At SSECO,

the remaining

velocity we

for insertion
is displayed. to increase Insertion velocity

The c_--*_nd spacecraft

pilot will, velocity

after separation,

the prop,,l__ion system in the desired orbit.

as required

place approx_tel_ mately 25,770
580 miles down rathe at an inertial

of approxi-

feet per second.

Orbit Orbit vers, after

Phase phase is utilized experiments insertion for checkout and align,_.nt of systems, and re-entry. he performed orbital maneu-

and preparation

for retrograde

Tm,_diately the

a series
of system checks will systems. ground

to assure

capability ments

of guidance

Guidance tracking
computations informqtion.

and measureSystems com-

are checked

for accuracy

a_ainst
are updated pletion During tion

and aligned

by ground

command

(DCS) or by the pilot. and experiments

of system

checks,

the orbital

maneuvers
can be performed. in prepara-

the final orbit, and

guidance re-entry.

are re-aligned

Retrograde Retrograde puter
Phase phase begins approx_,_te_y five mlnutes before retrofire. The comcom-

is placed in re-entry

mode and begins System

collecting

data for re-entry

putations.

The Time Reference on spacecraft (depending

provides

indications and TR. a minus
at TR- 5 minutes At TR-? minutes or
(TR-276 seconds TR-256 seconds

7), TR-30

seconds, number)

on spacecraft

16 degree
bias is placed from orbit
on the pitch attitude attitude manually and maneuver during

needle.

The Propulsion control.

System Spacecraft

is switched attitude and attitude

to re-entry

is controlled are monitored

retrograde.

Retrograde

acceleration

by the IGS and velocity cha-ges are displayed for reference.

Re-Entr_

Phase The event timer counts
Re-entry phase begins _mmediately after retrofire.
through zero at retrograde and will be counting down from one hundred mlnutes (60 minutes on spacecraft 7) dlzringre-entry phase. After retrofire the retroShortly after retro-

all three packages.

In addition for use

to attitude

and acceleration

reference,

the I_J provides

AC and DC power

! [[_]" I I _

PROJ'-E-C"T

in other units of guidance and control.
The platform and electronics packages
are mounted on cold plates to prevent overheating.
References to x, y, and z attitude and translational axes pertain to inertial guidance only and should not be confused with structural coordinate axes.

Platform

The inertial platform (Figure 8-18) is a four gimbal assembly containing three miniature integrating gyros and three pendulous accelerometers. Gimbals allow
the gyro mounting frame (pitch block) to rP_n housing moves freely about them. housing, glmbal structure,
in a fixed attitude while the a
Major components of the platform are: gimbal angle syaehros,

torque motors,

resolvers, pitch,
gyros and accelerometers.
The gimbals from inside to outside are:
inner roll, yaw and outer roll. degrees of freedom. degrees. lock.
All gimbals, except inner roll, have 360
The inner roll gimbal is limited to plus and minus 15 of gimbal
Two roll gimbals are used to eliminate the possibility
Gimbal lock can occur on a three gimbal structure when an attitude of 0 At this timer he roll
degrees yaw, 0 degrees pitch, and 90 degrees roll exists.
and yaw gimbals are in the same plane and the yaw gimbal cannot move about its axis (gimbal lock). In the four gimbal platform, an angle of 90 degrees is
plATFORM gO-ORDINATES BODY CO-ORDINATES-XB, - xp, YP, Zp. YB, Zb.
"ICAL ACCEI.EROMETER (Z AXLS)
FIRST GI/_BAL (PITCH) _ FOURTH GIMBAL

ALONG 0(AXIS)

COURSE ACCELF_ROMIEEER_\.

A(_OSS (Y AXLS)

(INNER ROLL)

FM2-8-18

8-18 [ne_ia|

Gimba]

Structure
maintained between the inner roll and yaw gimbals thus preventing gimbal lock. The inertial components are mounted in the innermost g_mbal casting (pitch block) for rigidity and shielding from thermal effects. The gyros and asso-

are used either directly or through resolvers as the reference for gimbal control. Both phase and amplitude of signal generator outputs are functions Gimbal number one (pitch) is controlled directly by the Error signals produced bythe pitch gyro are amplified,
of gimbal attitude. pitch gyro output.
demodulated, and compensated, then used to drive the pitch gimbal torque motor. The first amplifier raises the signal to the level suitable for demodulation. After amplification, the signal is demodulated to remove the 7.2 KC carrier. A compensation section keeps the signal within the rate characteristics necessary

for loop stability.

When the signal is properly conditioned by the compenThe power amplifier supplies Torque motors then drive
sation section, it goes to a power amplifier.
the current required to drive gimbal torque motors. gimbals maintaining
gyro outputs at, or very near, _l].
Roll and yaw servo loops utilize resolvers to correlate gimbal angles with gyro outputs. Inner ro]] and yaw gimbals are controlled by a coordinate transWhen the spacecraft is at any
formation resolver mounted on the pitch gimbal.
pitch attitude other than 0 or 180 degrees, some roll motion is sensed by the yaw gyro and some yawmotion is sensed by the roll gyro. The amount of roll The
motion sensed by the yaw gyro is proportional to the pitch gimbal angle.
resolver, mounted on the pitch gimbal, coordinates roll and yaw gyro output with pitch gimbal angle. Resolver output is then conditioned in the same manner as
in the pitch servo loop to drive inner roll and yaw gimbals.

PROJEC

The outer roll gimbal is servo driven from the inner roll gimbal resolver. coordinate transformation resolver, mounted
on the inner roll gimbsl, monitors If the angle is anything other The error signal
the angle between inner roll and yaw gimb_1_.
than 90 degrees, an error signal is produced by the resolver.
is conditioned in the same manner as in the pitch servo loop to drive the outer roll gimbal. One additional circuit (phase sensitive electronics) is included The outer roll gimbal torque motor is mounted
in the outer roll servo loop.
on the platform housing and moves about the stable element with the spacecraft. As the spacecraft moves through 90 degrees in yaw, the direction that the outer roll gimbal torque motor must rotate, to compensate for spacecraft roll, reverses. Phase sensitive electronics and a resolver provide the phase reversal necessary for control. the yaw axis. The resolver is used to measure rotation of the yaw gimbal about As the gimbal rotates through 90 degrees in yaw, the resolver Resolver output is compared to a reference phase by the Nhen the resolver output changes phase, the

detects

the relay. with

of the relay switch.

turn off the computer When the low voltage
turns off the co_puter, sense.

it also breaks

to all ACPU circuits

low voltage it would

If power were not broken normal voltage
to the transient at the computer. capability
sense circuit, In atte,_ting be exceeded.

attempt

to __ntain voltage,

to maintain

normal

the auxiliary

Auxiliar_ Auxiliary nickle voltage
Power power consists battery of a battery and a trickle computer charger. during A 0.5 ampere-hour spacecraft for periods bus low of I00

cadmium

is used to supply w_ll

transients. or less.

The battery A trickle

supply

up to 9.8 amperes

mi11_seconds

charger

to maintain oscillator,

a f_11 charge transformer,

on the battery.

The charger

consists

of a transistor

8-68 CONFIDENTIAL

and rectifier.
The oscillator changes spacecraft bus voltage to AC.

The AC

voltage is then stepped up with a transformer and changed back to DC by a _11 wave diode rectifier. limiting Rectifier output is then applied, through a current The resistor limits charging current to
resistor, to the battery.
25mi1_amperes. source if desired.
Provision is included to charge the battery from an external

DIGITAL COMPUTER

SYST]_4DESCRIPTION
General The Digital Computer, hereinafter referred to as the computer, is a binary, fixed-point, stored-program, general-purpose computer, used to guide the spacecraft. inches deep. The computer is 18.90 inches high, 14.50 inches wide, and 22.75 It weighs 58.98 pounds. The major exter_1 External views of the computer are shown
on Figure 8-20. accompanying
characteristics are summarized in the

legend.

Using inputs from other spacecraft systems along with a stored program, the computer performs the computations necessary to develop the guidance and control outputs required by the spacecraft during the Pre-Launch and Re-Entry phases of the mission. In addition, the computer provides back-up guidance for the
launch vehicle during Ascent.
Inputs and Outputs The computer is interfaced with the Inertial Platform, Platform Electronics, Inertial Guidance System (IGS) Power Supply, Auxiliary Computer Power Unit (ACPU), Manual Data Insertion Unit (MDIU), Time Reference System (TRS), Digital Command System (DCS), Attitude Display, Attitude Control and Maneuver Electronics (ACME), Titan Autopilot, Pilots' Control and Display Panel (PCDP), Incremental Velocity Indicator (M), Instrumentation System (IS), and Aerospace Ground Equipment (AGE).

*Addresses

for CLD and PRO instructions

Data Word

_51 IM6.. _o I i_l _2 _31 1_4 _5 D
where each group of three bits is expressed as an octal character (from 0 to 7). An instruction word is thus expressed as a five-character octal number. The
operation code can take on values from O0 to 17, and the operand address can take on values from 000 to 777. Any operand address larger than 377 addresses address bit (A9)
the residual sector (sector 17) because the highest-order is also the residual identification bit.
A data word is expressed as a nineThe
character octal m,_mber,taking on values from 000000000 to 777777776. low-order character can take on only the values of O, 2, 4, and 6.

8-93 CONFIDENTIAL

Arithmetic Elements The computer has two arithmetic elements: and a multiply-dioxideelement. an add-subtract element (accumulator),
Each element operates independently of the other; Computer
however, both are serviced by the same program control circuits.
operation times can be conveniently defined as a number of cycles, where a cycle time represents the time required to perform an addition (140 usee). AI]
operations except MPY and DIV require one cycle; MPY requires three cycles, and DIV requires six cycles. Each cycle, the program control is capable of An MPY or a DIV
servicing one of the arithmetic elements with an instruction.
instruction essentially starts an operation in the multiply-divide element, and the program control m_st obtain the answer at the proper time since the multiplydivide element has no means of completing an operation by itself. _en an MPY
is co_,._nded,the product is obtainable from the multiply-dlvide element two cycle times later by an SPQ instruction. When a DIV is comm_nded, the quotient
is obtainable five cycle times later by an SPQ instruction.
It is possible to have one other instruction run concurrently between the MPY and the SPQ during multiply, end four other instructions run concurrently between the DIV and the SPQ during divide. However, an MPY or a DIV is always followed

the telescope. lens,

a germanium thermistor

meniscus

objective
a germanium-_mmersed direct

bolometer. reflected

The objective
lens is used to on the germanium

all the infrared

radiation,

by the mirrors, filter

_mmersion radiation microns
lens of the bolometer. of undesired frequencies.

The infrared The filter

is used to eliminate
has a band pass of 8 to 22 immersion lens focuses

(80,000

to 220,000

angstroms).

The germanium thermistor.

the infrared

radiation

on an immersed

The Horizon azimuth mirror.

Sensor field of vi_

is deflected

160 degrees

(+ 80) in the Positor is about
and 70 degrees The Positor
(12 up and 58 down) in azimuth

in elevation

by rotating

is rotated

by a drive yoke.

Rotation

an axis which of the Positor circuitry degrees

runs through mirror.

the center of the infrared

ray bundle

on the surface
The yoke is driven at a one cycle per second rate by package. pitch The center axis. of the az_,_th scan is 14 of

in the electronics

forward
of the spacecraft Elevation mirror
This is due to the mounting by the Posltor which

the scanner

heads.

deflection

tilts the Positor

to search

for or track the horizon.

8-1_6 CONFIDENTIAL

'::_'_ -

/ / / /

\ \\ \ \
",4"X _,,, @.,_=F-("""" \,_x\, ( ] i ,,. / j

-.-.,.',,,

.o.zoN

-.\_-.-_;/ ,

_ I AZIMLrfH AXIS OF ROTATION , ',t"_ (REF) RADIATION DRIVE YOKE
AXIS OF ROTATION POSITOR MIRROR i
INFRARED RADIATION (REF) t

,LOMETER

I I FIXED

THERMISTOR

GERMANIUM MENISCUS LENS

Infrared

Optics

CONFIDEENTIAL

rate at which the Positor tilts the mirror is a function of the mode of operation (track or search). In search mode,the Positor mirror moves at a two In track mode,the Positor mirror
cps search rate plus a 30 cps dither rate.
moves at a BO cps dither rate, plus, if there is any attitude error, a one or two cps track rate. spacecraft attitude The one or two cps track rate depends on the direction of error.

INFRARED

DETECTION
Infrared radiation is detected by the germanium-immersed thermistor bolometer. The bolometer contains two thermistors (temperature sensitive resistors) which are part of a bridge circuit. One of the thermistors (active) is exposed to The second thermistor (passive) is located

timer, a time correlation buffer, a mission elapsed time clock and a mechanical clock, Accutron panels. clock. The
digital clock, an event timer, an Accutron event timer, mission elapsed time digital clock are all mounted on the spacecraft
clock and mechanical The electronic timer

instrument

is located in the area behind the center instrument panel and the time correlation buffer is located in back of the pilot's seat.
The electronic timer provides
(I) an accurate countdown

of time-to-go to retro-

fire (TTG to T2) and tlme-to-go to equipment reset (TTG to TX) , (2) time correlation for the PCM data system (Instrumentation) and the bio-med tape recorders,
and (3) a record of elapsed time (ET) from llft-off.
The Time Correlation Buffer (TCB), used on spacecraft (S/C) 4 and 7, conditions certain output signals from the electronic timer, m_klng them compatible with blo-med and voice tape recorders. signals for Department of Defense Provision is included to supply buffered
(DOD) experiments if required.

The mission elated

time digital clock (on S/C 7) provides a digital indication The digital clock counts pulses from the elecstarted and stopped by operation of the elec-
of elapsed time from L_ft-off. tronic timer and is therefore tronic timer.

8-213 CONFIDENTIAL

The event timer provides the facilities for timing various short-term functions aboard the spacecraft. It is also started at lift-off to provide the pilots In case
with a visual display of ET during the ascent phase of the mission.
the electronic timer should fail, the event timer may serve as a back-up method of timing out TR.
The Aecutron clock (on S/C 4 and 7) provides an indication of Greenwich Mean Time (GMT) for the comm_nd pilot. The clock is powered by an internal battery
and is independent of external power or signals.
The mechanical calendar date.
clock provides the pilot with an indication of GMT and the In addition, it has a stopwatch capability. The stopwatch provides
an emergency method of performing
the functions of the event timer.
SYSTEM OPERATION Four components Accutron of the Time Reference System (electronic clock) function timer, event timer, of each other.

clock and mechanical

independently
The two remaining components (m_ssion elapsed time digital clock and time correlation buffer) are dependent on output signals from the electronic A functional diagram of the Time Reference timer.

an amount

as 1/8 second

and as large

Each data bit in a binary

data word represents

one individual

8-226 CONFIDENTIAL

PROJEC--'T'-'G

increment of time.

In looking at the flow diagram in Figure 8-67a the 24 secThe data bit
tions of the storage register represent its 24 individual cores.
which represents the smallest time increment (1/8 second) is stored in core number 24. It is referred to as the LSB in the data word. Core number 2B, then,
would store the next bit (representing 1/4 of a second) of the data word. The sequence continues, with core number 22 representing 1/2 second, back through. core number 1 with each successive core representing a time increment twice that of the preceding one. By adding together the increments of time repre-
sented by all of the cores, the total time capacity of the register can be determined. Thus, it is found that the ET and TR registers have capacities of Conversion
approximately 24 days and the Tx register, approximately two hours.
a data word to its representative time may be accomplished by totaling the
increments of time represented by the bit positions of the word where binary ones are present. For the data word shown in Figure 8-67b the representative

time is 583 3/8 seconds.

The process of shifting a data word into or out of a storage register is controlled by the occurrence of the shift and transfer pulses and by the condition of a control gate preceding each register and its _mite-in amplifier. The shift and
transfer pulses from the control section are supplied to a storage register whenever a data word is to be written in or read out. once each bit time for a duration of one word time. These _,1_es occur The actual flow of data
into a storage register is controlled by a logic gate preceding the write-in amplifier for each register. (Refer to Figure 8-68.) The count enable
input of the gate will have a continuously positive voltage applied after lift-off has occurred. The write-in pulse input will have a positive pulse applied for
(o) (DATA WORD FLOW-COUNTING PROCESS)

STORAGE REGISTER

"0"

"O"

"O" "O"
"1" "O"

out of a register, 1 vacant.

the remaining Before

core number

the next shift is

the bit which through

has been

out of the register and inserted

instantaneously, 1.

the arithmetic

cireuitry

back Thus, the first through

into core mlmber when

The process
is the same for each bit of the word. word is shifted 24. out of the register,
the last bit of the original
bit of the new one shifts the arithmetic operation. circuitry
into core number and enters
The last bit then cycles l, completing

the counting

8-230 CONFIDENTIAL
In the arithmetic time register registers

process,

the output from

of the elapsed

to an add circuit circuits.

and those

the TR and Tx are made up is quite

to separate

subtract

Both types

of circuits operation

of combinations s4m_lar,

of logic and switching being

circuits. logic

the main difference

in their

programs.
The add process bit position already
for the ET function of the word

consists coming

adding

a binary

"l" to the first If there is

(the LSB)

into the add circuit.
a "l" in that bit position, continues until
the "l" is carried the "l" reaches
to the next bit position.

The carry operation

an open bit position.
When the first bit of a data word s. the add circuit inverted register. core number produces
read out of the ET register output signal.

is a binary signal

"0",
a positive amplifier input

The positive

is then

by the write-in With

to the input a binary Thus,

of the storage into

a negative

to the register,

"l" is written
1 as the first bit of the new word. changed from a binary

the first

bit of the
word has been representative register
"0" to a binary bits

"l" adding

1/8 second to the back into the

time of the word.

The remaining

are written

just as they were

read out.

When word,
"l" is read out of the ET register of the add circuit

as the first Upon

bit of a data by the

will be negative.

inversion

write-in register

amplifier,

astable multivibrator, a power supply and logic circuitry. provides both input and output connections.
Operation The operation of the TCB is dependent on signals from the Instrumentation System and the electronic timer. In response to request pulses from the Instrumentation
System, the electronic timer provides elapsed time and time-to-go to retrograde words to both the instrumentation system and the TCB. supplied every 100 milliseconds. The elapsed time word is
In addition, once every 2.4 seconds it pro-
vides an extra elapsed time word and lOO mi]_iseconds later it provides a time to go to retrograde word.
The TCB requires retrograde word

elapsed

time information

only; therefore,

the time to go to response times,
is rejected. of recording
The tape recorders, time data time word

due to their

are not capable
every lO0 milliseconds is accepted
and for this The remaining by time
reason, only the extra elapsed 24 elapsed time words logic circuitry

by the TCB. word

and the time to go to retrograde Rejection of unused words

are rejected on their

in the TCB. words.

is based

relationship

to other

The TCB contains elapsed bits time word
three 8-bit magnetic is loaded once every

registers

the 24 bit extra out on in a

2.4 seconds.

The TCB then shifts rate is based clock pulse
at the rate of one every lOOmilllseconds. from the electronic timer.

The shift The first

data clock pulses word pulses causes
the TCB to shift out one bit of the data and the other

23 data clock

are disregarded.
Each bit that is shifted coded to make the bio-medical pulses
out of the shift register with tape recorder pulse

is stretched times.

in time and The output to
it compatible recorder "l."

response

is one positive The most

for a binary

"O" and two positive pulses

bit has two additional

to distinguish
it from the other 23 bits in the word. bit first and most
Data is shifted out of or marker bit
the TCB in a least significant last.
The output bio-medical _ quency pulse
to the voice tape recorders.

recorder

is the same basic it compatible

format with

as for the fre-

to make

the higher each output

response is chopped

characteristics

of the voice doubling

tape recorder,

into two pulses,

the frequency.

to reverse: number 1.

then number
The power the logic The driver
conversion section section

converts

the voltage-pulse to drive

to current provides

pulses

are used channels,

the servomotor. Each

four separate

one for each input.
channel has a logic gate and a power driver.
The logic gate permits the logic The gate senses
section output to be sensed at ten selected times each second.
only the occurrence of a positive signal which will allow the power driver to conduct and send a pulse of current through one of the four servomotor stator windings.
The sequence of pulses from the driver section causes the servomotor to step ten times each second and 45 each step. Figure 8-69 illustrates the step
positions relative to the sequence of operating pulses from the driver section. If pulses were applied to each of the four servomotor windings, without overlap, the unit would step 90o each repetition. It is this overlapping of signal
The display indicator is a rotating counter with wheels to display seconds, tens of seconds, minutes, and tens of minutes. It is coupled to the servomotor
through a gear train with a reduction ratio, from the servomotor, of 12.5;1. Therefore, as the servomotor rotates 450 (in one second), the indicator shaft turns 36 or i/i0 of a rotation. Since the seconds wheel is directly coupled
to the shaft and is calibrated from zero to nine, a new decimal is displayed each second. As the seconds wheel moves from nine to zero, the tens-of-seconds The operations of the other wheels are similar.
Updating The display.my be returned to zero or updated to some other readout with the The rotary switch
use of the DECR-INCR rotary switch on the face of the timer.
must be in the O position in order to have the timer operate at a normal rate;

8-25o CONFIDENTIAL

with the switch in one of the other positions,
it counts at a different rate.
the 0 position are utilized to make the timer count at 25 times its normal rate. The next closer positions are utilized to count at four times the The positions nearest the 0 position are used to count at a rate This position serves tom ore accurately place the

I NOTE

ORBIT ATTITUDE MANUEVERING SYSTEM JI
,NO._AT,VE@ F,T.0ow.I O" S._'_

,,D-,ACKAo,

"B" PAOI(AGE

@ _A_EF,I I

@ @ ROLL CLOCKWISE

_O_OU''0R_L_W'S I

(_) (_) TRA"_'.",E AE, I

OXIDIZER-TANK

WA,E_TA._ T_NS_,EOO_N I
"B" (REF) S/C 7 ONLY (S/C 7 ONLY)

FUEL TANK (S/C 7 ONLY)

CUTTER/ SEALERS WATER TANK

"A" (_:)

EgO.,,g_N,

RETRO SECTIOk

".

.-"

CAg_N SECTION __
Maneuvering 8-256 CONFIDENTIAL

Location

FMe2-_gS
The Gemini Spacecraft is provided with an attitude and maneuvering control capability. (Figure 8-72). This control capability is used during the entire
spacecraft mission, from the time of launch vehicle separation until the reentry phase is completed. Spacecraft control is accomplished by two rocket engine System (OAMS) and the Re-entry
systems, the Orbit Attitude and Maneuvering Control System (RCS).
The 0A_S controls the spacecraft attitude and provides maneuver capability from the time of launch vehicle separation until the initiation of the retrograde phase of the mission. The RCS provides attitude control for the re-entry module _ae OA_ and RCS respond to electri-
during the re-entry phase of the mission.
cal corm_andsfrom the Attitude Control Maneuvering Electronics (ACME) in the automatic mode or from the crew in the manual mode.

ORBIT ATTITUDE

AND MANEUVERING
SYST]_ DESCRIPTION The Orbit Attitude Maneuvering System (OAN_) (Figure 8-72) is a fixed thrust, cold gas pressurized, storable liquid, hypergolic bi-propellant, self contained propulsion system, which is capable of operating in the environment outside the earth's atmosphere. chamber assemblies Maneuvering capability is obtained by firing thrust The thrust chamber assemblies
(TCA) singly or in groups.
are mounted at vaious points about the adapter in locations consistent with the modes of rotational or translation acceleration required.

8-257 CONFIOENTIAL

CONI=ID_NTIAL

The O_

provides a means of rotating the spacecraft about its three attitude
control axes (roll, pitch, and yaw) and translation control in six directions (right, left, up, down, forward and aft). The combination of attitude and
translational maneuvering creates the capability of rendezvous and docking with another space vehicle in orbit. Spacecraft 3 does not have the capability to

Relief valves in the "B" package prevent over pressurization of the Burst diaphragms are provided in series
system downstream of the regulator.
with the relief valves, in the "B" package of S/C 4 and 7, to provide a positive leak tight seal between system pressure and the relief valve.
The "E" package provides a secondary mode of pressure regulation in the event of regulator failure. In the event of regulator over-pressure failure, resulting
in excess pressure passage through the regulator, a pressure switch ("E" package) intervenes and automatically is then controlled Control pressure closes the norms]ly open cartridge valve. the
Regulated pressure OAN_-PUISE package switch.
manually by the crew by utilizing information is obtained
from the "B" failure

regulated pressure

transducer.

Should regulator

under-pressure
occur, the crew can m_nually select the OA_3-REG switch to SQUIB.

8-_61 CONFIDENTIAL

opens the normally surant by-passes (OAMS-PULSE) "B" package

closed valve and closes

the normally Pressure

open valve,

thus presmanually the
the regt_lator completely. control
is then regulated obtained provides pressure
by the crew with regulated pressure

pressure

transducer. tanks.
The "B" package The regulated
a division is sensed indi-

of pressurant

flow to the propellant transducer downstream
by the pressure cating pressure

and provides

to the cabin

instrument,

of the regulator. to maintain

In the event

of regulator

failure,

the crew utilizes for proper prevent package

the reading

in the system check valves

in the propellant

tanks.

Three system.

back flow of prop_11Ant also affords

vapors

into the press_rant for prevention
The "B" on the downdia-

a safety feature

of over pressure
fuel and oxidizer stream phragm2

tank bladders.

Should
the system be over pressurized would first rupture the burst

of the reg_lator_

the over pressure
on S/C _ and 7_ then be vented will reset when

overboard

through returns
the relief valves. to normal.

The relief valves