Manual control

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					  Manual control
   of the Mercury spacecraft
  The Astronaut will manually control Mercury as a normal part
  of his flight program and may explore his capabilities in man-
  ual control of spacecraft through several critical maneuvers

  By Robert B. Voas
  NASA MANNED SPACECRAFT CENTER                                                       1




                                              HE Mercury      flight begins and ends with periods during which the
                                                 Astronaut does not control the vehicle’s attitude and flight path.
                                            During the launch, trajectory and attitude control come from the
                                            booster guidance system and the ground control center. Landing
                                            occurs passively by means of parachutes.
                                               The lack of manual control during these two phases of the mission
                                            has led to an underestimation of the Astronaut’s role in controlling
                                            the attitude of the Mercury spacecraft, It should be remembered
                                            that the pilot may elect to take full control over the attitude of the
                                            vehicle any time from separation of the booster through orbital
                                            flight, retrofire, and re-entry. During this period, there are four
                                            tasks which face the Astronaut: Control of attitude in orbit, control
                                            of attitude during retrofire, rate damping during re-entry, and re-
                                            covery from tumbling maneuvers.
                                               Control of attitude in orbit involves bringing the vehicle to a de-
                                            sired attitude in reference to the earth. The normal flight attitude
                                            for the capsule is - deg pitch (small end pointed down) and
                                                                    34
                                            0 deg roll and yaw. Should he wish to vary this attitude, the Astro-
   Robert B. Voas is Astronaut Training     naut can usually make the maneuver in a single axis at a time. Vary-
   Officer for the NASA Space Task          ing attitude in orbit is relatively simple if high tolerances in holding
   Group, and has played an important
   role in the design and development       a given attitude are not required. Such a maneuver is relatively
   of simulators for the Mercury pra-       easy because it can be done a single axis at a time and because time
   gram. Dr. Voas received a Ph.D.          is usually not a critical factor. The primary problem in learning to
   in psychology in 1953 from the Univ.
   of California at Los Angeles. After       do maneuvers effectively is to control so as to use a minimum amount
   serving with the Navy at the School       of fuel.
   of Aviation Medicine, Pensacola, Fla.,       The most critical maneuver for the Mercury Astronaut is control-
   where he was involved in research on
   selection and training of pilots, he     ling the vehicle during retrorocket firing. Three retrorockets are
   joined the Space Task Group in Octo-     ignited 5 sec apart and burn for 12 sec each, producing a variable
   ber 1958 and assisted the Project         deceleration pattern during the 22-sec retrofire period. Due to un-
   Mercury management in the selection
   of the Astronauts. During the past        certainties in the center of gravity and retrorocket alignment, torques
   two years, Dr. Voas has been coor-        about the major axes of the vehicle may be produced. These torques
   dinating the program which has            are difficult to estimate, but it is expected that 95% of the time they
   brought the seven Mercury Astro-
   nauts to a high level of proficiency,     will not exceed two-thirds of the control thrust available. Since high
    and is presently concerned with the      torques are developed and they are variable through the 22-sec
   program to maintain this high level       period of retrofire, rapid and accurate responses are required to keep
   of proficiency throughout the period
   of Mercury manned flights.                the vehicle under control.


18 Astronautics / March 1962
                               Control Systems in the Project Mercury Spacecraft


                                                                                   W I NDOW
                                                                                   RATE AND A T T I T U D E I N D I C A T O R S


        REFERENCE

                                                           1,  I
                                                                                   P E R I SCOPE



                                                                                                                         @ RATE GYROS
   ACCELLERATI ON        a                                                                                          &3
       SW I TCH


""""_                                      """"                                                                              """




                                    [%         AMPL I F I ER CAL 1 BRATOR
                                                                                                                             RATE DAMPER BOX
                                      I
                             AUTO- P I L O T MODE

                                                                              MANUAL P R O P O R T I ONAL
                                                                                     MODE                 RATE COMMAND MODE
   ""                        """                                                                                         """"


                                                    J



                               AUTOMATIC R E A C T I O N
                                 CONTROL S Y S T E M                                               NMJUAL REACT1 ON
                                                                                                    CONTROL SYSTEM


                             Summary of Project Mercury Trainers in Attitude Control

                                          Control Modes            Reference Systems               Types of Tasks
                                                                                                                            Environmental
                                                                                                                             Conditions     -1

                   Trainer




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                                                                                     I
                                                                                                     c
                                                                                                     d
          Procedures Trainer*                 X     X      X       X          X      X     X          X
                                                                                           -
         ALFA                         X       X                    X X        X      X        X       X
                                    -        -                     --
          Mastif                      X                            X
          Centrifuge*                 X                            -
                                                                   X
         * Can be used while performing other tasks.


                                                                                                          March 1962 / Astronautics 19           i
            A third task is the damping of oscillations of the         Three-Axis Side-Arm Controller
         Mercury spacecraft during re-entry. It is stable only
         in the blunt-end-forward attitude during the re-                 r L O C K PIN
         entry, and oscillations about the basic front-end-
         forward position occur unless it is perfectly aligned
         throughout re-entry. The Astronaut’s task is to
         damp out these oscillations. Since the frequency
         and amplitude of the oscillation vary throughout re-
         entry, re-entry rate damping could be a difficult task
         on a vehicle with low stability. However, wind-
         tunnel data and flight experience to date indicate
         that the re-entry stability of the Mercury spacecraft
         is high, perhaps high enough to re-enter successfully
         without a control system. Training experience has
         indicated that, at levels of stability demonstrated by                 LINKAGE          6
                                                                             YAW C O N T R O d -‘,
                                                                                                  7        LROLL
                                                                                                               CONTROL
                                                                                                              LINKAGE
         the spacecraft, the damping of oscillations is a rela-                                      YAW
          tively simple task for the pilot.
             Finally, the Astronaut must be able to recover
          from a tumbling maneuver. Tumbling of the Mer-
          cury vehicle is very unlikely, but it could result from   “Early Development of a Vehicle Attitude Display
          unusual torques produced by separation from the           and Control” ( ARS Preprint 1400-60). This system
          booster or by one of the reaction control jets freez-     gives alternative modes of flight control, described
          ing in an open position. In the event of tumbling,        by the illustration on page 19. There are two com-
          the Astronaut must first bring the vehicle to a sta-      pletely independent control systems-an automatic
          tionary position, reorient to the earth, and then cage    system, having a pair of high- and a pair of low-
          and reset his attitude gyros to restore his instrument    torque reaction jets for each axis, and a manual
          attitude reference.                                       system with a single set of proportional reaction jets.
             To accomplish these four functions, the Astronaut      Each of these systems has its own fuel supply and
          has available to him a complex but flexible control       controls so that they are completely redundant.
          system, described by Senders and Lindquist in                                         (CONTINUED ON PAGE 34)




                                                                                             Mercury Astronaut M. Scott Car-
                                                                                             penter operates controls inside
                                                                                             Procedures Trainer. Note the
                                                                                             window just above his eye level.
                                                                                             The view through the window can
                                                                                             be used as a reference in manual
                                                                                             control of the spacecraft.




il l   20 Astronautics 1 March 1962
Mercury Spacecraft                           In this way, the Astronaut can achieve   must be determined by the drift of
                                             double authority for difficult retrofire terrain across the face of the scope,
(CONTINUED FROM PAGE      20)                problems. All three manual control       This is a more difficult problem, since
                                             systems, whether operated singly or      a pattern of clouds or terrain must be
    When the Astronaut wishes to exer-                                                visible below the vehicle. At night,
                                             in combinations, are operated through
cise manual control-and he will as a         the single, right-hand side-arm con-     over unpatterned cloud cover, or over
normal part of all flights-he has ac-        troller, shown on page 20. This is a     the oceans when no clouds are pres-
cess to both control systems. He can         three-dimensional controller giving      ent, drift may be difficult to deter.
fly through the automatic control sys-       pitch thrust by a fore or aft movement,  mine. Furthermore, small rates in
tem, using the “fly-by-wire’’ mode of        roll thrust by a side-to-side movement,  pitch and roll can confuse the deter-
manual control. In this mode, he has         and yaw thrust by a twisting move-       mination of yaw, since they produce
an on-off control over the high- and         ment.                                    apparent drift. Despite these prob-
low-torque jets of the automatic con-            The Astronaut has available to him   lems, it appears likely that fairly fre-
trol system. A deviation of the con-         three major attitude reference sys-      quent checks of yaw will be possible.
trol stick one quarter of the full throw     tems. His primary display consists            The yaw-reference problem has two
turns on the low-torque jets, and three-     of a LABS indicator, modified to show    aspects: The initial heading deter-
fourths of the full throw actuates the       rates about the three capsule axes.      mination using terrain drift, and, sec-
high-torque jets.                             Capsule attitude is displayed on three   ondly, the maintenance of yaw posi-
     In addition to this access to the        separate indicators, placed around the  tion during retrofire, which must be
automatic control system, the Astro-          rate indicator, on the panel directly    done by observing rotational move-
 naut may use two modes of control            opposite the Astronaut’s head. This      ments of the earth in the periscope.
through the manual-control-system             display system was developed on the      For this latter purpose, there must be
jets. The first of these, the “Manual         basis of simulation studies which in-    some patterned terrain, such as a coast
 Proportional” mode, makes use of a           dicated that the well-trained pilot      line, which the Astronaut can use for
 set of mechanical linkages to open           primarily used rate information to con-  heading reference. Such a reference
 valves on the reaction jets by an            trol the retrofire.                      may not always be available where
 amount proportional to the deviation                                                  the retrofire maneuver must be initi-
 of the stick. A second control system       External References Used                  ated.
 making use of the manual jets is the                                                      Another problem with the use of
 “Rate Command” mode. In this                   Two systems of external reference      the periscope is the unusual view of
 mode, electrical outputs from the PO-       are available to the Astronaut. The       the earth which it provides. This
 tentiometer attached to the stick are       first of these is the periscope, which    produces some negative transfer to
 fed into a logic system which receives      gives him a nadir view of the earth       the control problem. Since the view
 information from its own set of rate        below the capsule. Through the peri-      is perpendicular to, rather than
 gyros. Through this system, signals         scope, the earth appears as a ball        parallel with, the earth‘s surface, some
 are sent to the manual-control-system       that can be centered by reference          initial confusion in roll and yaw con-
 solenoid valves; this gives a capsule       lines to determine the earth vertical.     trol with reversals of control have
 rate proportional to the deviation of       This provides a good reference in          been noted during training. How-
 the hand controller.                        pitch and roll. Yaw, or heading angle,     ever, with training, such reversals have
      Thus, the pilot has available to him                                              been eliminated.
 three major manual control systems:                                                        A second method of external refer-
 An on-off, fly-by-wire mode operat-                                                    ence is the capsule centerline win-
 ing through the automatic control jets;                                                dow. Through this window, the pilot
 a proportional acceleration control                                                    has a view of a small portion of the
 mode; and a proportional rate control                                                  horizon and the sky. Pitch and roll
  mode operating through the manual                                                     reference is similar to that of normal
  reaction jets.                                                                        aircraft. As with the periscope, drift
      More than one of these systems can                                                 (in this case, the drift of the stars as
  be used at a time. Since the automatic                                                well as of the terrain) may be used as
  reaction jets and the manual reaction                                                  a yaw reference. More precise head-
  jets are completely independent, it is                                                ing reference can be provided by sup-
  possible for the pilot to exercise con-                                                plying the Astronaut with the heading
  trol through the manual jets while the                                                 angles of the major stars which fall
  autopilot is exercising control through                                                within a tew degrees either side of
  the automatic jets. One occasion for                                                   the orbital plane. He can then orient
  use of both control systems would be                                                   the vehicle in yaw within a few de-
  in maneuvering in orbit when the As-                                                   grees whenever a known star appears
  tronaut desires to let the autopilot                                                   in the window.
  control two axes, such as roll and                                                        To train the Astronauts to use these
  pitch, while he takes control in yaw.                                                  Mercury control systems, a number of
  This manual control in a single axis                                                   fixed and moving base simulators have
  is possible through a set of valves                                                    been employed. No single trainer
  which cut off the automatic reaction                                                   could be provided that simulated all
  jets a single axis at a time, thus pro-     This fixed-base Procedures Trainer         of the control tasks, with all the avail-
   viding a number of possible combina-       allows the Astronaut to practice atti-      able control and reference systems, un-
   tions of automatic and manual con-         tude-control problems and emergency         der the required environmental condi-
  trol.                                       procedures for a Mercury flight. Con-      tions. The table on page 19 outlines
      In addition to the possibility of       trol problems and system errors can        the capability of each of the trainers
   combining manual and autopilot con-        be inserted into the trainer from the       we will describe here.
   trol, it is also possible to use the       instructor’s console in the foreground,       The Mercury Procedures Trainer,
   fly-by-wire with either the manual-        and the instructor can watch Astro-         shown at left here, incorporates a
   proportional or rate-command mode.         naut responses on the console’s panel.      complete simulation of the cockpit

 34 Astronautics / March 1962
                                                                                          training runs than will be typical of
                                                                                          the normal mission. (It is expected
                                                                                          that ultimately a criterion will be
                                                                                          reached such that less than 5% of the
                                                                                          trials at these high torque levels will
                                                                                          result in attitudes outside the permis-
                                                                                          sion limits.) This curve demonstrates
                                                                                          the difficulty of the task and the rela-
                                                                                          tively long periods of training that are
                                                                                          required to produce a high degree of
                                                                                          skill.
                                                                                               A second moving-base device used
                                                                                          in Astronaut training was the Multi-
                                                                                          Axes Test Facility (MASTIF), shown
                                                          25       x,     15      100
                                                                                          on page 38, a three-gimballed tum-
                                                                                          bling simulator at NASA Lewis Re-
                                             Left, the ALFA simulator without             search Center. Results of research
                                             the Astronaut aboard; and right, a           with this device were described by
                                             graph showing the percentage of trials       Useller and Algaranti at the 1960 IAF
                                             in which the Astronauts allowed the          meeting in Stockholm. In MASTIF,
                                             vehicle to get outside the retro-attitude    the Astronaut sits in the cockpit in the
                                             limits.                                      center of the gimballed device and is
                                                                                          rotated in each of three dimensions at
                                                                                          rates up to 30 rpm. Spinning each of
                                                                                          the gimbals at 30 rpm simultaneously
and support for the pressure suit. It        dom in roll and 35 deg of freedom in         produces a resultant random tumbling
permits simulation of both normal            pitch and yaw. The Astronaut opey-            rate on the cockpit of approximately
operation and malfunctions o the ma-
                                f            ates compressed air jets through a            50 rpm. After all three gimbals are
jor capsule systems, besides the at-         Mercury hand controller. Retrofire            moving at the desired rate, control can
titude-control problems, as we have          disturbance torques can be simulated          be turned over to the pilot, who at-
described them. The periscope dis-           through special compressed-air jets.          tempts with the use of reaction con-
play is simulated with CRT on which             Two attitude-control systems are           trols and the Mercury rate indicator
a large circle is generated to simulate      simulated on ALFA: Manual propor-             to bring the gondola to a stop. The
the earth for pitch and roll reference.      tional and fly-by-wire. In the fly-by-        graph on page 38 gives the time re-
Yaw reference is provided by a small         wire simulation, only the low-torque          quired by the Astronauts to stop the
circle which drifts across the display.      jets (used for attitude control in orbit      movement of ,the simulator as a func-
The external view through the window         when attempting to minimize fuel              tion of the resultant rotation rate of
is not animated.                             consumption) have been mounted on             the cockpit. As can be seen from
     The manual proportional mode has        ALFA. All three reference systems              this graph, the Astronauts were able
been emphasized in training the As-          are simulated. The periscope is sim-           to bring the trainer to a stop from a
tronauts, since it is independent of the     ulated through a bug-eye lens and a           50-rpm rotation in about 50 sec.
vehicle electrical systems and repre-        system of mirrors which present a                 The Astronauts performed this
sents the ultimate backup. Through           view of a circular screen on which a           maneuver with rate information only.
extensive practice with this system,         map of the earth is projected from a           The attitude indicators were not
 the Astronauts have achieved a high         film strip. The actual Mercury gyro            mounted on this trainer, since, if the
 level of skill in controlling the space-     package and instrument display are            vehicle were to tumble, the attitude
 craft.                                       mounted on the trainer. The window            indication would be unreliable. The
     During some of this training, the        display is simulated only schematically       pilot tended to fight the rotation in
 Astronauts have worn the Mercury             by an illuminated strip to represent          only one axis at a time throughout the
 full-pressure suit. With this suit in-       the horizon and small bulbs to simu-          time the simulator was in motion.
 flated to 5-lb over-pressure to simu-        late the stars.                               The lower line of the graph on page 38
 late a cabin decompression, they have                                                      gives the time during which the Astro-
 practiced controlling ,the spacecraft                                                      naut misapplied control thrust, adding
                                              Retrofire Training                            to the motion of the vehicle rather than
 attitude during simulated retrofire.
 Data from the Procedures Trainer in-            The graph above indicates early            reducing it. Note that this time of
 dicate that, while controlling in the        progress of training in the retrofire         thrust error tends to remain a constant
 pressurized suit is more fatiguing, the      problem using ALFA. It shows the              fraction of the total time to stop.
  Astronauts are able to keep the atti-       frequency with which the trainer was           There is little increase in the percent
  tudes within as close tolerances while      allowed to get outside, the attitude           of control errors with increasing rota-
  pressurized as under normal condi-          limits- 30 deg in yaw and roll and             tion rate within the rotational speeds
 tions.                                              in pitch -during retrofire, us-         used.
     In addition to this fixed-base Pro-      ing the periscope reference and the               This exercise on the MASTIF dem-
  cedures simulator, three moving-base        manual proportional control mode.              onstrated the ability of the Astronauts
  facilities have been utilized to train       Beyond these limits, retrpfire is inter-      to bring a tumbling vehicle to a sta-
  the Astronauts in attitude control.         rupted until the vehicle attitude is           tionary position in a relatively short
  The first of these is the Air-Lubricated    brought back within limits. This               period of time. It also demonstrated
  Free-Attitude      Trainer      (ALFA),     graph shows combined results for all           the adequacy of the rate indicator for
  shown on this page, which was de-            Astronauts through the first 100 trials.      this purpose. While tumbling is a
   signed and developed by Harold I.          The frequencies shown are not di-              very-low-probability event for the
  Johnson of the NASA Manned Space-            rectly applicable to the actual Mer-          Mercury capsule, it wcss felt that this
   craft Center. This trainer moves on         cury flights, since much higher mis-          training experience was highly desir-
   an air-bearing and has 360 deg of free-     alignment torques are used during              able as a general confidence builder.

 36 Astronautics / March 1962
                                                                                                               7


                                                                                                                           _o
                                                                                                               r

                                                                                                               +
                                                                                                               40
                                                                                                                           "-
                                                                                                                            50


                                                                                                               I   m   -

The photo at the left shows the MASTIF simulator at NASA Lewis Research Center, an Astronaut aboard trying his
hand at countering roll, pitch, and yaw with the side-arm controller. The graph shows stopping times and errors made
by Astronauts in training on MASTIF.



   Another moving-base simulator               The trends established indicate a
which has been used in the Mercury          decrease in performance due to ac-          Astrobee 1500
training program is the Navy's Johns-
ville centrifuge. This device simu-
                                            celeration and pressure-suit inflation.
                                            Preliminary analysis of the perform-        Up for Launch
lates linear acceleration loads associ-     ance data obtained during the retro-
ated with the mission. Two of the           fire task shows that, under accelera-
four types of control problems dis-         tion, error increased in both suit con-
cussed previously involve varying           ditions and is particularly marked in
levels of linear acceleration. Each         the hard-suit condition. No signifi-
retrorocket will produce approxi-           cant change in performance was
mately 0.4 g for the period it is firing.   noted during static runs between soft-
Thus, as much as 1.2 g may be pro-          and hard-suit conditions. In re-entry
duced by the retrorockets during the        rate damping tasks, once again error
short period that all three retro-          increased under dynamic conditions
rockets are firing simultaneously, The      and the effect of suit pressurization
Astronaut must also perform the re-         was greater under acceleration. These
entry rate-damping task under accel-        results tend to confirm the general
eration levels as high as 8 g during a      pattern observed for the retrofire con-
normal flight and higher in an abort.       ditions. An important consideration
    In the most recent Mercury training     in planning the Mercury training pro-
program, a simulated Mercury instru-        gram was the amount of centrifuge
ment panel and hand controller were         training required. These data seem
mounted in the Johnsville centrifuge        to demonstrate the desirability of
gondola. In addition, the gondola           training in a simulated acceleration
 could be depressurized to the 5-psi        environment and for making provi-
 level of the Mercury capsule in orbit.     sion for the use of the pressure suit
 At this ambient pressure level, it was     during such training.
 possible to operate with either a soft         Experience to date indicates that the
 or pressurized suit. Performance data       control systems are adequate to the        Last December, this Astrobee 1500 re-
 were collected both with the centri-        problems presented to the Astronaut        leased 'three sets of flares at an altitude
 fuge turning under dynamic (2.2 g           and that he is developing through the      of 1361 mi., midway between Cali-
 during retrofire or 11 g during re-         training program a high level of skill     fornia and the Hawaiian Islands, in an
 entry) and under static ( 1 g) condi-       in performing control tasks. It is         AFCRL experiment to position the
 tions to determine the effect of vary-      hoped that this brief review will          Islands geodetically. The two-stage
 ing acceleration levels on the Astro-       point out the extent to which the          vehicle, developed by Space-General
 naut's ability to control the vehicle.     Astronaut operates as an integral part      Corp., consists of tandem Astrobee 250
 For training purposes, the control          of the Mercury system and the oppor-        (first stage) and Almr solid rockets.
 tasks were made more difficult than         tunity the Mercury flight provides for     It can carry a 50-lb payload to an alti-
 the expected flight conditions,             demonstrating man's proficiency as a       tude of 2000 mi. or 200 Ib to an alti-
                                             controller for space vehicles.        ++   tude of 1100 mi.

3% Astronautics / March 1962