTEM DESCRIPTIONS Table 4-1 p r e s e n t s in summary f o r m the vehicles which w e r e evaluated. F o r g r e a t e r detail s e e Section 6, Vol. 11. TABLE 4-1 SUMMARY OF HEAVIER VEHICLES System Weight (Ib) Obstacle Climbing Capability Weight Allocated to Re dundan cy Operating Speed (mph) 110 120 130 140 150 40 0 0.07 50 5 2 10 10 0.07 0. 18 0. 18 0. 18 60 70 100 V 4- 1 BSR-903 4.2 PROBABILITY OF MISSION SUCCESS 4.2. 1 Basic Mission The probability of m i s s i o n s u c c e s s f o r the b a s i c m i s s i o n with heavier v e h i c l e s is given in F i g u r e 4-1. The 100-lb curve is a l s o shown for comparison. Only the 110- and 150-lb s y s t e m s a r e shown, since these a r e sufficient to show the extent of the i n c r e a s e . With the addition of 10 lb to the 100-lb s y s t e m , a g r e a t i n c r e a s e in Ps is achievable. The i n c r e a s e i n adding another 40 lb (150 total) is l e s s i m p r e s s i v e . The 110-lb s y s t e m shows this disproportionately l a r g e improvement because the 110-lb operation is b a s e d on a 24-hour DSIF availability ( 3 s t a t i o n s ) w h e r e a s the 100-lb operation w a s l i m i t e d to an 11-hour day consistent with the single 210-ft DSIFd'ish. The probability of s u c c e s s achieved as a function of s y s t e m weight is shown f o r both the minimum (13 point) and d e s i r a b l e (19 point) m i s s i o n in F i g u r e 4-2. F o r both m i s s i o n s i t is s e e n t h a t the g r e a t gains a r e to be m a d e by adding 20 t o 30 lb t o the 100-lb s y s t e m . F o r higher weights, the gains a r e not as significant. It would s e e m that with a s y s t e m weight of 120 to 130 lb, the m o s t significant gains to be made t h e r e a f t e r would be as the r e s u l t of s t r a t e g y ; > i n p a r t i c u l a r , optimizing the p a t t e r n to be followed. An i n t e r e s t i n g study w a s made to evaluate the mobility benefits of allocating weight allowances above 100 lb. With all p a r a m e t e r s of the 100-lb vehicle remaining fixed, the simulation w a s run f o r i n c r e a s i n g mobility capability. The r e s u l t s a r e shown in F i g u r e 4-3. On the No. 1 s u r f a c e model, no i n c r e a s e i n s u c c e s s probability w a s achieved, which is as expected: the probability of s u c c e s s f o r this model is not l i m i t e d by mobility capability of 30 cm, but mainly by s y s t e m reliability. Conversely, No. 8 s u r f a c e model shows s o m e improvement above 30 cm. However, this improvement is not l a r g e c o m p a r e d to the value obtained by the 30-cm design. It may be argued that the r e s u l t s of F i g u r e 4 - 3 a r e s t r i c t l y dependent upon the surface models a s s u m e d . As the s u r f a c e m o d e l s a r e m a d e m o r e rugged, the c u r v e s w i l l get correspondingly s t e e p e r , reflecting g r e a t e r advantage in higher mobility. The p r o b l e m i n s y s t e m optimization, however, is to s e l e c t a mobility capability r e p r e s e n t i n g a r e a s o n a b l e t r a d e - o f f between the s u r f a c e expected and the weight allocation. F o r the s u r f a c e m o d e l s a s s u m e d , this has been accomplished i n the 100-lb design at 30 cm. At higher weights, choice of the optimum mobility capability m u s t a w a i t f u r t h e r definition of s u r f a c e models as well as s y s t e m r e q u i r e m e n t s . 4-2 BSR 903 I I ! ' i i , f , - ' ' , 4-3 BSR 903 Figure 4 - 2 Probability of Success f o r Heavier Vehicles Basic Mission 4-4 V BSR 903 . ' " 1 i * i ; ' I + i . . . I 2 7 /--+--- E& 8 i T. i I . . . -t-. i - I . -. .... ,. \ j I i ---I---- ' e t I ~. t I i , . ... I i . . . ! . , I --e 1 1 IP i 3v S L ~ V Ir 0 70 1 ? I n I ! . _ pabililty Figure 4-3 Effect of SLRV Irregularity Capability V 4- 5 BSR-903 4. 2. 2 Adaptive Mission The adaptive m i s s i o n w a s conceived to improve o v e r the b a s i c m i s s i o n by taking advantage of favorable t e r r a i n in the m o r e r a p i d completion of m i s s i o n tasks. The i n c r e a s e in s u c c e s s probability f o r the 100-lb vehicle w a s shown i n Section 3. The gains achievable with h e a v i e r vehicles a r e given i n Figure 4-4. This may be compared with the b a s i c m i s s i o n by r e f e r r i n g to F i g u r e 4-1. F o r the 19-point m i s s i o n the adaptive approach shows the following probability i n c r e m e n t s : Weight 100 110 150 I n c r e a s e i n Ps 0.09 0.10 0.06 % Increase 30 29 14 The probability of s u c c e s s as a function of s y s t e m weight is given i n F i g u r e 4-5. As w a s shown for the b a s i c m i s s i o n , s y s t e m weights beyond about 130 lb show little r e l a t i v e gain. 4.3 MISSION DURATION 4. 3. 1 Basic Mission The m i s s i o n duration f o r the b a s i c m i s s i o n s (both 19 and 13 point) is shown in F i g u r e 4-6. The l a r g e d e c r e a s e i n m i s s i o n t i m e f r o m the 100-lb s y s t e m to 110 lb is caused by the switchover f r o m the 11-hour to 24-hour operation as mentioned i n Section 4.2. 1 The o b s t a c l e capability and the redundancy a r e steadily i n c r e a s e d i n going f r o m 110 to 120 l b and up to 150 lb. Thus m i s s i o n duration falls consistently as shown. S y s t e m weight of 120 to 130 l b r e s u l t s in r e a s o n a b l e m i s s i o n d u r a t i o n s of l e s s than t h r e e months. Increasing the weight still f u r t h e r d e c r e a s e s the m i s s i o n t i m e l e s s rapidly. T h e r e f o r e , a weight in the neighborhood of 120 to 130 lb m a y be ample. I 4. 3. 2 Adaptive Mission Mission duration f o r the adaptive m i s s i o n with h e a v i e r S L R V ' s is shown in Figure 4-7. Comparing t h e s e r e s u l t s with the b a s i c m i s s i o n of F i g u r e 426:shoWS a . , r a t h e r cbnsistknt ' i a v i n g of:one rhonth f o r all s y s t e m weights f o r the 19-point m i s s i o n . The saving f o r the m i n i m u m m i s s i o n of 13 points is proportionately lower. V BSR 903 V 4-7 BSR 903 F i g u r e 4L-5 Probability of Success f o r Heavier Vehicles- Adaptive Mission 4-8 V ~ BSR 903 I I ll 1 . I I I I I I I I I I I I O I I I I I I I I 1 I A I l l I I I I I A I A> L ? I I I I ! I I I I i I I I i i I I I t-~-t i 1 I I I I I I I I , + F i g u r e 4-6 Mission Duration for Heavier Vehicles -Basic Mission V 4-9 BSR 903 F i g u r e 4-7 Mission Duration f o r Heavier Vehicles-Adaptive Mission 4- 10 V BSR 903 The variations in m i s s i o n duration as a function of the eight s u r f a c e models a r e shown f o r the heavier vehicles i n F i g u r e s 4-8 through 4-12. The steady d e c r e a s e i n m i s s i o n t i m e with added weight can be s e e n for any model f r o m t h e s e figures. Note that No. 4 s u r f a c e model shows the b e s t possible m i s s i o n t i m e . This model i s flat, smooth, and soft and gives the m o s t optimistic t i m e . Adverse slopes o r o b s t a c l e s a r e not encountered, and it is a s s u m e d that no crevices e x i s t i n the soft soil. The model t h e r e f o r e m a y be likened t o a flat d e s e r t a r e a . V BSR 903 $1a Q) 1 I 2 ' i u d v) 5 -3 4- 1 I 1 1 -5 6 6 J 8 1 b 1 7 8 AVfRAGC R - 1 1 F i g u r e 4 - 8 Mission Duration- 110 lb System 4- 12 V I 2 4 3 a u Q) Q) g d k + 5 w I V I ' 6 7 Q AVER4 CE Mission Duration (Months) F i g u r e 4-9 Mission Duration- 120 lb System V 4-13 BSR 903 0 I 2 3 4 5 Mission Duration (Months) F i g u r e 4 - 10 Mission Duration- 130 lb S y s t e m 4- 14 V -1 : -2 d 1 1 a Q) 0 W 2 : 5 6 3- 3 45 6 J - 7 1 , I 1 7 D 8 AI/€RAGf -I 1 Figure 4- 1 1 Mission Duration- 140 lb System 4-15 V BSR 903 1 2 Mission Duration (Months ) Figure 4 - 1 2 Mission Duration- 150 lb System V .. BSR 903 SECTION 5 ENGINEERING TEST MODEL TEST RESULTS The objective of the Engineering T e s t Model (ETM) w a s to demons t r a t e mobility, maneuverability, the principle of a floating pivot point, and limitations imposed upon mobility by the amount of power available. The problem of scaling a test vehicle f o r e a r t h ( e . g. , d e m o n s t r a tion of a design f o r operation on the moon at 1 / 6 e a r t h g) w a s solved by using a 1:l scale f o r linear dimensions and m a s s . The choice of t h e s e n s c a l e f a c t o r s r e s u l t e d i the requirement to s c a l e t i m e in the r a t i o of l:&-such that r e a l - t i m e i n the t e s t s r e p r e s e n t e d only l/&- r e a l - t i m e on the moon. Accordingly, a 3 perfomanca c h a r a c t e r i s t i c s involving t i m e such as power, velocity, accelerations, etc. , w e r e m e a s u r e d i n the a p p r o p r i a t e scale ratio. ETM is illustrated i n F i g u r e s 5 - 1 and 5 - 2 , and can b e d e s c r i b e d b r i e f l y as follows: 1 A n e 1. 4 - t r a c k vehicle T r a c k s approximately 2 3 in. long by 3 in. wide T r a c k a t t a c h m e n t point - The t r a c k s a r e attached to the s t r u t s by m e a n s of an axle and strike plate which allows each t r a c k t o b e locked a t 00 o r +450 with r e s p e c t to t h e s t r u t o r f r e e floating between stop l i m i t s ( s t o p s at either +30° o r +45O) T r e a d - 0. 25 inch s i l a s t i c (foamed silicone r u b b e r ) bonded t o m e t a l r i m Track base 2 . 3. 4 . 5. - 20 in. (between c e n t e r of s t r u t s (outside-to-outside of t r a c k , 6. T r a c k spacing pairs) - 28 in. V 5-1 BSR 903 5-2 BSR 903 ... . F i g u r e 5 - 2 F r o n t View, E T M V 5-3 BSR 903 7. 8. Body length Body width Body height - 38 in. (2 sections, 19 in. each) 11 in. 8 in. 9. 10. 11. Ground c l e a r a n c e of body - 12 in. D r i v e - individual t r a c k (friction d r i v e ) furnished by m o t o r g e a r head a s s e m b l y Vehicle s p e e d s - o p e r a t o r selection of speeds l i s t e d below f o r manual control. Automatic mode u s e s V1 for f o r w a r d o r r e v e r s e , a combination of V1 and V2 o r V1 and 0 to initiate t u r n r a t e , and V1 and V2 f o r steady-state turn. 12. V1 = 0. 396 mph V2 = 0 . 2 6 mph V 3 = 0 . 0 7 4 mph 13. Turn r a d i u s state t u r n - 5 ft. to center of body in steady- 14. Turn r a t e - variable, selected by o p e r a t o r on control console 15. ETM Weight - 77. 25 l b (92 lb including b a l l a s t ) . A photograph of the ETM control console i s shown i n F i g u r e 5-3. F i v e m a j o r s u b a s s e m b l i e s w e r e integrated into the single enclosure: control and display panel, signal conditioner panel, a u t o m a t i c control panel, DC power supply, and the AC power control equipment. The c o n sole interconnects with the ETM vehicle and s t r i p c h a r t r e c o r d e r through an a c c e s s cable entry panel a t the r e a r of the console. 5-4 V BSR 903 F i g u r e 5 - 3 ETM Console A s s e m b l y V 5 -5 BSR 903 5 . 1 TEST COURSE DESCRIPTION The t e s t c o u r s e used f o r engineering t e s t s consisted of four 16 x 16 ft wooden decks, two 4 x 12 f t wooden decks, a n adjustable s t e p obstacle, dome-shaped obstacles, a n d a n obstacle c o u r s e consisting of random s i z e r o c k s f r o m 15 to 30 cm. in diameter. T w o of the 16 x 16 f t d e c k s w e r e p r o vided with various covering m a t e r i a l s ranging from b a r e plywood through a sheet aluminum to obtain data on various f r i c t i o n coefficients. One of the two decks w a s adjustable in a n angle up to 45O to allow evaluation of the ETM on slopes and obstacles on slopes. The other p a i r of 16 x 16 foot d e c k s w e r e joined together with one of the decks capable of being tilted to a maximum inclination of 35O. T h e s e decks w e r e bounded with a 2-foot high fence and filled to a depth of 12 inches with expanded P e r l i t e at a nominal density of '7. lb / ft 3 . . This m a t e r i a l had p r o p e r t i e s somewhat m o r e c r i t i c a l i n t e r m s of vehicle design than the minimum "soft soil" model specified in EPD-98. A description of the c h a r a c t e r i s t i c s of the P e r l i t e is contained i n Table 5-1. E x a c t scaling of the soil was not possible b e c a u s e of the non-linear relationship between the b a s i c soil p a r a m e t e r s . Expanded P e r l i t e w a s chosen to m a t c h the m o r e c r i t i c a l p a r a m e t e r s of sinkage and cohesion coefficient of the softsoil model. Variation in the sinkage exponent (n) f r o m the ideal s c a l e value did not m a t e r i a l l y affect the t e s t s , since the total sinkage of the vehicle was limited to approximately 1 inch. TABLE 5 - 1 SOIL PARAMETERS ~~~ ~~ - I Parameter Sinkage coefficient (k) Sinkage exponent ( n ) Grain s i z e m i c r o n s Cohesion coefficient ( c ) Angle of internal friction (q,) Lunar Scale ~ Perlite ~ 0. 083 p s i 1 50 0. 5 p s i 1 0. 39 f . 0 3 p s i 0.58 2 . 0 1 50 0-3 psi 200 to 35O 700 (average) 0 to 0. 5 20° to35O 0. 012 p s i 29O t o 32O V BSR 903 5.2 TEST RESULTS 5. 2. 1 Mobility The vehicle motion could b e controlled on the h a r d s u r f a c e with various combinations of t r a c k speed and direction; but, on t h e soft soil, b e s t control w a s accomplished by varying the speed of the t r a c k s while they all d r o v e i n the s a m e direction. The vehicle could b e turned with a five foot r a d i u s ( t o center of body) on a h a r d s u r f a c e with slightly b e t t e r performance in the soft soil. A scuff t u r n could b e accomplished within the length of the vehicle on the h a r d s u r f a c e by operating the inside t r a c k s i n r e + e r s e and the outside t r a c k s in f o r w a r d . The maximum slope that the vehicle could c l i m b w a s 35O on a plywood s u r f a c e , and 180 on the 7 lb/cu. ft. p e r l i t e soft soil. The angle of r e p o s e of the p e r l i t e on the t e s t course w a s 2 6 O which limited the soft s o i l slope climbing capability. Above 18O the f o r w a r d motion of the vehicle w a s marginal, although the t r a c k s w e r e n o t exceeding the power l i m i t s , and t h e r e f o r e continued to turn. The ETM vehicle s t a t i c stability l i m i t s w e r e 80° in pitch and 4 Z 0 roll. 5.2.2 Step T e s t The r e s u l t s f r o m the step t e s t have been plotted i n F i g u r e 5-4. The p e r l i t e s t e p w a s f o r m e d using wood f o r a r i s e r . 5.2. 3 Knife Edge T e s t T e s t s w e r e conducted with a 314" thick obstacle so that the front t r a c k s would c l i m b o v e r the obstacle and w e r e driving on the f l o o r b e f o r e the r e a r t r a c k s s t a r t e d to climb the obstacle. The vehicle would climb o v e r a 30-cm knife edge obstacle of plywood o r roofing p a p e r , and in the p e r l i t e it would climb o v e r a 15-cm wood obstacle. 5. 2. 4 C r e v i c e T e s t The r e s u l t s f r o m the c r e v i c e t e s t s a r e p r e s e n t e d in both tabular and plotted data, F i g u r e 5-5 and Table 5-2. V 5-7 BSR 903 Figure 5-4 E T M T e s t Results of Step-Climbing Capability 5-8 V ~- BSR 9 0 3 F i g u r e 5 - 5 ETM Crevice-Crossing Test Results on Roofing P a p e r Surface V 5 -9 BSR 903 TABLE 5-2 CREVICE TESTS ( A l l Distances in Centimeters) Test Course Surf ace Roofing Paper Crevice Oo (Pi ned) Approach 3ir E tion &30° (Stops) Angle ( O ) ?w d Rev :rossed ?ailed bossed Tailed 43 43 58 58 - ( ;ops ) t45O k o s s e d Tailed 20 18 30 23 33 28 28 30 25 23 32 26 30 27 27 28 23 22 20 32 25 35 30 30 32 27 25 34 28 32 29 29 30 25 21 30 30 X X 41 41 4 5 4 5 60 60 90 90 Plywood X X 56 56 58 58 56 56 52 52 57 57 58 58 56 56 47 47 57 57 61 28 18 33 37 35 32 28 28 32 32 33 32 30 20 35 39 38 34 30 30 34 34 35 34 34 34 31 31 X X X X 60 60 58 58 54 54 59 30 30 X X 45 45 X X X X 59 60 60 58 58 49 60 60 90 32 32 29 29 25 20 32 30 33 32 X X X X X 90 Alum inun 30 30 45 45 60 60 90 90 49 59 27 22 19 34 30 33 30 29 28 X X X X 59 63 63 58 58 - 34 32 35 34 32 30 36 32 35 32 61 - - X - 56 56 30 28 31 30 5-10 V BSR 903 5. 2 . 5 T r a c k Abort T e s t The ETM w i l l operate on t h e hard s u r f a c e scuffing one t r a c k , but not in the soft soil-where the t r a c k tends to dig in. With one t r a c k f r e e wheeling, the ETM o p e r a t e s satisfactorily on the hard s u r f a c e (both level and slope) and the level perlite. It would climb m o s t 12-cm o b s t a c l e s on a h a r d s u r face. With two t r a c k s f r e e wheeling, the vehicle operation w a s m a r g i n a l and difficult t o predict. 5. 2. 6 Random Obstacle T e s t The ETM p e r f o r m a n c e in the random obstacle t e s t (consisting of a pile of r o c k s ranging i n s i z e f r o m 16 to 30-cm i n d i a m e t e r ) c a n only b e evaluated subjectively due to the random n a t u r e of the course. It w a s o b s e r v e d that s t e e r i n g on steep slopes (15 to 30°) w a s difficult; the vehicle tended t o follow a path of l e a s t resistance. Inclusion of a t u r n actuator might improve t h e cperation: however, the gain v s the i n c r e a s e in weight f o r the actuator h a s not been thoroughly evaluated. 5. 2. 7 P o w e r Limitations P o w e r limiting c i r c u i t s w e r e used to step the ET-M whenever the t r a c k m o t o r s exceeded the value scaled f r o m the SLRV (the power scaling f a c t o r i s 6 6 . As expected, t h e s e l i m i t e r s prevented climbing, at the highest speed (V1)$ slopes above 20° and maximum step obstacles. T h e s e t e s t s w e r e accomplished at lower speeds (V2 and V3). Power to the t r a c k m o t o r s of the ETM w a s supplied through speed control units duplicating, in m o s t r e s p e c t s , t h e pulsating DC equipment planned f o r the SLRV. The t e s t r e s u l t s verify the feasibility of this technique. 5. 3 ETM MOBILITY EXTRAPOLATIQN The p a r a m e t r i c data used in Volume I1 f o r selection of the mobility concept included e s t i m a t e s of system weight f o r higher step-climbing capability. T h e s e e s t i m a t e s w e r e based on a compatible design providing equal mobility under all design conditions, i. e. , u n d e r c a r r i a g e clearance, l a t e r a l stability, s t e p s , and crevices. T h e p a r a m e t r i c study indicated the superiority of a four - t r a c k design in the weight r a n g e o f i n t e r e s t f o r the 100-kb SLRV. B e c a u s e of weight c o n s t r a i n t s , a n allocation of only 18 lb w a s m a d e and a t a r g e t of 30-cm step V 5-11 BSR 903 climbing capability w a s s e t f o r the design of the mobility s u b s y s t e m . The . a c t u a l values achieved by this design w e r e 12. 9 l b and approximately 40 cm (as demonstrated by the ETM). F o r purposes of comparison, it should be noted that the p a r a m e t r i c study included interconnecting s t r u c t u r e ( s t r u t s ) a s p a r t of the mobility s y s t e m weight, i n addition to the weight of the t r a c k s , d r i v e m e c h a n i s m , i d l e r s , etc. T h i s addition (1. 44 lb f o r the p r e s e n t design) r e s u l t s in a c o m p a r a b l e figure of 14. 3 lb. F u r t h e r m o r e , the p r e s e n t design i s not "compatible" i n that it provides only 30 c m of u n d e r c a r r i a g e c l e a r a n c e and l e s s than 40 c m l a t e r a l stability (depending on cg height). The c r e v i c e c r o s s i n g capability, with t r a c k s floating r a t h e r than pinned, i s slightly l e s s than 30 c m . T h e r e f o r e , the s t r u t s w i l l have to b e m a d e longer and controllable t r a c k locks added to m a k e the p r e s e n t design compatible at 40 cm. T h i s philosophy can be u s e d to e x t r a p o l a t e f r o m the p r e s e n t design (validated by E T M t e s t s ) to h e a v i e r S L R V configurations with i n c r e a s e d mobility o r a g r e a t e r allocation of weight to mobility in the 100-lb s y s t e m , but a t the s a c r i f i c e of o t h e r s y s t e m capabilities. F i g u r e 5 - 6 shows the f o u r - t r a c k data f o r such a n extrapolation. The dotted c u r v e is the p a r a m e t r i c t r e n d used i n the o r i g i n a l s y s t e m concept selection. The l o w e r solid c u r v e shows r e v i s e d data b a s e d on subsequent design and t e s t i n f o r mation f o r a compatible design. It d o e s not a p p e a r n e c e s s a r y to provide m o r e than 50-cm u n d e r c a r r i a g e c l e a r a n c e f o r vehicles with g r e a t e r step-climbing capability b e c a u s e such h a z a r d s m a y be detected and avoided by r e a s o n a b l e o p e r a t o r control. T h e r e f o r e , a n upper solid c u r v e i s p r e s e n t e d f o r l i m i t e d d e s i g n s having only 50-cm u n d e r c a r r i a g e c l e a r a n c e and equivalent l a t e r a l stability. These c u r v e s include a n e s t i m a t e of t h e weight r e q u i r e d f o r folding the s t r u t s to fit i n the Surveyor envelope when the dimensions of the p r e sent (100-lb) design a r e exceeded. No c o n s i d e r a t i o n i s given to t h e r e l i a bility of such joints in the extrapolation a n a l y s i s . The application of t h e s e c u r v e s i s i l l u s t r a t e d by a n example. To find Ihe effect on mobility system weight f o r a change i n mobility r e q u i r e m e n t s , a s s u m e that a 75 -cm step-climbing capability i s s e l e c t e d in conjunction w i t h a 50-cm u n d e r c a r r i a g e c l e a r a n c e . The c o r r e s p o n d i n g point on the l i m i t e d design curve gives a mobility s y s t e m weight of 32. 5 lb, a p p r o x i m a t e l v 18. 2 lb m o r e than the p r e s e n t design. 5-12 . V BSR 903 F i g u r e 5 - 6 F o u r - T r a c k Vehicle Mobility Extrapolation V 5-13 BSR 903 Based on E T M t e s t r e s u l t s , it i s anticipated that such a f o u r - t r a c k design i s f e a s i b l e . If t h e r e w e r e no changes in other s u b s y s t e m s , the SLRV would weigh 109. 9 lb, plus the 8. 3 lb Surveyor-mounted equipment allowance. Other weight changes might b e encountered; e. g . , i n c r e a s e d s t r u c t u r e a n d deployment support equipment f o r the heavier S L R V . However, it i s also possible that compensating reductions ( t r a d e - o f f s ) could b e m a d e in communications o r navigation equipment. The power r e q u i r e m e n t s f o r i n c r e a s e d mobility should h e noted Values indicated on the extrapolation c h a r t yield an e s t i m a t e of 17. 5 w a t t s f o r the 75-cm limited design, i f the top speed of 0. 16 mph i s maintained, "> * A . E S i n c r e a s e of 9. 5 w a t t s o v e r the r e f e r e n c e design would call f o r a power Y supply w e i g h t i n c r e a s e of approximately 5 lb. " Thus, the extrapolation c h a r t provides a m e a n s of i n t e r p r e t i n g the ETM t e s t r e s u l t s i n t e r m s of l a r g e r vehicles, w h e r e l a r g e r e f e r s to the s c a l e of the mobility s y s t e m . I4