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Space Shuttle Avionics
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 1 of 18
---------------------------------------------------------------------------
AVIONICS SYSTEMS
The Space Shuttle avionics system controls, or assists in controlling,
most of the Shuttle systems. Its functions include automatic determination
of the vehicle status and operational readiness, implementation sequencing
and control for the external tank and solid rocket boosters during launch
and ascent, performance monitoring, digital data processing, communica-
tions and tracking, payload and system management, and guidance, naviga-
tion, and control, as well as electrical power distribution for the orbit-
er, external tank, and solid rocket boosters.
Automatic vehicle flight control can be used for every phase of the
mission except docking, which is a manual operation by the flight crew.
Manual control - referred to as the control stick steering (CSS) mode -
also is available at all times at the flight crew option.
The avionics equipment is arranged to facilitate checkout, access, and
replacement with minimal disturbance to the other subsystems. Almost all
electrical and electronics equipment is installed in three areas of the or-
biter: the flight deck, the forward avionics equipment bays in the mid
deck of the orbiter crew compartment, and the aft avionics equipment bays
in the orbiter aft fuselage. The flight deck of the orbiter crew compart-
ment is the center of avionics activity, both in flight and on the ground,
except during hazardous servicing operations before flight. Before launch,
the orbiter avionics system is linked to ground support equipment through
umbilical connections.
The Space Shuttle avionics system consists of more than 300 major elec-
tronic "black boxes" located throughout the vehicle, connected by more
than 300 miles of electrical wiring. The black boxes are connected to a
set of five computers through common party lines, called data buses. The
black boxes offer dual or triple redundancy for every function.
The avionics are designed to withstand multiple failures through redun-
dant hardware and software (computer programs) managed by the complex of
five computers; this is called a fail-operational/fail-safe capability.
Fail-operational/fail-safe capability is provided by a combination of hard-
ware and software redundancy. Fail-operational performance means that af-
ter a first failure of a system, redundancy management allows the vehicle
to continue on its mission. Fail-safe means after a second failure, the
vehicle still is capable of returning to a landing site safely.
The status of the individual avionics components is checked by a sys-
tems monitoring computer program. The status of critical vehicle functions
such as the payload door position, external tank and solid rocket booster
separation mechanisms, and excessive temperatures for certain area are mon-
itored continuously and displayed to the crew.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 2 of 18
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DATA PROCESSING SYSTEM
The orbiter relies on computerized control and monitoring for success-
ful performance. The data processing system (DPS) through the use of var-
ious hardware components and its self-contained computer programming (soft-
ware) provides this monitoring and control.
The data processing system consists of five general-purpose computers
for computation and control; two magnetic-tape mass memories for large-vol-
ume bulk storage; time-shared, serial digital data buses (essentially par-
ty lines) to accommodate the data traffic between the computers and other
orbiter systems; 19 multiplexer/demultiplexer units to convert and format
data at various systems; three engine interface units to command the orbit-
er main engines; and four multifunction television (cathode ray tube -
CRT) display systems so the crew can monitor and control the vehicle and
payload systems.
The software stored in and executed by the orbiter computers is the
most sophisticated and complex set of programs ever developed for aero-
space use. The programs are written to accommodate almost every aspect of
the Space Shuttle operations including vehicle checkout at the Rockwell
Palmdale (CA) assembly facility, prelaunch and final countdown, turnaround
activity at the Kennedy Space Center, and control during ascent, on-orbit,
entry, and landing and abort or other contingency mission phases.
In-flight programs monitor the status of vehicle systems; provide con-
sumable computations; control the opening and closing of the payload bay
doors; operate the remote manipulator system; perform fault detection and
annunciation, provide for payload monitoring, commanding, control, and da-
ta acquisition; provide antenna pointing for the various communications
systems; and provide primary and backup guidance, navigation, and control
for ascent, on-orbit, entry, landing, and abort.
These computer programs are written so they can be executed by a sin-
gle computer or by all computers executing and identical program in the
same time frame. The multicomputer mode is used for critical phases such
as launch, ascent, entry, and abort.
The orbiter software for a major mission phase must fit into the 106,
496-word central memory of each computer. Each computer consists of a cen-
tral processor unit (CPU) and an input/output processor (IOP). The CPU per-
forms the arithmetic and logical processing of data, provides control and
handling of interrupts and program control of its corresponding IOP, and
manages redundant systems such as sensors. The memory capacity of each com-
puter CPU is 81,920 words. All data transmissions between the computers
and vehicle systems are performed by the IOP under control of the CPU. The
IOP receives data from the CPU, formats it, and relays commands to vehicle
systems. The IOP also receives data from the vehicle systems and formats
it for the CPU. The memory capacity of each computer IOP is 24,576 words.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 3 of 18
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To accomplish all of the computing functions for all mission phases,
approximately 400,000 words of computer memory are required. To fit the
software needed into the computer memory space available, computer pro-
grams have been subdivided into nine memory groups corresponding to func-
tions executed during specific flight and checkout phases. As an example,
one memory group accommodates final countdown, ascent, and aborts; another
on-orbit operations; and another the entry and landing computations. Dif-
ferent memory groups support checkout and ground turnaround operations and
system management functions. Thus, in addition to central memory stored in
the computers themselves, 34,000,000 bytes of information can be stored in
two mass memories.
The orbiter computers are loaded with different memory groups from mag-
netic tapes containing the desired program. In this way all the software
needed can be stored in mass memory units (magnetic tape machine) and load-
ed into the computers only when actually needed. Critical programs and da-
ta are loaded in both mass memories and protected from erasure. Normally
one mass memory is activated for use and the other is held in reserve. How-
ever, it is possible to use both simultaneously on separate data buses or
communicating with separate computers. The data stored in the mass mem-
ories include prelaunch and preflight test routines, fault isolation diag-
nostic test programs, cathode ray tube (CRT) display formats, overlay pro-
gram segments to be loaded during specific mission phases, and duplicate
copies of resident on-line programs for initial loading, reloading, or re-
configuration of the computers. The mass memories are an advanced form of
data storage and fill the gap between slow access drives of high storage
capacity and discs or drums with fast access but relatively low storage
capacity. In contrast to disc or drum memories, the mass memories consume
power only when active.
The DPS software is divided into two major groups, called system soft-
ware group and applications processing software.
At the top is the system software group, which consists of three sets
of programs: the flight computer operating program (the executive), which
controls the processors, monitors key system parameters, allocates comput-
er resources, provides for orderly program interrupts for higher priority
activities and updates computer memory; the user interface programs, which
provide instructions for processing crew commands or requests; and the sys-
tem control program, which initializes each computer and arranges for the
multicomputer operation during flight-critical periods. The system soft-
ware group tells the computers how to perform and how to communicate with
other equipment.
The second level of memory groups is the applications processing soft-
ware. This group contains (1) specific software programs for guidance, nav-
igation, and control which are required for launch, ascent flight to or-
bit, maneuvering on orbit, entry, and landing on a runway; (2) systems man-
agement programs which contain instruction for loading memories in the
main engine computers and for checking the instrumentation system in addi-
tion to aiding in vehicle subsystem checkout and in ascertaining that crew
displays and controls perform properly and update the inertial measuring
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 4 of 18
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unit state vectors; (3) payload processing programs which contain instruc-
tions for control and monitoring of orbiter payload systems which can be
revised depending on the nature of the payload; and (4) vehicle checkout
programs which are required to handle data management, performance monitor-
ing, and special processing and display and control processing.
The two software program groups are combined to form a memory config-
uration for a specific mission phase. The software programs are written
in HAL/S (high-order assembly language / Shuttle) especially developed for
use in real-time space applications. These programs are grouped by func-
tion and partitioned into memory configurations. When requested, memory is
reconfigured from mass memory so operating sequences for the needed func-
tion can be overlaid into the main computer memory.
The highest level of the applications software is the OPS (operational
sequences) which are required to perform part of a mission phase. Each OPS
is a set of unique software required to perform phase-oriented tasks. An
OPS can be further subdivided into groups called major modes, each repre-
senting a portion of the OPS mission phase. As an example, the launch
phase (OPS-1) is subdivided into six major modes.
Each major mode has with it an associated CRT display which provides
the flight crew with information concerning the current portion of the mis-
sion phase. The display function of OPS software presents a fixed format
of data and configuration status on a CRT, which is not subject to flight
crew manipulation and is used only to provide the flight crew with informa-
tion.
The specialist (SPEC) function of the OPS software is a block of soft-
ware associated with one or more OPS which has an associated CRT display
and enables the flight crew to monitor and manipulate the vehicle systems
via keyboard entries.
The multifunction CRT display system provides the flight crew with the
ability to interface with and control the onboard software, observe vehi-
cle system data, and monitor error or fault messages. The system is compos-
ed of three components: display electronics units (DEU), keyboard units
(KBU), and display units (DU), which include the CRT's.
The flight crew has two keyboards, on the left and right sides of the
flight deck display and control center console. There are three DU-CRT's
on the flight deck forward display and control console. Each CRT is 127 x
177 millimeters (5 x 7 inches). There is also one keyboard and one DU-CRT
at the aft side station flight deck display and control console. The three
DU-CRT's at the forward console are connected to each of the forward cen-
ter console keyboards. The DU-CRT at the aft station is connected to the
keyboard at that station.
The DU uses a magnetic-deflected electrostatic-focused CRT. When sup-
plied with deflection signals and video input, the CRT will display alpha-
numeric and graphic information. Characters can be flashed and the CRT
brightness varied for individual characters. The CRT has a single-color
(green) phosphor.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 5 of 18
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The four DEU's provide storage of display data, the computer/keyboard
unit and computer/display unit interface display generation, updating, and
refreshing, keyboard entry error checking, and keyboard entry echoing to
the DU's
The three keyboard units provide the crew wit ha controlling interface
for software operations and management. Each keyboard has 32 momentary-
contact (pushbutton) function and numeric keys. Using these keys, the
flight crew can ask the computer more than 1,000 questions about the
flight and conditions of the vehicle. The DU's provide the flight crew
almost immediate response to the inquiries through display graphs, traject-
ory plots, and prediction about flight progress. The flight crew controls
the Space Shuttle system operation through the use of the keyboards. In
conjunction with the DU's, the flight crew can alter the system configura-
tion, change data or instructions in the computer main memory, change mem-
ory configurations corresponding to different mission phases, respond to
error messages and alarms, request special programs to perform specific
tasks, run through operational sequences for each mission phase, and re-
quest specific displays.
The input-output processor (IOP) of each computer has 24 independent
processors, each of which controls one of the 24 data buses used to trans-
mit digital data between the computers and vehicle systems, and secondary
channels between the telemetry system and units that collect instrumenta-
tion data. The data transfer technique uses time-division data multiplex-
ing with pulse code modulation. In this system, data channels are multi-
plexed together, one after the other, and information is coded on any giv-
en channel by a series of binary pulses corresponding to discrete informa-
tion. The information transmission word length is 28 bits. The first three
bits provide synchronization and indicate whether the information is com-
mands or data. The next five bits identify the destination or source of
the information. For command words, 19 bits identify the data transfer or
operations to be performed; for data words, 16 of these 19 bits contain
the data and 3 bits define the word validity. The last bit of each word
format is for an odd parity error test. The 24 data buses are connected
to each IOP via multiplexer interface adapters (MIA's) which receive, con-
vert, and validate the serial data in response to discrete signals calling
for available data to be transmitted or received. The data buses are organ-
ized into seven groups: intercomputer communication, display keyboard,
flight critical, mass memory, payload launch/boost, and instrumentation.
Interface adaptation between the data bus network and most vehicle sys-
tems is accomplished by multiplexer/demultiplexers (MDM). The MDM's are
used in numerous remote locations in the vehicle to handle the functions
of serial data time multiplexing/demultiplexing associated with the digit-
al data buses and for signal conditioning. The MDM's act as translators
and put information on or take it off the data buses. For the development
flight tests, there are 27 MDM's on the orbiter and two on each SRB for a
total of 31. In the operational configuration, there will be 23 MDM's,
thus subtracting the eight MDM's that make up part of the DFI.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 6 of 18
---------------------------------------------------------------------------
The MDM's receive from the vehicle systems hundreds of analog signals
which can be minus 5 to plus 5 Vdc, 28 Vdc discrete signals, and serial or
digital words, and converts these into a digital-serial output (which is a
digitized representation of the signals and data). The digital-serial out-
puts are transmitted via the data buses to the computers and to the pulse
code modulation (PCM) master unit.
The technique of transferring serial-digital computer data via the da-
ta buses to the MDM's and then to vehicle systems is called multiplexing.
Each computer sends serial-digital downlist data through four instru-
mentation buses to the pulse code modulation master unit, where it is mix-
ed with instrumentation and payload data and transmitted to ground down-
link telemetry.
The PCM also formats the vehicles operational instrumentation and sel-
ected development flight instrumentation into serial digital for transmit-
tal to telemetry.
The four instrumentation buses also transmit non-flight-critical orbit-
er system data from the PCM master unit to each computer for display on
the flight crew CRT's The PCM master unit contains a programmable read-
only memory (PROM) for accessing subsystem data, a random-access memory
(RAM) in which to store system data, and a memory in which data from the
computers are stored for incorporation in the downlink telemetry.
The MDM's controlled by either the computers or pulse code modulation
master unit are a demand response system via the data buses. A command
from either can order the applicable MDM to collect data and transmit the
data back to the controlling hardware.
Uplink software provides for the ground to send commands and data to
the orbiter via the S-Band transponder communications link. The orbiter
uplink software interfaces with network signal processors to the computers
via one of the flight-critical MDM's.
All data is time-tagged by three master timing units (MTU), which pro-
vide a Greenwich Mean Time (GMT) base as well as mission elapsed time and
event time. The system software in each computer selects the GMT from one
of the MTU's or from the computers own internal clock with frequent up-
dates from the MTU's as a function of timekeeping redundancy management.
The timekeeping software can be controlled by the flight crew via manipula-
tion of the specialist function CRT display. The MTU's also supply syn-
chronizing signals to other electronic circuits.
All computer communications with the DU-CRT display system are trans-
mitted and received over the display keyboard buses.
The guidance, navigation, and control system is composed of four orbit-
er computers and other major components which make up the primary flight
control system. The computers use a program called the digital autopilot
to control the vehicle through launch, ascent, on-orbit, deorbit, entry,
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 7 of 18
---------------------------------------------------------------------------
and landing. The guidance, navigation, and control system provides auto-
matic or manual (control stick steering) control of the vehicle in all
flight phases. During launch most of the computer commands are directed
to gimbal the main engines and solid rocket boosters. To circularize the
orbit, in orbit, and for deorbit, the computer directs the orbital maneuv-
ering system. At external tank separation, in orbit, and during a portion
of entry, vehicle attitude control commands are directed to the reaction
control system. In atmospheric flight the computers direct the orbiter
aerodynamic flight control surfaces.
During critical mission phases (launch and entry), four of the comput-
ers are assigned to perform GN&C tasks, operating as a cooperative redun-
dant set. One computer acts as a commander of a given data bus in the
flight control scheme and initiates all bus transactions. The noncommand-
er computers on the same bus listen to all incoming data that the command-
er requests. Thus, each response to a request by any computer is heard by
all performing the same redundant operations and verified for consistently
identical output. The computer redundancy management software module cen-
ters around the concept that each computer compares its outputs with the
other computers in the set. If the comparison disagrees, the disagreement
is displayed to the flight crew as a CRT message; however, processing con-
tinues.
Each of the computers operating in a redundant set operates in synchro-
nized steps and cross-checks results of processing about 440 times per sec-
ond. If a computer operating in a redundant set fails to meet the synchro-
nization requirements for redundant set operations, it would be removed
from the set. Each computer performs about 325,000 operations per second
during critical phases of the mission.
As an example, Computers 1 through 4 are operating in a redundant set
when Computer 1 fails to stay synchronized with the other three. Computer
1 software recognizes the disagreement and also recognizes that it has
been voted failed by the other three computers. Computer 1, therefore sets
a self-fail vote and does not vote the other three computers failed.
All intercomputer communications other than synchronization are trans-
mitted and received over four specific buses. Cross-strapping of the four
buses to the four computers allows each computer access to the status of
the data received or transmitted by the other computers, making possible
the verification of identical results among the four computers. The four
computers are loaded with the same software programs. Each bus is assign-
ed to one of the four computers in the command mode and the remaining com-
puters operate in the listen mode for that bus. Each computer has the ab-
ility to receive data with the other three computers, pass data to the oth-
ers, request data from the others, and perform any other tasks required to
operate the redundant set. No vehicle systems are connected to these
buses.
The flight-critical buses are directed into groups of four to be com-
patible with the grouping of the four computers. Commands to flight deck
crew flight control system (dedicated) displays and the forward GN&C sys-
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 8 of 18
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tem as well as the data from the forward GN&C sensors are transmitted and
received over one group of buses (flight-critical FC-1 through FC-4). The
data commands to the aft GN&C system, as well as the data from the aft
GN&C components, are transmitted and received over FC-5 through FC-8 bus-
es. Each bus in a group is assigned to a separate computer operating in a
command mode. The computer in the command mode issues data requests and
commands to the applicable vehicle systems over its assigned FC (dedicat-
ed) bus. The remaining three buses in each group are assigned to the re-
maining computers to operate in listen mode. A computer operating in lis-
ten mode can only receive data. Thus if Computer 1 operates in command
mode on bus FC-1, it listens on the three remaining buses. In this manner,
each computer commands on one bus of a flight-critical group and listens
on the remaining three.
Each flight-critical bus is a group of four is commanded by a differ-
ent computer. There are multiple units of each GN&C hardware item (sen-
sors, controllers, flight control effector) and each unit is wired to a
different MDM and flight-critical bus. The MDM and bus can be assigned to
another computer. The flight computer operating system in systems soft-
ware in each of the redundant set computers activates a GN&C executive pro-
gram and issues commands to the bus and MDM to provide a set of input da-
ta. Each MDM receives the command from the computer assign to it, acquires
the requested data from the GN&C hardware wired to it, and sends the data
to all four computers.
When the sets of GN&C hardware data arrive at the computers via the
MDM's and data buses, the data generally not in the proper format, units,
or form for use by flight control, guidance, or navigation. A subsystem
operating program for each type of hardware processes the data to make it
usable by GN&C software. These programs contain the software necessary for
hardware operation, activation, self-testing, and moding. The level of re-
dundancy varies from two to four depending on the particular unit. The
software which processes data from the redundant GN&C hardware is called
redundancy management. This performs two functions: selects, from redun-
dant sets of hardware data, one set of data for use by flight control, gui-
dance, and navigation; and detects data which is out of tolerance, identi-
fies the faulty unit, and announces the failure to the flight crew and to
the data collection software.
In the case of the four hardware units, the redundancy management soft-
ware utilizes three and holds the fourth in reserve and utilizes a middle
value select until one of the three is bad, then uses the fourth. If one
of the remaining three is lost, it would downmode to two and use the aver-
age of the two. If one of the remaining two were lost it would downmode to
one and pass the only data it receives.
The three engine interface units between the computers and the three
main engine controllers accept computer main engine commands, reformat
them, and transfer them to each main engine controller. In return, the
engine interface units accept data from the main engine controller, refor-
mat it, and transfer it to computers and operational instrumentation. Main
engine functions such as ignition, gimbaling, throttling, and shutdown are
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 9 of 18
---------------------------------------------------------------------------
controlled by the main engine controller internally through inputs from
the guidance equations which are computed in the orbiter computers.
During non-critical flight periods in orbit, only one or two computers
are used for GN&C tasks and another for payload operations and system man-
agement. The remaining three can be used either for payload management or
deactivated on standby.
The fifth onboard computer is used as a GN&C backup in the initial de-
velopment flights; however it also provides unique functions such as sys-
tem non-critical function monitoring and payload command and monitoring.
The fifth computer has a separate independent software design and coding
activity to protect against generic software failures in the primary com-
puter set.
The payload in the orbiter may have up to five safety-critical status
parameters hardwired, so that these parameters can be recorded as a part
of the orbiter's system management which is transmitted and received over
the two payload buses. To accommodate the various forms of payload data,
the payload data interleaver integrates payload data into the orbiter avi-
onics so it can be transmitted to ground telemetery.
The two master events controllers under computer control provide sig-
nals for arming and safing pyrotechnics, and for command and fire signals
for pyrotechnics in separation processes.
Data bus isolation amplifiers are the interfacing device among the
GSE, the solid rocket booster MDM's and the orbiter launch data bus. They
transmit or receive multiplexed data in any direction. The amplifiers en-
able multiplexed communications over the longer data bus cables which con-
nect the orbiter and GSE. The receiving section of the amplifiers detects
low-level coded signals, discriminates against noise, and decodes the sig-
nal to standard digital data at very low bit error rate; the transmit sec-
tion of the amplifiers then re-encodes the data and retransmits it at full
amplitude and low noise.
Data bus couplers couple the vehicle multiplexed data and control sig-
nals between the data bus and cable studs connected to the various elec-
tronic units. The couplers also provide impedance matching on the data
bus, line termination, dc isolation, and noise rejection.
Each CPU is 193 millimeters (7-1/2 inches) high, 257 millimeters (10-
1/8 inches) wide, 497 millimeters (19-1/2 inches) long and weighs 25.85
kilograms (57 pounds). The IOPs are identical in size and weight to the
CPU's.
Each of the two mass memories is 193 millimeters (7-1/2 inches) high,
294 millimeters (11-1/2 inches) wide, and 381 millimeters (15 inches) long
and weighs 9.97 kilograms (22 pounds). The MDM's are 330 by 254 by 177
millimeters (13 by 10 by 7 inches) and weigh 16.64 kilograms (36.7 pounds)
each. The data bus isolation amplifiers are each 177 by 152 by 127 milli-
meters (7 by 6 by 5 inches) and weigh 3.4 kilograms (7-1/2 pounds). Each
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 10 of 18
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data bus coupler is 16.39 cubic centimeters (one cubic inch) in size and
weighs less than 28 grams (one ounce).
The five CPU's and IOP's are located in the crew compartment mid deck
avionics bays 1,2, and 3 and are cooled by fans. The mass memories are lo-
cated in the crew compartment mid deck avionics bays 2 and 3; each MM is
mounted on a coldplate and cooled by a water loop.
The forward flight-critical MDM's are located in the crew compartment
mid deck avionics bays 1, 2, and 3. They also are mounted on coldplates
and cooled by a water loop. The aft flight-critical MDM's are located in
the aft fuselage avionics bays, are mounted on coldplates, and cooled by
Freon-21 coolant loops.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 11 of 18
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INSTRUMENTATION
The instrumentation system consists of transducers, signal condition-
ers, pulse code modulation encoding equipment, frequency multiplexing e-
quipment, PCM recorders, analog recorders, timing equipment, and onboard
checkout equipment. The instrumentation system is made up of two separate
functional systems: operational instrumentation (OI), and developmental
flight instrumentation (DFI), DFI will be used only for the initial devel-
opment flights. The OI and DFI systems interface with companion compon-
ents, other avionics systems, external tank, solid rocket boosters, and
ground support equipment.
The OI system senses and acquires, conditions, digitizes, formats, and
distributes data for display, telemetry, recording, and checkout. It pro-
vides for PCM recording, voice recording, and master timing for onboard
systems. The equipment consists of two pulse code modulation master units
(PCMMU's), two operations recorders, master timing unit, and various multi-
plexer/demultiplexers (MDM's), signal conditioners, and sensors.
The DFI system provides additional instrumentation for the initial de-
velopment flights. The system senses and acquires, conditions, digitizes,
formats, frequency-multiplexes, distributes, and records data. Its equip-
ment consists of two PCMMU's, three recorders, none frequency division mul-
tiplexers, and various MDM's, signal conditioners, and sensors.
The dedicated signal conditioners (DSC's) provide inputs to the OI and
DFI from such transducer signals as frequency, voltage, current, pressure,
temperature (variable resistance and thermocouple), and displacement (po-
tentiometer), 28 and 5 Vdc discretes. The signal conditioners convert
their input signals to an analog signal of 0 to 5 volts dc or to a 25 or 5
volt dc discrete output signal.
The output signals of the OI DSC's are directed to the flight deck
crew displays, C/W system, and a corresponding MDM. The MDM's convert the
analog signal to serial digital data (a digitized representation of the ap-
plied voltage). The MDM's send this serial digital data to a PCMMU upon re-
quest through the OI data buses. When the MDM is addressed by the PCMMU,
the MDM will select, digitize, and send the requested data to the PCMMU in
serial digital form.
The OI PCMMU receives digital data from the OI MDM's, in addition to
computer downlist data from the onboard computers, and combines them to
form the PCM telemetry for the S-band downlink. The PCMMU controls the
data received from the MDM's; downlist data from the computers is under
the control of flight software. All data received by the PCMMU is stored
in memory and periodically updated. The PCMMU also sends data to the on-
board computers on request.
The OI PCMMU has two formatter memories: programmable read only and
random access (RAM). The former is programmed only before launch; the lat-
ter is reprogrammed several times during flight. The PCMMU will use the
format memories to downlink data from the computers and data from the OI
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 12 of 18
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MDM's into high-rate (128 kbps) and low rate (64 kbps) PCM telemetry data
streams. These data streams are sent to the network signal processor,
which then sends the 128 kbps data to the operations recorders and either
the 128 kbps or 64 kbps data to the S-band transponder for transmission to
the ground. In later flights, the Ku-band transmitter will be used when
the orbiter is in orbit. On the ground this data is recorded again and al-
so monitored in real time at the Mission Control Center, Houston.
Only one of the redundant OI PCMMU's and network signal processors op-
erates at a time. The ones used are controlled by the crew through the
flight deck display and control panel.
It is noted that the primary port of an MDM operates with PCMMU 1 and
the secondary port of an MDM operates with PCMMU 2.
On later flights, a payload data interleaver will accept data simulta-
neously from up to five attached and one detached payload, interleave it,
and send it to the PCMMU. The input data is in serial digital data
streams. Data temporarily stored in the PCMMU memory can be accessed by
the PCMMU telemetry formatter and by onboard computers. The payload data
interleaver is programmed on board from mass memory via the computers to
select specific data from each payload PCM signal and store it within its
buffer memory locations.
The OI PCMMU's receive a synchronization clock signal from the master
timing unit. If this signal is not present, the PCMMU provides its own ti-
ming and continues to provide timing signals to the payload data interleav-
er and network signal processor.
There are many different PCM telemetry formats that control the meas-
urement groupings the PCMMU assembles into the 128 kbps and 64 kbps data
streams for different mission phases. Those to be used for each mission
are stored in the onboard computer's mass memory. When the ground or
flight crew want to change the format, a command is sent to the computers,
which will then load the desired format from mass memory into the format-
ter RAM of the PCMMU.
The five onboard computers are capable of data processing. They per-
form programmed computations and then prepare the data for telemetry trans-
mission by means of a downlist. Four of the computers to the primary
flight control system in the orbiter and provide primary downlist data.
The fifth computer is assigned to the backup flight control system in the
initial development flights and to systems management and payload manage-
ment in later flights and provides downlist data. The computer downlist da-
ta consists of a table of values compiled in the computer. The format can
be changed by ground command or by the flight crew. The downlist data is
sent from the computers to the PCMMU, where it is combined with operation-
al instrumentation data to form the PCM downlink data stream.
The network signal processor receives the PCMMU 128 kbps and 64 kbps
telemetry data streams and also one or two analog voice channels from the
orbiter audio central control unit. The processor converts the analog
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 13 of 18
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voice signals to digital voice signals, time-division multiplexes them
with the PCM telemetry data, and sends the composite signal to the S-band
transponder for downlink transmission. The total data rate of the compos-
ite signal will be either 192 kbps (high rate) or 96 kbps (low rate). The
128 kbps telemetry plus two 32 kbps voice channels equal the 192 kbps to-
tal. The 64 kbps telemetry plus one 32 kbps voice channel equal 96 kbps
total. The downlink rate from the network signal processor can be switched
by ground command at any point in the data cycle. The processor also out-
puts to the recorders either the 128 kbps telemetry or the 192 kbps compos-
ite signal. Only one processor operates at a time.
The DFI dedicated signal conditioners' output signals are directed to
the DFI multiplexer-demultiplexer, which convert them into serial data and
send them via the DFI data buses to the DFI PCMMU. The DFI PCMMU formats
the data into a 128 kbps data stream and outputs it to a DFI PCM recorder
and to a special frequency division multiplexer. The latter is used to
transmit the data to ground stations on the DFI S-band FM transmitter and
the S-band downlink. On the ground, this data is recorded again and sel-
ected parameters are sent to the Mission Control Center in Houston for
real-time monitoring.
The DFI PCMMU also receives timing from the master timing unit; how-
ever, it will provide its own timing if the signal is not present. Only
one of the redundant DFI PCMMU's operates at a time, the one in use sel-
ected by the flight crew.
Wideband signal conditioners provide input signals to the DFI MDM's,
accommodate low level accelerometer, vibration, and acoustic signals, con-
vert them, and send an analog output signal of 0 to 5 volts dc to the ap-
plicable frequency division multiplexer.
The strain gauge signal conditioners in the DFI accommodate low level
signals from the strain gauges, convert them, and provide an analog output
signal of 0 to 5 volts dc. Selected strain gauge analog signals are sent
to a corresponding MDM which converts the analog signal into a digital ser-
ial output. The digital serial output is received by the DFI data buses
and transmitted to the DFI PCMMU which formats the data into the 128 kbps
data stream. Other strain gauge signal conditioners send an analog signal
of 0 to 5 volts dc to a corresponding FDM.
The nine DFI MDM's frequency multiplex the analog data for wideband re-
cording to the wideband ascent recorder and wideband mission recorder. The
FDM FMF-1 receives 128 kbps digital PCM data from the DFI PCMMU as well as
15 selected analog inputs from various signal conditioners. FDM FMF-1
sends the multiplexed composite signal to the DFI S-band FM transmitter
for transmission to the ground stations on the S-band DFI FM downlink. The
composite is also sent to the ascent and mission recorders.
MASTER TIMING UNIT. The master timing unit is a stable crystal-con-
trolled timing source for the orbiter. It provides serial time reference
signals to the onboard computers, PCMMU's, FDM's, and various time display
panels. It also provides synchronization to instrumentation and other sys-
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 14 of 18
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tems. It includes separate time accumulators for Greenwhich mean time
(GMT) and mission elapsed time (MET), which can be reset or updated from
the ground via uplink through the onboard computer or by the flight crew
through the use of their flight deck display and control panel keyboard
and CRT (cathode ray tube) time displays.
The signal flows from the 4.608 MHz oscillators to the output of the
GMT and MET accumulators. The three independent GMT and three independent
MET counters operate simultaneously. Separate time accumulators are used
for each GMT and MET clock, and they accumulate time in days, hours, min-
utes, seconds, and milliseconds. The GMT capability is 366 days, 23 hours,
59 minutes, 59 seconds, and 999.875 milliseconds. For MET, the capability
is 365 days, 23 hours, 59 minutes, 59 seconds, and 999.875 milliseconds.
Both can be updated and reset by ground equipment before flight or from
the onboard controls by flight crew. During flight, the GMT and MET accumu-
lators are updated at a predetermined time by uplink and onboard computer
or by voice command and entered through the flight deck display and con-
trol panel keyboard and CRT display.
FREQUENCY MODULATION SIGNAL PROCESSOR. The FM signal processor re-
ceives inputs and processes data from three sources: the three engine in-
terface units, the video switching unit, and the recorder dump from the op-
erations recorders. It is commanded to select one of these sources at a
time for ground output to the S-band FM transmitter for transmission to
the ground stations on the S-band FM downlink. The output is then either
three channels of main engine data at 60 kbps each, real-time television
from the onboard TV cameras, or operations recorder dumps (128 kbps PCM
telemetry), 192 kbps composite data, or one channel of main engine data at
60 kbps.
OPERATIONS RECORDERS. There are two of these recorders (also refer-
red to as maintenance/loop recorders) used for serial recording and dump-
ing of digital voice and PCM data. The recorders normally are controlled
by ground command, but they can be commanded by the flight crew through
the flight deck display and control panel keyboard or by switches on the
recorder panel. Input to the recorders is from the network signal proces-
sor, either 128 kbps PCM data or a 192 kbps composite signal which in-
cludes the 128 kbps PCM data and two 32 kbps voice channels. The network
signal processor receives the PCM data from the OI PCMMU and the voice sig-
nals from the audio control center. In addition, operations recorder No. 1
receives three channels of main engine data at 60 kbps during ascent.
In the maintenance/loop mode, one is selected as a maintenance record-
er while the other is designated a loop recorder. The latter records the
serial output of the OI PCMMU continually for temporary storage. This data
is recorded in loop fashion by switching sequentially through tracks 12,
13, and 14. The loop recorder also will record digital data from the three
engine interface units at 60 kbps during ascent, but not simultaneously
with the loop function. The maintenance recorder is used for permanent
storage of two types of data: anomaly data from the loop recorder dump,
and quick-look PCM data. When the 11th track of the 14 data tracks on the
maintenance recorder is filled, it sends a signal to alert the user to in-
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 15 of 18
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terchange the loop and maintenance functions between the two recorders.
The functions of the recorders can be interchanged by uplink commands via
the network signal processor or by the flight crew.
The operations recorders can be commanded to dump recorded data from
one recorder while continuing to record real-time data on the other. The
dump data is sent to the FM signal processor for transmission to the
ground station via the S-band FM transmitter on the S-band FM downlink.
When the ground has verified that the data they received is valid, the op-
erations recorders can use that part of the tape to record new data.
A single recorder can store and reproduce digital and analog data both
singly and in combination at many rates.
The single recorder function will be used for the first development
flight; however, both recorders may be operated in a maintenance/loop func-
tion.
Recorder functions can be summarized as follows:
Data In, Recorder No. 1
Accepts three parallel channels of engine data at 60 kbps
during ascent
Accepts 128/192 kbps of interleaved PCM data and voice which
serially sequences from Track 4 to Track 14
Accepts real-time data from network signal processor (plus
voice in development flights). Recording time is 32 min-
utes for parallel record and 5.8 hours for serial re-
cord on Tracks 4 through 14 at 381 millimeters (15 inch-
es) per second.
Data In, Recorder No. 2
Accepts 128/192 kbps of interleaved PCM voice and data which
serially sequences from Track 1 through Track 14.
Accepts real-time data from network signal processor (plus
voice on development flights). Recording time is 7.5
hours at 381 millimeters (15 inches) per second for se-
rial record on 14 tracks.
Data Out, Recorder No. 1
In-flight playback of engine interface unit data and network
signal processor digital data via S-band FM transponder
and in later flights via Ku-band transmitter.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 16 of 18
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In operational flights, in-flight playback of anomaly PCM
data for maintenance recording; playback of data serial-
ly to GSE T -0 umbilical
Data Out, Recorder No. 2
In-flight playback of digital data via S-band FM transponder
and in later flights via Ku-band transponder.
In operational flights, in-flight playback of anomaly PCM
data for maintenance recording; playback of data serial-
ly to GSE T -0 umbilical.
Recorder Control
Manual control from mission specialist flight deck aft sta-
tion display and control panel. Uplink and onboard com-
puter keyboard control
Recorder speeds of 190, 381, 609, and 3,048 millimeters
(7.5, 15, 24, and 120 inches) per second by hardware
programs plug direct command.
The tape recorders contain a minimum of 731 meters (2,400 feet) of 12
millimeters (0.5 inch) by 1 mil magnetic tape. The operate at 609 milli-
meters (24 inches) per second in the record mode, and 3,048 millimeters
(120 inches) per second in playback mode.
PAYLOAD RECORDER. The payload recorder is not used in the initial
development flights, although it will be on board. It is identical to the
operations recorders in hardware and will be used to record payload data
and dump in flight via the S-band transponder or in later flights the Ku-
band transmitter.
The payload and recorder capabilities are:
Data In:
Accepts digital inputs of 64 kbps either serial or parallel
up to 14 tracks
Accepts analog data from the 1.9 kHz to 2 MHz either serial
or parallel up to 14 tracks.
Serial/parallel track programming is determined by permis-
sion payload distribution panel wiring.
Record time is 32 minutes for parallel record or 7.5 hours
for serial record at 381 millimeters (15 inches) per
second.
Data Out:
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 17 of 18
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In-flight playback of digital data via S-band transponder or
in later flights via Ku-band transmitter.
In-flight playback (analog/digital) data to payload payload
distribution panel; playback of data to GSE via T -0
umbilical.
Control
Manual control from mission specialist flight deck aft sta-
tion display and control panel
Uplink and computer keyboard by computers. Recorder speeds
of 381, 609, and 3,048 millimeters (15, 24, and 120
inches) per second by hardware program plug. Recorder
hardwired for continuous run modes.
DFI RECORDERS. Three recorders are used in the DFI system to pro-
vide PCM and wideband recording: PCM, wideband and ascent, and wideband
mission recorders. The operations of these recorders can be controlled
only by the flight crew through the use of switches on the flight deck dis-
play and control panels. The DFI recorders cannot be dumped in flight;
they are played back via the GSE T -0 umbilical after the orbiter has land-
ed.
The PCM recorder is used to record 128 kbps PCM data from the DFI
PCMMU.
The two wideband recorders are used to record the output of the fre-
quency division multiplexers. The wideband ascent recorder will operate
during ascent only.
It will record either continually or in one of two automatically timed
intervals selected by the crew. The two intervals are a high-sample mode,
which automatically turns the recorder on for 10 seconds, off for five min-
utes, on again for 10 seconds, etc., and low sample mode, which automatic-
ally turns the recorder on for 10 seconds, off for 10 minutes, etc. The
purpose of this switching is to save tape. The recorder has 14 tracks
which are recorded serially, and each track will fill up in 32 minutes.
This means that the recorder can be operated for a total period of about
7-1/2 hours.
All its tracks record in parallel. It will operate for only 32 min-
utes before all tracks become full. When the recorder reaches the end of
the tape, it will shut itself off automatically and will not be used again
during the flight.
The wideband mission recorder can be operated only in continuous mode
or shut off by a switch on the flight deck display and control panel. It
can be operated only for a total of two hours before all the tracks become
full.
PRESS INFORMATION
SPACE SHUTTLE TRANSPORTATION SYSTEM
March 1982
Rockwell International
SPACE SHUTTLE SPACECRAFT SYSTEMS
AVIONICS SYSTEMS Page 18 of 18
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EQUIPMENT LOCATION. Instrumentation equipment, except for sensors
and selected dedicated signal conditioners, are located in the forward and
aft avionics bays. The DFI equipment is installed in the aft avionics bays
and special containers located in the forward fuselage mid-deck crew com-
partment and the mid fuselage. Sensors and dedicated signal conditioners
are located throughout the orbiter in areas selected on the basis of acces-
sibility, minimum harness requirements, and functional requirements. Ef-
fective use of remote data acquisition techniques was considered for optim-
izing equipment location. The factors which were considered in determin-
ing equipment location were weight, power, physical size, redundancy, and
wire density and length to each compartment and interconnect wiring.
The abbreviation OA refers to operational, aft, OF to operational for-
ward, OL to operational left, OR to operational right, OM to operational
mid, DF to development forward, DL to development left, DR to development
right, FMF to frequency multiplexer forward, FMC to frequency multiplexer
center, FMR to frequency multiplexer center, FMR to frequency multiplexer
right, DL to development left, DR to development right, and DC to develop-
ment center.
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