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```									                   7. SPACECRAFT CONFIGURATION DESIGN

7.1 Passenger volume allowance on commercial aircraft
The pressurized cabin of a commercial airliner includes the flight deck in the nose cone,
the passenger cabin and cargo areas, and terminates at the aft pressure bulkhead. The
cross-sectional shape of the cabin is generally circular, or close to circular, because of the
structural and manufacturing benefits of such a shape. The passenger cabin comprises the
major portion of the volume and to simplify the analysis attention will be focused on it.
The fuselage width is set by the number of seats abreast, their width, and the width of any
aisles between the seats. Using data presented by Torenbeek (Ref. 1) the fuselage width
bf may be approximated by the following equation:

b f  c1  c2 aN a                                  (7-1)

Here we are using the notation of Torenbeek (Ref. 7-1) where a is the seat width and Na
is the number of seats abreast. Similarly, data for the length of the cabin Lc may be
correlated by

Lc  c3  pNr 
1.052
(7-2)

Here p is the pitch of the seat rows and Nr is the number of rows of seats while c3>1 is a
constant accounting for the presence of lavatories, galleys, etc. available for the
convenience of the passengers. Then the number of passengers that can be
accommodated is

N p  Na Nr                                    (7-3)

The approximation sign is used to note that we tacitly assume the number of seats abreast
to be a constant. On some aircraft there may be a few rows that have a different number
of seats abreast for various operational or design reasons. Now we may consider two
volume measures, the pressurized volume and the free volume. The pressurized volume is
defined as the gross volume contained within the pressure shell and for the passenger
cabin this is given by

             
Vpress        b2 Lc         c1  c2 aNa        c3  pN r 
2                1.052
f                                                       (7-4)
4             4

The free volume is defined as that volume readily accessible to the passengers in the
cabin neglecting the volume occupied by seats and partitions. Assuming the aircraft is
large enough for passengers to readily to move around one may define some average
headroom h, and then the free volume is given by

V free  b f Lc h   c1  c2 aNa  pNr 
1.052
c3 h      (7-5)

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If we use the approximation of Eq. (3) we may form the volume per passenger as follows:

0.052
V press          c2                       pN p 
 c3 p  1  2c2 a  c2 a 2 N a  
2
                               (7-6)
Np        4      Na                      N a 

In the same fashion we may determine the free volume per passenger to be

0.052
V free            c          pN p 
 c3 hp  1  c2 a                                           (7-7)
Np               Na        N a 

The last term on the right hand side of Eqs. (7-6) and (7-7) is a slowly varying function
that lies between about 1.1 and 1.3 for a wide range of typical airplanes, while the
remaining terms are all constants particular to a given aircraft. Reviewing the
characteristics of common commercial aircraft like Boeing’s 737, 767, and 777 families
and the regional turboprop ATR-72 we can tabulate some useful information as in Table
7-1.

Table 7-1 Average Fuselage Data for Commercial Aircraft

Na        c1         c2              c3            c3,pax         p (ft)           a (ft)     h (ft)   Nr
1         0.71       1.09            1.32          1.08           2.5              1.43       4        1-4
2         2.49       1.24            1.32          1.08           2.5              1.43       5        6-10
3         2.49       1.24            1.32          1.08           2.5              1.43       5.5      10-15
4         2.49       1.24            1.32          1.08           2.5              1.43       6        16-18
5         2.49       1.24            1.08          1.08           2.7              1.43       6        19-31
6         2.49       1.24            1.08          1.08           2.7              1.43       6        31-37
7         0          1.3             1.08          1.08           3                1.5        6        33-37
8         0          1.3             1.08          1.08           3                1.5        6        37-45
9         0          1.3             1.08          1.08           3                1.5        6        45
10        0                          1.08          1.08           3                1.5        6

For aircraft that seat four or more abreast Eq. (7-4) is satisfactory for determining the
pressurized volume because the fuselage cross section is generally circular. For smaller
aircraft, that is for Na<3, the pressurized volume is approximated by

V press  b f hLc , pax                                     (7-8)

Here Lc,pax is used to recognize that in the smaller diameter aircraft the cargo holds are in
the cabin forward and/or aft of the passenger compartment rather than below the floor so
the cabin as defined by Eq. (7-2) is longer than the passenger compartment. Thus, for
these smaller aircraft the cabin length Eq. (7-2) is used with c3 replaced by c3,pax. The
range of the number of rows Nr=Np/Na given in Table 1 is used to estimate the slowly
varying function (pNp/Na)0.052 that appears in Eqs. (7-6) and 7-(7). With all this
information we are now able to estimate the likely values of free and pressurized volume

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per passenger seat for commercial aircraft and these are shown as a function of Na in
Fig.7-1.

160
140       business jets        pressurized volume per seat
120
Volume (ft^3)

100
80
fighters
60
40
20                                        free volume per seat
0
0           2        4         6        8        10         12
Number of seats abreast

Figure 7-1 The variation of the nominal free and pressurized volume per
passenger for commercial aircraft is illustrated. Shown for comparison are typical
ranges for business jets and military fighter aircraft.

The interesting feature is that the free volume per passenger is essentially constant for all
commercial aircraft cases, with a range of from 35 to 50 ft3 per passenger. The
pressurized volume is about 20% greater than the free volume until the aircraft is large
enough that the (circular) cross-sectional area is sufficiently large to permit use of
pressurized above- and below-floor space for other uses besides passenger
accommodation. Thereafter, as would be expected, the pressurized grows linearly with
the cabin diameter.

Business jets may have twice the value of the specific volume as commercial airliners
since they typically are optimized for comfort. For example the Gulfstream G200, which
carries a maximum of 10 passengers, has a specific free volume of about 87 ft3/passenger
and a specific pressurized volume of about 109 ft3 per passenger. The larger G500, which
can carry 18 passengers, provides a specific free volume of 93 ft3 per passenger and a
specific pressurized volume of 125 ft3 per passenger. On the other hand, military fighter
aircraft have typical cockpit dimensions (Ref. 7-2) that suggest a specific free volume of
about 40 ft3/passenger, very much like that of commercial aircraft. The range of volume
for these types of aircraft is also indicated on Fig. 7-1 for comparison.

7.2 Application to crew volume in spacecraft cabins
One may draw the conclusion from the results of the previous section that when a
spacecraft cabin design is to accommodate relatively few people with relatively little
space for mobility while the being strongly constrained by weight and economic
considerations, the specific free volume should be in the range of 35 to 50 ft3 per person
with the pressurized volume being about 20% larger. Of course, using the aircraft

117
analogy tacitly assumes that the spacecraft mission duration is relatively brief, on the
order of a day. It seems likely that trained spacecraft crew members can be
accommodated by this level of free volume for somewhat longer periods, perhaps up to
several days. When the mission duration is longer and the crew members have duties that
require some sustained mobility it seems likely that a larger specific free volume be
available to them. The specific free volume in nuclear submarines, which have mission
durations measured in months, tends to be an order of magnitude greater, around 400 ft3
per person.

It doesn’t seem to follow that there should be a continuous functional relationship
between specific free volume and mission duration. Perhaps a quantum relationship may
be sufficient for estimating vehicle sizing requirements. An illustration of such a
relationship is shown in Fig. 7-2.

ISS
Mars
2500                                                        ?

1000

400
nuclear submarines
Vfree/Np (ft3)

100

40
Aircraft and orbital
spacecraft
10

1                 10   time (days)    100       1000

Figure 7-2 A notional quantum representation of specific free volume as a
function of mission duration

The nature of Fig. 7-2 also brings to mind whether or not it is reasonable to expect that
there is a continuum of mission durations. It is clear that orbital missions to and from the
ISS need only short times on the order of a day or so, while scientific work on the ISS
may require 100 days and a mission to Mars near to 1000 days. However, the 10 day
mission seems to be absent from this figure. Are there 10 day space missions under
consideration? If so, it seems likely that more specific free volume than for orbital
spacecraft would be necessary and perhaps something less than that required for nuclear
submarines would be advantageous. But is it really necessary to have a continuous

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function for Vfree/Np between 3 days and 30 days? A stepwise change in requirements, for
example, might be like that shown schematically in Fig. 7-3.

ISS
2500

1000

400
nuclear submarines
Vfree/Np (ft3)

100                    Intermediate missions

40
aircraft

10

1                   10   time (days)   100        1000

Figure 7-3 Specific free volume requirements as a stepwise function of mission
duration.

It seems likely that a “ten-day” spacecraft would not constitute a point design but would
need a broad margin of operational flexibility so that 5-day and 15-day missions could be
carried out with the same spacecraft. The quantum approach also arises naturally from
considering that the crew complement is figured in integer quantities. Does the increase
in specific free volume arising from a reduction in crew strength significantly improve
conditions for the conduct of the mission? Interestingly, the stepwise free volume
function in Fig. 7-3 may be thought of as moving through a space contained within some
pair of Celentano-like curves, which will be discussed in the next section.

7.3 Crew volume allowance
The number of crew members and mission duration are basic specifications that strongly
influence the vehicle configuration. The habitable volume required for each crew member
may be estimated by applying the Celentano volume criterion (ref. 7-3) which is an s-
shaped, “learning curve” shown in Fig. 7-4.

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1000                                                       free=40t0.58

free=20t0.58
Habitable                       Shuttle (8)
Volume
Shenzhou (3)
Kliper (6)
free 100                                                  Celentano volume
( ft3 per                    Orion (4)
Apollo (3)        criterion
person)
Gemini (2)

1
1                    10                  100      400    t (days)

Figure 7-4 Free volume per crew member as a function of mission duration.
The numbers next to the vehicle name denote number of crew members. The
Celentano criterion is also shown.

The Celentano criterion curve may be approximated in a piece-wise fashion according to
the following equations:

0<t<4 days: free=40 ft3/person (1.13 m3/person)
4<t<180 days: free=20t0.58 ft3/person                                             (7-9)
t>180 days: free=400 ft3/person (11.3 m3/person)

Figure 7-4 suggests that a doubling of the Celentano values is more representative of
current experience. The characteristics of the various vehicles shown are summarized in
Table 7-2. The International Space Station will have 15,000 cubic feet (425 m3) of
habitable volume but a crew complement of only 6, yielding 2500 ft3/person (70.8
m3/person), much more than even double the Celentano criterion. Note that 100 ft3
corresponds to a box roughly 4ft by 4 ft square and 6 ft high.

Table 7-2 Habitable volume characteristics of several space vehicles
Vehicle                                  Crew    Habitable volume (m3)
Apollo command module                    3       6.17
Kliper                                   6       20
Shenzhou                                 3       14
Space Shuttle                            8       71.5
Orion                                    4       11

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7.4 Vehicle mass characteristics
The overall mass and major dimensions of 10 manned space vehicles are presented in
Table 7-3 along with some other relevant data.

Table 7-3 Characteristics of 10 manned spacecraft

Name       Crew      length     max d      mass           mg/A     B        (l/d)^2/3
(m)        (m)        (kg)           (kPa)
Mercury 1             2.70       1.9        1300           4.50    2.812     1.264
Gemini 1              3.40       2.3        3200           7.56    4.723     1.298
Vostok 1              4.30       2.42       4258           9.08    5.677     1.467
Voshkod 2 or 3        5.00       2.42       4802           10.24   6.402     1.623
Apollo 3              3.20       3.9        5900           4.85    3.029     0.876
Soyuz       1 to 3    7.40       2.7        6251           10.71   6.695     1.959
Shenzhou 1 or more 8.65          2.8        7800           12.43   7.768     2.122
Shuttle 6 to 8        8.82       6.14       24251          8.04    5.023     1.273
Kliper      6         12.00      3.9        15000          12.32   7.700     2.116
CEV*        4 to 6    8.83       5          17170          8.58    5.363     1.461
* note: data estimated from current data

The mass of the space vehicle should scale with the two-thirds power of the volume since
spacecraft, like aircraft are essentially pressurized shell structures. Thus the mass should
be proportional to the shell area. Consideration of the published characteristics of 10
space vehicles results in the following correlation:

m  470  d 2 
2/3
(7-10)

The mass is given in kilograms and the overall length and maximum diameter in meters.
Comparison between this correlation and the actual data for the space vehicles is shown
in Fig 7-5 and 7-6. A further correlation was made between the number of crew
members and the reduced mass, m2/3, and this is shown in Fig 7-7. The correlation is
reasonable and the probable range for the mass of the proposed NASA Crew Exploration
Vehicle (CEV) is outlined on the figure.

121
9000
8000               470(ld^2)^.667
7000
6000

mass (kg)
5000
4000
3000
2000
1000
0
0     20         40            60       80
volume factor ld^2 (m^3)

Figure 7-5 Spacecraft mass as a function of the volume parameter. Note that
The scale for this graph is for relatively small volume factors

30000

25000

20000
mass (kg)

15000
470(ld^2)^.667
10000

5000

0
0   100        200           300       400
volume factor ld^2 (m^3)

Figure 7-6 Spacecraft mass as a function of the volume parameter. Note that
the scale for this graph is for relatively large volume factors

122
900
Kli
800                                                                   Shuttle
700

(mass)^2/3 (kg^2/3)
600       Mercury,
500       Gemini,
Vostok                                          CEV
400                                                       range
Voshkod
300                             Apollo
200                             Soyuz
Shenzhou
100
0
0              2              4                 6           8             10
number of crew members

Figure 7-7 Correlation between the number of crew members and the reduced
mass of a space vehicle

7.3 Ballistic coefficient
Also shown in Table 7-3 is the ballistic coefficient for each of the vehicles calculated on
the basis of the given mass and dimensions and an assumption of an average C D0=1.6
estimated from Fig. 5-5 for typical afterbody cone angles. Then using the analysis of
Section 3-2 which gave an estimate of the ballistic coefficient as

2/3
5.87  l 
B                                                  (7-11)
CD  d 

The calculated value for the ballistic coefficient is shown as a function of (l/d)2/3 in Fig.
7-8. The data indicate that Eq. 7-11 is reasonably correct since the data is fit well by the
linear function

2/3
l
B  3.6                                            (7-12)
d 

The coefficient is very close to 5.87/CD, for CD close to the estimated value of 1.6.The
only vehicle that deviates substantially from this correlation is the Apollo spacecraft. This
discrepancy may be due to the fact that the length in the Apollo vehicle may be
overstated since the afterbody is extended to almost a complete cone whereas most other
capsule-like spacecraft have a truncated conical afterbody. On the other hand the space
shuttle, which is more like a space plane does fit the correlation given.

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9.000

Ballistic coefficient B (kPa)
8.000
7.000
6.000       B=3.6(l/d)^0.667
5.000
4.000
3.000
2.000
1.000
0.000
0.000       0.500          1.000       1.500   2.000   2.500
(l/d)^0.667

Figure 7-8 Correlation between the ballistic coefficient for 10 spacecraft and the
fineness ratio l/d of the vehicle, l/d

7.4 Spacecraft configurations
The most celebrated spacecraft capsule is probably the Apollo capsule. A detailed
drawing of the capsule is shown in Fig. 7-5

Figure 7-5 The Apollo space capsule

The other most recognized spacecraft is the Space Shuttle Orbiter which is shown in Fig.
7-6. Other vehicles may be found in Refs. 7-4, 7-5, and 7-6.

124
Figure 7-6 The Space Shuttle Orbiter (Ref. 7-5)

7.5 Spacecraft systems
Supporting manned systems in space requires an elaborate array of environmental control
and life support systems. Design aspects of the variety of functions and systems used on
previous manned missions, both by the United States and by Russia/U.S.S.R. may be
found in Refs. 7-6 and 7-7. The various spacecraft systems and a description of their
function is given in Tables 7-4 and 7-5.

Table 7-4 Crew and Life Support Systems

System                           Description

Control-communications           Communication with ISS and ground
Crew systems-seats               Ergonomic restraint system
Crew systems-escape              Safe abort system
EC/LS-HVAC                       Heating, ventilating, and air conditioning
EC/LS-water                      Potable water for crew
EC/LS-waste                      Air purification and personal waste handling
EC/LS-fire control               Fire suppression system
EC/LS-emergency systems          Food, medical, and auxiliary power supplies
Landing systems-parachutes       Stowage and release capability

125
Table 7-5 Structure, Propulsion, Power and Control Systems

System                             Description

Structure-TPS                      Protect vehicle from reentry heating
Propulsion-OMS                     Orbital insertion and attitude control on station
Propulsion-retro                   De-orbit
Propulsion-tanks                   Contain fuel for all propulsion and power
Power-generation                   Fuel or solar cells
Power-distribution                 Wiring harnesses
Power-storage                      Batteries
Control-GNC                        Guidance, navigation, and control system
Control-data mgmt                  Systems monitoring and control

The maintenance of a suitable atmosphere depends on the objectives shown in Table 7-6.
Lithium hydroxide scrubbers follow the chemistry process give below

LiOH + CO2 → LiHCO3
2 LiHCO3 + CO2 → Li2(CO3) + H2O

Table 7-6 Spacecraft Atmosphere Revitalization

Atmosphere Mercury            Skylab           Orbiter          Spacelab      International
revitalization Gemini                                                         Space Station
Apollo
CO2 removal LiOH              Regenerable      Similar to       Similar to    Similar to
canisters      molecular        Mercury, et al   Mercury,      Skylab. CO2
sieve with                        et al         vacuum
Zeolite 5A                                      desorbed to
space
O2              None          None             None             None          Solid polymer
generation                                                                    electrolyte
device
Trace           Activated     Activated        Activated        Similar to    Activated
contaminant     charcoal in   charcoal in      charcoal, CO     Orbiter       charcoal with
control         LiOH          molecular        to CO2 by                      a high
canisters     sieve, filters   catalysis,                     temperature
for              NH3 absorbed                   catalytic
particulates     by HX                          oxidizer,
condensate,                    filters for
filters for                    particulates
particulates

126
Table 7-7 Spacecraft Atmosphere Control and Supply

Mercury          Skylab          Orbiter        Spacelab       International
Gemini                                                         Space
Apollo                                                         Station
Atmosphere 100% O2 at        72-28 O2-N2     22-78 O2-N2    Same as        Same as
composition 34.5kPa (60-     at 34.5kPa      at 101kPa      Orbiter        Orbiter
40 O2-N2 at
launch for
Apollo)
Atmospheric CO sensor        CO and          none           none           N2, O2, H2,
monitoring  (Mercury         trace                                         CH4, H2O,
only)            contaminant                                   and CO2
sensors                                       monitors in
lab module
Gas storage   O2 as          O2 and N2       Same as        N2 as          O2 as
52MPa gas      as 21MPa        Skylab,        21MPa gas,     16.5MPa gas
in Mercury,    gases           metabolic O2   O2 from        and N2 as
O2 as 6MPa                     from           Orbiter        21MPa gas
cryogenic                      cryogenic      supply at
liquid in                      source for     690kPa
Gemini and                     power
Apollo                         system
Temperature   Mercury        Skylab          Orbiter        Spacelab       International
and           Gemini                                                       Space
humidity      Apollo                                                       Station
control
Atmosphere    Condensing     CHX with        Centralized    Like Orbiter   Like Orbiter,
temperature   heat exchan-   Coolanol 15     water/air                     condensate
and           gers (CHX)     coolant.        CHX. Air                      stored in
humidity      for suit and   Combination     bypass ratio                  tanks
control       cabin. Pilot   of air duct     for T
regulates T    and wall        control,
by water       heaters for T   condensate
flow rate,     control         removed by
condensate                     wiper and
removed by                     centrifugal
sponge                         separator
system or
wicks
Cabin         Cabin fans     Ventilation     Cabin fan      Cabin fan      Like Orbiter
ventilation                  ducts with      with
fans and        ventilation
portable fans   ducts

127
Table 7-8 Spacecraft Atmosphere Temperature and Humidity Control

Mercury         Skylab          Orbiter         Spacelab        International
Gemini                                                          Space
Apollo                                                          Station
Atmosphere    Condensing      CHX with        Centralized     Like Orbiter    Like Orbiter,
temperature   heat exchan-    Coolanol 15     water/air                       condensate
and           gers (CHX)      coolant.        CHX. Air                        stored in
humidity      for suit and    Combination     bypass ratio                    tanks
control       cabin. Pilot    of air duct     for T
regulates T     and wall        control,
by water        heaters for T   condensate
flow rate,      control         removed by
condensate                      wiper and
removed by                      centrifugal
sponge                          separator
system or
wicks

Table 7-8 Spacecraft Thermal Management

Mercury         Skylab          Orbiter         Spacelab        International
Gemini                                                          Space
Apollo                                                          Station
Thermal       Condensate      Space           Freon           Water loop      Circulating
control and   boiler on       radiators       coolant loop    interfaced      water over
heat          Mercury,                        to radiators,   with Orbiter    cold plates
rejection     space                           ammonia         Freon loop      and HXs,
Gemini,                         flash                           space
Apollo
Equipment     Cold plates     Like            Like            Like            Like Orbiter
cooling       and cabin air   Mercury         Mercury         Mercury
cooling by                      plus            plus
passing                         dedicated       dedicated
through                         liquid/air      liquid/liquid
CHX                             HXs and         HXs and
systems         change
thermal
capacitors

128
Table 7-9 Spacecraft Water Recovery and Management

Mercury      Skylab       Orbiter      Spacelab            International
Gemini                                                     Space Station
Apollo
Water         Potable only Potable only Potable only Not                 Potable only
supply                                               applicable
quality
Water         None           Iodine         None          Not            On-line
monitoring                   sampler                      applicable     conductivity
and oof-line
microbial
count
Water         None, vent     Store waste    Like Skylab   Not            Urine: vapor
processing    waste water,   water until                  applicable     compression
or store and   tanks full,                                 distillation.
send excess    then vent                                   Potable and
to CHX                                                     hygiene:
(Apollo)                                                   multifiltration,
ion-exchange,
and catalytic
oxidation

Table 7-10 Spacecraft Fire Detection and Suppression

Fire          Mercury        Skylab         Orbiter       Spacelab       International
Detection     Gemini                                                     Space Station
and           Apollo
Suppression
Suppressant   Water from     Portable       3 remote      Like Orbiter   CO2
food           acqueous gel   and 3                        extinguishers,
rehydrator.    (foam)         portable                     Cabin
Manual         extinguisher   Halon 1301                   depressuri-
depressur-                    bottles.                     zation
ization.                      Cabin
Acqueous                      ization
gel extin-
guisher
Detection     Crew senses    UV             Ionization    Like Orbiter   Photoelectric
detectors      smoke                        smoke
detectors                    sensors

129
7.5 References
7-1 Torenbeek, E.: Synthesis of Subsonic Airplane Design, Kluwer Publishing, 1986

7-2 Raymer, D.P.: Aircraft Design – A Conceptual Approach, AIAA, Reston, VA, 1989

7-3 Woodcock, G.R.: Space Stations and Platforms, Orbit Book Company, Malabar, FL,
1986.

7-4 www.spacex.com/photo_gallery.php

7-5 www.kistleraerospace.com/photogallery/main.html

7-6 www.nasa.gov/mission_pages/constellation/orion/index.html

7-7
http://spaceflight1.nasa.gov/history/shuttle-mir/multimedia/diagrams/shuttle/diagram-
shuttle.htm

7-8 Wieland P.O.: “Designing for Human Presence in Space: An Introduction to
Environmental Control and Life Support Systems (ECLSS), NASA Reference
Publication 1324, 1994
http://ntrs.nasa.gov/search.jsp?R=373449&id=5&qs=Ntt%3Ddesigning%252Bfor%252B
human%252Bpresence%252Bin%252Bspace%26Ntk%3Dall%26Ntx%3Dmode%2520m
atchall%26N%3D0%26Ns%3DHarvestDate%257c1

7-9 Wieland, P.O.: “Designing for Human Presence in Space: An Introduction to
Environmental Control and Life Support Systems (ECLSS), Appendix I, Update –
Historical ECLSS for U.S. and U.S.S.R./Russian Space Habitats”, NASA/TM – 2005 –
214007, July, 2005
http://ntrs.nasa.gov/search.jsp?R=46169&id=2&qs=Ntt%3Ddesigning%252Bfor%252Bh
uman%252Bpresence%252Bin%252Bspace%26Ntk%3Dall%26Ntx%3Dmode%2520ma
tchall%26N%3D0%26Ns%3DHarvestDate%257c1

130

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