Saturn V Instrument Unit
Encyclopedia
The Saturn V Instrument Unit is a ring-shaped structure fitted to the top of the Saturn V
rocket's third stage (S-IVB
) and the Saturn IB
's second stage (S-IVB). It was immediately below the SLA (Spacecraft/Lunar Module Adapter) panels that contained the Lunar Module. The Instrument Unit contains the guidance system for the Saturn V rocket. Some of the electronics contained within the Instrument Unit are a digital computer, analog flight control computer, emergency detection system, inertial guidance platform, control accelerometers and control rate gyros. The instrument unit (IU) for Saturn V was designed by NASA at Marshall Space Flight Center (MSFC) and was developed from the Saturn I IU. NASA's contractor to construct the Saturn V Instrument Unit was International Business Machines (IBM
).
One of the unused Instrument Units is currently on display at the Steven F. Udvar-Hazy Center
in Chantilly, Virginia
. The plaque for the Unit has the following description:
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The IU made its debut with SA-5, the first Saturn I Block II launch. The first version of the IU was 154 inches (3,911.6 mm) in diameter and 58 inches (1,473.2 mm) high, and was both designed and built by MSFC. Guidance, telemetry, tracking and power components were contained in four pressurized, cylindrical containers attached like spokes to a central hub.
MSFC flew version 2 of the IU on SA-8, 9 and 10. Version 2 was the same diameter as version 1, but only 34 inches (863.6 mm) high. Instead of pressurized containers, the components were hung on the inside of the cylindrical wall, achieving a reduction in weight.
The last version, number 3, was 260 inches (6,604 mm) in diameter and 36 inches (914.4 mm) tall. It was designed by MSFC but manufactured by IBM in their factory at Huntsville, and flew on all Saturn IB and Saturn V launches. This is the version that is on display in Washington, Huntsville, Houston, and the Apollo/Saturn V Center.
After clearing the launch tower, a flight program stored in the launch vehicle digital computer (LVDC) commanded a roll of the vehicle to orient it so that the subsequent pitch maneuver pointed the vehicle in the desired azimuth. The roll and pitch commands were controlled by the stored program, and were not affected by navigation measurements. Until the end of the S-IC burn, guidance commands were functions only of time.
First stage cutoff and stage separation were commanded when the IU received a signal that the tank's fuel level had reached a predetermined point. Guidance during the second and third stage burns depended both on time and navigation measurements, in order to achieve the target orbit using the minimum fuel.
Second stage engine cutoff was commanded by the IU at a pre-determined fuel level, and the stage was separated. By this time, the vehicle had reached its approximate orbital altitude, and the third stage burn was just long enough to reach a circular parking orbit
.
During manned Apollo missions, the vehicle coasted in Earth orbit for 2-4 passes as the crew performed checks of systems status and other tasks, and as ground stations tracked the vehicle. During the hour and a half after launch, tracking stations around the world had refined estimates of the vehicle's position and velocity, collectively known as its state vector. The latest estimates were relayed to the guidance systems in the IU, and to the Command Module Computer in the spacecraft. When the Moon, Earth, and vehicle were in the optimum geometrical configuration, the third stage was reignited to put the vehicle into a translunar orbit. For Apollo 15, for example, this burn lasted 5 minutes 55 seconds.
After translunar injection came the maneuver called transposition, docking, and extraction. This was under crew control, but the IU held the S-IVB/IU vehicle steady while the Command/Service Module (CSM) first separated from the vehicle, rotated 180 degrees, and returned to dock with the Lunar Module (LM). When the CSM and LM had "hard docked" (connected by a dozen latches), the rearranged spacecraft separated from the S-IVB/IU.
The last function of the IU was to command the very small maneuver necessary to keep the S-IVB/IU out of the way of the spacecraft. On some missions the S-IVB/IU went into high Earth or Solar orbit, while on others it was crashed into the Moon; seismometers were left on the Moon during Apollo 11, 12, 14, 15, and 16, and the S-IVB/IUs of Apollo 13, 14, 15, 16, and 17 were directed to crash. These impacts provided impulses that were recorded by the seismometer network to yield information about the geological structure of the Moon.
The IU consists of six subsystems: structure, guidance and control, environmental control, emergency detection, radio communications (for telemetry, tracking, and command), and power.
The IU is divided into 24 locations, which are marked on the interior by numbers 1-24 on the aluminum surface just above the blue flange.
The Saturn V launch vehicle was guided by navigation, guidance, and control equipment located in the IU. A space stabilized platform (the ST-124-M3 inertial platform
at location 21) measured acceleration and attitude. A launch vehicle digital computer (LVDC at location 19) solved guidance equations, and an analog flight control computer (location 16) issued commands to steer the vehicle.
The attitude of the vehicle was defined in terms of three axes:
The ST-124-M3 inertial platform
contains three gimbal
s: the outer gimbal (which can rotate 360° about the roll or X axis of the vehicle), the middle gimbal (which can rotate ±45° about the yaw or Z axis of the vehicle), and the inner or inertial gimbal (which can rotate 360° about the pitch or Y axis of the vehicle). The inner gimbal is a platform to which is fixed several components:
The angular positions of gimbals on their axes were measured by resolvers, which sent their signals to the LVDA. The LVDA was the input/output device for the LVDC. It performed the necessary processing of signals to make these signals acceptable to the LVDC.
The instantaneous attitude of the vehicle was compared with the desired vehicle attitude in the LVDC. Attitude correction signals from the LVDC were converted into control commands by the flight control computer. The required thrust direction was obtained by gimbaling the engines in the propelling stage to change the thrust direction of the vehicle. Gimbaling of these engines was accomplished through hydraulic actuator
s. In the first and second stages (S-IC and S-II), the four outboard engines were gimbaled to control roll, pitch, and yaw. Since the third (S-IVB) stage has only one engine, an auxiliary propulsion system was used for roll control during powered flight. The auxiliary propulsion system provides complete attitude control during coast flight of the S-IUB/IU stage.
The cooling fluid circulated through the TCS was a mixture of 60 percent methanol
and 40 percent demineralized water
by weight. Each cold plate was capable of dissipating at least 420 watts.
During flight, heat generated by equipment mounted on the cold plates was dissipated to space by a sublimation heat exchanger
. Water from a reservoir (water accumulator) was exposed to the low temperature and pressure environment of space, where it first freezes and then sublimates, taking heat from the heat exchanger and transferring it to the water molecules which escape to space in gaseous state. Water/methanol was cooled by circulation through the heat exchanger.
). This sphere is 21 inches (0,53 m) in diameter and is mounted at location 22, to the left of the ST-124-M3. Gas from the supply sphere passes through a filter, a pressure regulator, and a heat exchanger before flowing through the bearings in the stable platform.
at four locations: between panels 1 and 2, 7 and 8, 13 and 14, and 19 and 20. Tubes lead from these locations to location 7, where they were connected to ground support equipment (external to the IU) which can detect hazardous gases.
The EDS was distributed throughout the vehicle and includes some components in the IU. There were nine EDS rate gyros installed at location 15 in the IU. Three gyros monitored each of the three axes (pitch, roll and yaw), providing triple redundancy. The control signal processor (location 15) provided power to and received inputs from the nine EDS rate gyros. These inputs were processed and sent to the EDS distributor (location 14) and to the flight control computer (location 16). The EDS distributor served as a junction box and switching device to furnish the spacecraft display panels with emergency signals if emergency conditions existed. It also contained relay and diode logic for the automatic abort sequence. An electronic timer (location 17) was activated at liftoff and 30 seconds later energized relays in the EDS distributor which allowed multiple engine shutdown. This function was inhibited during the first 30 seconds of launch, to preclude the vehicle falling back into the launch area. While the automatic abort was inhibited, the flight crew can initiate a manual abort if an angular-overrate or two-engine-out condition arose.
Parameters measured include acceleration
, angular velocity
, flow rate, position, pressure
, temperature
, voltage
, current
, frequency
, and others. Sensor
signals were conditioned by amplifier
s or converter
s located in measuring racks. There are four measuring racks in the IU at locations 1, 9, and 15 and twenty signal conditioning modules in each. Conditioned signals were routed to their assigned telemetry channel by the measuring distributor at location 10. There were two telemetry links. In order for the two IU telemetry links to handle approximately 200 separate measurements, these links must be shared. Both frequency sharing and time sharing multiplexing
techniques were used to accomplish this. The two modulation
techniques used were pulse code modulation/frequency modulation (PCM/FM) and frequency modulation/frequency modulation (FM/FM).
Two Model 270 time sharing multiplexer
s (MUX-270) were used in the IU telemetry system, mounted at locations 9 and 10. Each one operates as a 30x120 multiplexer (30 primary channels, each sampled 120 times per second) with provisions for submultiplexing individual primary channels to form 10 subchannels each sampled at 12 times per second. Outputs from the MUX-270 go to the PCM/DDAS assembly model 301 at location 12, which in turn drives the 245.3 MHz PCM VHF transmitter.
The FM/FM signals were carried in 28 subcarrier channels and transmitted by a 250.7 MHz FM transmitter.
Both the FM/FM and the PCM/FM channels were coupled to the two telemetry antennas on opposite sides of the IU outside locations 10 and 22.
transponder
s carried by the IU provided tracking data to the ground which were used to determine the vehicle's trajectory
. The transponder received coded or single pulse interrogation from ground stations and transmitted a single-pulse reply in the same frequency band (5.4 to 5.9 GHz
). A common antenna
was used for receiving and transmitting, The C-band transponder antennas are outside locations 11 and 23, immediately below CCS PCM omni receive antennas.
, Houston, and was sent to remote stations for transmission to the launch vehicle. Command messages were transmitted from the ground at 2101.8 MHz. The received message was passed to the command decoder
(location 18), where it was checked for authenticity before being passed to the LVDC. Verification of message receipt was accomplished through the IU PCM telemetry system. The CCS system used five antennas:
The first IU flew on the fifth Saturn launch, SA-5, and was 12 in 10 in (3.91 m) in diameter and 4 in 10 in (1.47 m) high. The components it carried were in pressurized containers. This version flew on SA-5, SA-6 and SA-7. The IU carried by missions SA-8, -9, and -10 was only 2 in 10 in (0.8636 m) high, and was not pressurized.
With the Saturn IB and Saturn V launches, a third version was used, 21.6 feet (6.6 m) in diameter and 3 foot (0.9144 m) high. Comparison of these photographs of the Instrument Unit shows that the configuration of components carried by this version changed, depending on the mission. Some equipment was deleted (e.g. the Azusa tracking system was deleted from later IUs), some equipment was added (e.g. a fourth battery for longer missions), and other components were moved around.
These images also show that some components (e.g. batteries, the ST-124 inertial platform) were installed in the IU after it had been stacked in the VAB on top of the S-IVB third stage.
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
rocket's third stage (S-IVB
S-IVB
The S-IVB was built by the Douglas Aircraft Company and served as the third stage on the Saturn V and second stage on the Saturn IB. It had one J-2 engine...
) and the Saturn IB
Saturn IB
The Saturn IB was an American launch vehicle commissioned by the National Aeronautics and Space Administration for use in the Apollo program...
's second stage (S-IVB). It was immediately below the SLA (Spacecraft/Lunar Module Adapter) panels that contained the Lunar Module. The Instrument Unit contains the guidance system for the Saturn V rocket. Some of the electronics contained within the Instrument Unit are a digital computer, analog flight control computer, emergency detection system, inertial guidance platform, control accelerometers and control rate gyros. The instrument unit (IU) for Saturn V was designed by NASA at Marshall Space Flight Center (MSFC) and was developed from the Saturn I IU. NASA's contractor to construct the Saturn V Instrument Unit was International Business Machines (IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
).
One of the unused Instrument Units is currently on display at the Steven F. Udvar-Hazy Center
Steven F. Udvar-Hazy Center
The Steven F. Udvar-Hazy Center is the Smithsonian National Air and Space Museum 's annex at Washington Dulles International Airport in the Chantilly area of Fairfax County, Virginia, United States....
in Chantilly, Virginia
Chantilly, Virginia
Chantilly is an unincorporated community located in western Fairfax County and southeastern Loudoun County of Northern Virginia. Recognized by the U.S. Census Bureau as a census designated place , the community population was 23,039 as of the 2010 census -- down from 41,041 in 2000, due to the...
. The plaque for the Unit has the following description:
The Saturn V rocket, which sent astronauts to the Moon, used inertial guidance, a self-contained system that guided the rocket's trajectory. The rocket booster had a guidance system separate from those on the command and lunar modules. It was contained in an instrument unit like this one, a ring located between the rocket's third stage and the command and lunar modules. The ring contained the basic guidance system components—a stable platform, accelerometers, a digital computer, and control electronics—as well as radar, telemetry, and other units.
The instrument unit's stable platform was based on an experimental unit for the German V-2 rocket of World War II. The Bendix Corporation produced the platform, while IBM designed and built the unit's digital computer.
Instrument Unit specifications
- Diameter: 260 inches (6.6 m)
- Height: 36 inches (914 mm)
- Weight at launch: ~4,400 lb (1996 kg)
Mission history
There was no Instrument Unit for Saturn I Block I boosters (SA-1 to SA-4). Guidance and control equipment was carried in canisters on top of the S-I first stage, and included the ST-90 stabilized platform, made by Ford Instrument Company and used in the Redstone missile.The IU made its debut with SA-5, the first Saturn I Block II launch. The first version of the IU was 154 inches (3,911.6 mm) in diameter and 58 inches (1,473.2 mm) high, and was both designed and built by MSFC. Guidance, telemetry, tracking and power components were contained in four pressurized, cylindrical containers attached like spokes to a central hub.
MSFC flew version 2 of the IU on SA-8, 9 and 10. Version 2 was the same diameter as version 1, but only 34 inches (863.6 mm) high. Instead of pressurized containers, the components were hung on the inside of the cylindrical wall, achieving a reduction in weight.
The last version, number 3, was 260 inches (6,604 mm) in diameter and 36 inches (914.4 mm) tall. It was designed by MSFC but manufactured by IBM in their factory at Huntsville, and flew on all Saturn IB and Saturn V launches. This is the version that is on display in Washington, Huntsville, Houston, and the Apollo/Saturn V Center.
| PROGRAM | VEHICLE | MISSION | LAUNCH DATE | PAD | IU VERSION |
|---|---|---|---|---|---|
| Saturn I Saturn I The Saturn I was the United States' first heavy-lift dedicated space launcher, a rocket designed specifically to launch large payloads into low Earth orbit. Most of the rocket's power came from a clustered lower stage consisting of tanks taken from older rocket designs and strapped together to make... |
SA-1 | SA-1 SA-1 (Apollo) SA-1 was the first Saturn I space launch vehicle, the first in the Saturn family, and was part of the American Apollo program. The rocket was launched on October 27, 1961 from Cape Canaveral, Florida.-Objectives:... |
27-Oct-61 | 34 | - |
| Saturn I | SA-2 | SA-2 SA-2 (Apollo) SA-2 was the second flight of the Saturn I launch vehicle, the first flight of Project Highwater, and was part of the American Apollo program. The rocket was launched on April 25, 1962 from Cape Canaveral, Florida.-Objectives:... |
25-Apr-62 | 34 | - |
| Saturn I | SA-3 | SA-3 SA-3 (Apollo) SA-3 was the third flight Saturn I launch vehicle, the second flight of Project Highwater and was part of the Apollo Program.-Objectives:... |
16-Nov-62 | 34 | - |
| Saturn I | SA-4 | SA-4 SA-4 (Apollo) SA-4 was the fourth launch of a Saturn I launch vehicle and the last of the initial test phase of the first stage. It was part of the Apollo Program.-Objectives:SA-4 was the last flight to test only the S-I first stage of the Saturn I rocket... |
28-Mar-63 | 34 | - |
| Saturn I | SA-5 | SA-5 SA-5 (Apollo) SA-5 was the first launch of the Block II Saturn I rocket and was part of the Apollo Program.-Upgrades and objectives:The major changes that occurred on SA-5 were that for the first time the Saturn I would fly with two stages - the S-I first stage and the S-IV second stage. The second stage... |
29-Jan-64 | 37B | 1 |
| Saturn I | SA-6 | A-101 | 28-May-64 | 37B | 1 |
| Saturn I | SA-7 | A-102 | 18-Sep-64 | 37B | 1 |
| Saturn I | SA-9 | A-103 | 16-Feb-65 | 37B | 2 |
| Saturn I | SA-8 | A-104 | 25-May-65 | 37B | 2 |
| Saturn I | SA-10 | A-105 | 30-Jul-65 | 37B | 2 |
| Saturn IB Saturn IB The Saturn IB was an American launch vehicle commissioned by the National Aeronautics and Space Administration for use in the Apollo program... |
SA-201 | AS-201 AS-201 AS-201 , flown February 26, 1966, was the first unmanned test flight of an entire production Block I Apollo Command/Service Module and the Saturn IB launch vehicle. The spacecraft consisted of the second Block I command module and the first Block I service module... |
26-Feb-66 | 34 | 3 |
| Saturn IB | SA-203 | AS-203 AS-203 AS-203 was an unmanned flight of the Saturn IB rocket on July 5, 1966. It carried no Apollo Command/Service Module spacecraft, as its purpose was to verify the design of the S-IVB rocket stage restart capability that would later be used in the Apollo program to boost astronauts from Earth orbit to... |
5-Jul-66 | 37B | 3 |
| Saturn IB | SA-202 | AS-202 AS-202 AS-202 was the second unmanned, suborbital test flight of a production Block I Apollo Command/Service Module launched with the Saturn IB launch vehicle. It launched August 25, 1966 and was the first flight which included the spacecraft Guidance and Navigation Control system and fuel cells... |
25-Aug-66 | 34 | 3 |
| Saturn V Saturn V The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload... |
SA-501 | Apollo 4 Apollo 4 Apollo 4, , was the first unmanned test flight of the Saturn V launch vehicle, which was ultimately used by the Apollo program to send the first men to the Moon... |
9-Nov-67 | 39A | 3 |
| Saturn IB | SA-204 | Apollo 5 Apollo 5 Apollo 5 was the first unmanned flight of the Apollo Lunar Module, which would later carry astronauts to the lunar surface. It lifted off on January 22, 1968 with a Saturn IB rocket.-Objectives:... |
22-Jan-68 | 37B | 3 |
| Saturn V | SA-502 | Apollo 6 Apollo 6 Apollo 6, launched on April 4, 1968, was the Apollo program's second and last A type mission—unmanned test flight of its Saturn V launch vehicle. It was intended to demonstrate full lunar injection capability of the Saturn V, and the capability of the Command Module's heat shield to withstand a... |
4-Apr-68 | 39A | 3 |
| Saturn IB | SA-205 | Apollo 7 Apollo 7 Apollo 7 was the first manned mission in the American Apollo space program, and the first manned US space flight after a cabin fire killed the crew of what was to have been the first manned mission, AS-204 , during a launch pad test in 1967... |
11-Oct-68 | 34 | 3 |
| Saturn V | SA-503 | Apollo 8 Apollo 8 Apollo 8, the second manned mission in the American Apollo space program, was the first human spaceflight to leave Earth orbit; the first to be captured by and escape from the gravitational field of another celestial body; and the first crewed voyage to return to Earth from another celestial... |
21-Dec-68 | 39A | 3 |
| Saturn V | SA-504 | Apollo 9 Apollo 9 Apollo 9, the third manned mission in the American Apollo space program, was the first flight of the Command/Service Module with the Lunar Module... |
3-Mar-69 | 39A | 3 |
| Saturn V | SA-505 | Apollo 10 Apollo 10 Apollo 10 was the fourth manned mission in the American Apollo space program. It was an F type mission—its purpose was to be a "dry run" for the Apollo 11 mission, testing all of the procedures and components of a Moon landing without actually landing on the Moon itself. The mission included the... |
18-May-69 | 39B | 3 |
| Saturn V | SA-506 | Apollo 11 Apollo 11 In early 1969, Bill Anders accepted a job with the National Space Council effective in August 1969 and announced his retirement as an astronaut. At that point Ken Mattingly was moved from the support crew into parallel training with Anders as backup Command Module Pilot in case Apollo 11 was... |
16-Jul-69 | 39A | 3 |
| Saturn V | SA-507 | Apollo 12 Apollo 12 Apollo 12 was the sixth manned flight in the American Apollo program and the second to land on the Moon . It was launched on November 14, 1969 from the Kennedy Space Center, Florida, four months after Apollo 11. Mission commander Charles "Pete" Conrad and Lunar Module Pilot Alan L... |
14-Nov-69 | 39A | 3 |
| Saturn V | SA-508 | Apollo 13 Apollo 13 Apollo 13 was the seventh manned mission in the American Apollo space program and the third intended to land on the Moon. The craft was launched on April 11, 1970, at 13:13 CST. The landing was aborted after an oxygen tank exploded two days later, crippling the service module upon which the Command... |
11-Apr-70 | 39A | 3 |
| Saturn V | SA-509 | Apollo 14 Apollo 14 Apollo 14 was the eighth manned mission in the American Apollo program, and the third to land on the Moon. It was the last of the "H missions", targeted landings with two-day stays on the Moon with two lunar EVAs, or moonwalks.... |
31-Jan-71 | 39A | 3 |
| Saturn V | SA-510 | Apollo 15 Apollo 15 Apollo 15 was the ninth manned mission in the American Apollo space program, the fourth to land on the Moon and the eighth successful manned mission. It was the first of what were termed "J missions", long duration stays on the Moon with a greater focus on science than had been possible on previous... |
26-Jul-71 | 39A | 3 |
| Saturn V | SA-511 | Apollo 16 Apollo 16 Young and Duke served as the backup crew for Apollo 13; Mattingly was slated to be the Apollo 13 command module pilot until being pulled from the mission due to his exposure to rubella through Duke.-Backup crew:... |
16-Apr-72 | 39A | 3 |
| Saturn V | SA-512 | Apollo 17 Apollo 17 Apollo 17 was the eleventh and final manned mission in the American Apollo space program. Launched at 12:33 a.m. EST on December 7, 1972, with a three-member crew consisting of Commander Eugene Cernan, Command Module Pilot Ronald Evans, and Lunar Module Pilot Harrison Schmitt, Apollo 17 remains the... |
7-Dec-72 | 39A | 3 |
| Saturn V | SA-513 | Skylab 1 | 14-May-73 | 39A | 3 |
| Saturn IB | SA-206 | Skylab 2 Skylab 2 -Backup crew:-Support crew:*Robert L. Crippen*Richard H. Truly*Henry W. Hartsfield, Jr*William E. Thornton-Mission parameters:*Mass: 19,979 kg*Maximum Altitude: 440 km*Distance: 18,536,730.9 km... |
25-May-73 | 39B | 3 |
| Saturn IB | SA-207 | Skylab 3 Skylab 3 Skylab 3 was the second manned mission to Skylab. The Skylab 3 mission started July 28, 1973, with the launch of three astronauts on the Saturn IB rocket, and lasted 59 days, 11 hours and 9 minutes... |
28-Jul-73 | 39B | 3 |
| Saturn IB | SA-208 | Skylab 4 Skylab 4 Skylab 4 was the fourth Skylab mission and placed the third and final crew on board the space station. The mission started November 16, 1973 with the launch of three astronauts on a Saturn IB rocket, and lasted 84 days, 1 hour and 16 minutes... |
16-Nov-73 | 39B | 3 |
| Saturn IB | SA-210 | ASTP Apollo-Soyuz Test Project -Backup crew:-Crew notes:Jack Swigert had originally been assigned as the command module pilot for the ASTP prime crew, but prior to the official announcement he was removed as punishment for his involvement in the Apollo 15 postage stamp scandal.-Soyuz crew:... |
15-Jul-75 | 39B | 3 |
Mission profile
Saturn Apollo flight profiles varied considerably by mission. All missions began, however, with liftoff under power of the first stage. To more smoothly control engine ignition, thrust buildup and liftoff of the vehicle, restraining arms provided support and hold down at four points around the base of the S-IC stage. A gradual controlled release was accomplished during the first six inches of vertical motion.After clearing the launch tower, a flight program stored in the launch vehicle digital computer (LVDC) commanded a roll of the vehicle to orient it so that the subsequent pitch maneuver pointed the vehicle in the desired azimuth. The roll and pitch commands were controlled by the stored program, and were not affected by navigation measurements. Until the end of the S-IC burn, guidance commands were functions only of time.
First stage cutoff and stage separation were commanded when the IU received a signal that the tank's fuel level had reached a predetermined point. Guidance during the second and third stage burns depended both on time and navigation measurements, in order to achieve the target orbit using the minimum fuel.
Second stage engine cutoff was commanded by the IU at a pre-determined fuel level, and the stage was separated. By this time, the vehicle had reached its approximate orbital altitude, and the third stage burn was just long enough to reach a circular parking orbit
Parking orbit
A parking orbit is a temporary orbit used during the launch of a satellite or other space probe. A launch vehicle boosts into the parking orbit, then coasts for a while, then fires again to enter the final desired trajectory...
.
During manned Apollo missions, the vehicle coasted in Earth orbit for 2-4 passes as the crew performed checks of systems status and other tasks, and as ground stations tracked the vehicle. During the hour and a half after launch, tracking stations around the world had refined estimates of the vehicle's position and velocity, collectively known as its state vector. The latest estimates were relayed to the guidance systems in the IU, and to the Command Module Computer in the spacecraft. When the Moon, Earth, and vehicle were in the optimum geometrical configuration, the third stage was reignited to put the vehicle into a translunar orbit. For Apollo 15, for example, this burn lasted 5 minutes 55 seconds.
After translunar injection came the maneuver called transposition, docking, and extraction. This was under crew control, but the IU held the S-IVB/IU vehicle steady while the Command/Service Module (CSM) first separated from the vehicle, rotated 180 degrees, and returned to dock with the Lunar Module (LM). When the CSM and LM had "hard docked" (connected by a dozen latches), the rearranged spacecraft separated from the S-IVB/IU.
The last function of the IU was to command the very small maneuver necessary to keep the S-IVB/IU out of the way of the spacecraft. On some missions the S-IVB/IU went into high Earth or Solar orbit, while on others it was crashed into the Moon; seismometers were left on the Moon during Apollo 11, 12, 14, 15, and 16, and the S-IVB/IUs of Apollo 13, 14, 15, 16, and 17 were directed to crash. These impacts provided impulses that were recorded by the seismometer network to yield information about the geological structure of the Moon.
Subsystems
Structure
The basic IU structure is a short cylinder, 36 inches high and 260 inches (6,604 mm) in diameter, fabricated of an aluminum alloy honeycomb sandwich material 0.95 inches (24.1 mm) thick. The cylinder is manufactured in three 120-degree segments, which are joined by splice plates into an integral structure. The top and bottom edges are made from extruded aluminum channels bonded to the honeycomb sandwich. This type of construction was selected for its high strength to weight ratio, acoustical insulation, and thermal conductivity properties. The IU supported the components mounted on its inner wall and the weight of the Apollo spacecraft above (the Lunar Module, the Command Module, the Service Module, and the Launch Escape Tower). To facilitate handling the IU before it was assembled into the Saturn, the fore and aft protective rings, 6 inches tall and painted blue, were bolted to the top and bottom channels. These were removed in the course of stacking the IU into the Saturn vehicle.The IU is divided into 24 locations, which are marked on the interior by numbers 1-24 on the aluminum surface just above the blue flange.
Guidance and control
ST-124-M3 inertial platform
The ST-124-M3 is a device for measuring acceleration and attitude of the Saturn V launch vehicle. It was carried by the Saturn V Instrument Unit, a , section of the Saturn V that fit between the third stage and the Apollo spacecraft...
at location 21) measured acceleration and attitude. A launch vehicle digital computer (LVDC at location 19) solved guidance equations, and an analog flight control computer (location 16) issued commands to steer the vehicle.
The attitude of the vehicle was defined in terms of three axes:
- The roll axis (X) runs from tail to nose and was vertical at time of launch.
- The pitch axis (Y) is at right angles to the roll axis, and is marked on the exterior of the IU by +Y above the viewport, outside location 21.
- The yaw axis (Z) is at right angles to both the pitch and roll axis, and is marked by +Z outside location 3.
The ST-124-M3 inertial platform
ST-124-M3 inertial platform
The ST-124-M3 is a device for measuring acceleration and attitude of the Saturn V launch vehicle. It was carried by the Saturn V Instrument Unit, a , section of the Saturn V that fit between the third stage and the Apollo spacecraft...
contains three gimbal
Gimbal
A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain immobile regardless of the motion of its support...
s: the outer gimbal (which can rotate 360° about the roll or X axis of the vehicle), the middle gimbal (which can rotate ±45° about the yaw or Z axis of the vehicle), and the inner or inertial gimbal (which can rotate 360° about the pitch or Y axis of the vehicle). The inner gimbal is a platform to which is fixed several components:
- Two vertical alignment pendulums sent signals before launch to ground support equipment, which generated signals to the platform gyro torque generators to level the inner gimbal. The vertical alignment system levelled the platform to an accuracy of ±2.5 arc seconds.
- Two prismPrism (optics)In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
s, one fixed and one servoServomechanismthumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
-driven, were used with an external theodoliteTheodoliteA theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
which sighted through the viewport outside location 21 to set the azimuth of the inner gimbal before launch. The azimuth could be set to an accuracy of ±5 arc seconds. - Three single-degree-of-freedom gyroscopeGyroscopeA gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
s have their input axes aligned along an orthogonal inertial coordinate system. Three signal generators, fixed to the output axis of each gyro, generated electrical signals proportional to the torqueTorqueTorque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
disturbances. The signals were transmitted through the servo electronics which terminated in the gimbal pivot servotorque motors. The servoloops maintained the inner gimbal rotationally fixed in inertial space. That is, while the vehicle rolled, pitched, and yawed, the inner gimbal remained in the same attitude to which it was set just before launch. Though it was being translated during the launch and orbit process, it was rotationally fixed. - Three integrating accelerometerAccelerometerAn accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
s measured the three components of velocity resulting from vehicle propulsion. The accelerometer measurements were sent through the launch vehicle data adapter (LDVA at location 19) to the LVDC. In the LVDC the accelerometer measurements were combined with the computed gravitational acceleration to obtain velocity and position of the vehicle.
The angular positions of gimbals on their axes were measured by resolvers, which sent their signals to the LVDA. The LVDA was the input/output device for the LVDC. It performed the necessary processing of signals to make these signals acceptable to the LVDC.
The instantaneous attitude of the vehicle was compared with the desired vehicle attitude in the LVDC. Attitude correction signals from the LVDC were converted into control commands by the flight control computer. The required thrust direction was obtained by gimbaling the engines in the propelling stage to change the thrust direction of the vehicle. Gimbaling of these engines was accomplished through hydraulic actuator
Actuator
An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...
s. In the first and second stages (S-IC and S-II), the four outboard engines were gimbaled to control roll, pitch, and yaw. Since the third (S-IVB) stage has only one engine, an auxiliary propulsion system was used for roll control during powered flight. The auxiliary propulsion system provides complete attitude control during coast flight of the S-IUB/IU stage.
Environmental control
The environmental control system (ECS) maintains an acceptable operating environment for the IU equipment during preflight and flight operations. The ECS is composed of the following:- The thermal conditioning system (TCS), which maintains a circulating coolant temperature to the electronic equipment of 59° ± 1°F (15 ± 5/9 °C).
- Preflight purging system, which maintains a supply of temperature- and pressure-regulated mixture of air and gaseous nitrogen (air/GN2) in the IU/S-IVB equipment area.
- Gas bearing supply system, which furnishes GN2 to the ST-124-M3 inertial platform gas bearings.
- Hazardous gas detection sampling equipment which monitors the IU/S-IVB forward interstage area for the presence of hazardous vapors
Thermal conditioning
Thermal conditioning panels, also called cold plates, were located in both the IU and S-IVB stage (up to sixteen in each stage). Each cold plate contains tapped bolt holes in a grid pattern which provides flexibility of component mounting.The cooling fluid circulated through the TCS was a mixture of 60 percent methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
and 40 percent demineralized water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
by weight. Each cold plate was capable of dissipating at least 420 watts.
During flight, heat generated by equipment mounted on the cold plates was dissipated to space by a sublimation heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
. Water from a reservoir (water accumulator) was exposed to the low temperature and pressure environment of space, where it first freezes and then sublimates, taking heat from the heat exchanger and transferring it to the water molecules which escape to space in gaseous state. Water/methanol was cooled by circulation through the heat exchanger.
Preflight air/GN2 purge system
Before flight, ground support equipment (GSE) supplies cooled, filtered ventilating air to the IU, entering via the large duct in the middle of the umbilical panel (location 7), and branching into two ducts at the top that are carried around the IU in the cable rack. Downward pointing vents from these ducts release ventilating air to the interior of the IU. During fueling, gaseous nitrogen was supplied instead of air, to purge any propellant gases that might otherwise accumulate in the IU.Gas bearing supply
To reduce errors in sensing attitude and velocity, designers cut friction to a minimum in the platform gyros and accelerometers by floating the bearings on a thin film of dry nitrogen. The nitrogen was supplied from a sphere holding 2 cu ft (56.6 l) of gas at 3,000 psig (pounds per square inch gauge, i.e. psi above one atmosphere) (20,7 MPaMPA
-Academic degrees:* Master of Professional Accountancy* Master of Public Administration* Master of Public Affairs* Master of Physician's Assistant-Chemicals:* Medroxyprogesterone acetate, also known by the brand name Depo-Provera* Morpholide of pelargonic acid...
). This sphere is 21 inches (0,53 m) in diameter and is mounted at location 22, to the left of the ST-124-M3. Gas from the supply sphere passes through a filter, a pressure regulator, and a heat exchanger before flowing through the bearings in the stable platform.
Hazardous gas detection
The hazardous gas detection system monitors the presence of hazardous gases in the IU and S-IVB stage forward compartments during vehicle fueling. Gas was sampledSampling (statistics)
In statistics and survey methodology, sampling is concerned with the selection of a subset of individuals from within a population to estimate characteristics of the whole population....
at four locations: between panels 1 and 2, 7 and 8, 13 and 14, and 19 and 20. Tubes lead from these locations to location 7, where they were connected to ground support equipment (external to the IU) which can detect hazardous gases.
Emergency detection
The emergency detection system (EDS) sensed initial development of conditions in the flight vehicle during the boost phases of flight which could cause vehicle failure. The EDS reacted to these emergency situations in one of two ways. If breakup of the vehicle were imminent, an automatic abort sequence would be initiated. If, however, the emergency condition were developing slowly enough or were of such a nature that the flight crew can evaluate it and take action, only visual indications were provided to the flight crew. Once an abort sequence had been initiated, either automatically or manually, it was irrevocable and ran to completion.The EDS was distributed throughout the vehicle and includes some components in the IU. There were nine EDS rate gyros installed at location 15 in the IU. Three gyros monitored each of the three axes (pitch, roll and yaw), providing triple redundancy. The control signal processor (location 15) provided power to and received inputs from the nine EDS rate gyros. These inputs were processed and sent to the EDS distributor (location 14) and to the flight control computer (location 16). The EDS distributor served as a junction box and switching device to furnish the spacecraft display panels with emergency signals if emergency conditions existed. It also contained relay and diode logic for the automatic abort sequence. An electronic timer (location 17) was activated at liftoff and 30 seconds later energized relays in the EDS distributor which allowed multiple engine shutdown. This function was inhibited during the first 30 seconds of launch, to preclude the vehicle falling back into the launch area. While the automatic abort was inhibited, the flight crew can initiate a manual abort if an angular-overrate or two-engine-out condition arose.
Radio communications
The IU communicated by radio continually to ground for several purposes. The measurement and telemetry system communicated data about internal processes and conditions on the Saturn V. The tracking system communicated data used by the Mission Ground Station (MGS) to determine vehicle location. The radio command system allowed the MGS to send commands up to the IU.Measuring and telemetry
Approximately 200 parameters were measured on the IU and transmitted to the ground, in order to- Assist in the checkout of the launch vehicle prior to launch,
- Determine vehicle condition and to verify received commands during flight, and
- Facilitate postflight analysis of the mission.
Parameters measured include acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
, angular velocity
Angular velocity
In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...
, flow rate, position, pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
, temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
, frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, and others. Sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
signals were conditioned by amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
s or converter
Converter
-Electromagnetics:*Frequency converter*"voltage converter", another name for**electromagnetic transformer**switched-mode power supply**DC to DC converter-Electronics:*Digital-to-analog converter*Analog-to-digital converter...
s located in measuring racks. There are four measuring racks in the IU at locations 1, 9, and 15 and twenty signal conditioning modules in each. Conditioned signals were routed to their assigned telemetry channel by the measuring distributor at location 10. There were two telemetry links. In order for the two IU telemetry links to handle approximately 200 separate measurements, these links must be shared. Both frequency sharing and time sharing multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
techniques were used to accomplish this. The two modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
techniques used were pulse code modulation/frequency modulation (PCM/FM) and frequency modulation/frequency modulation (FM/FM).
Two Model 270 time sharing multiplexer
Multiplexer
In electronics, a multiplexer is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output...
s (MUX-270) were used in the IU telemetry system, mounted at locations 9 and 10. Each one operates as a 30x120 multiplexer (30 primary channels, each sampled 120 times per second) with provisions for submultiplexing individual primary channels to form 10 subchannels each sampled at 12 times per second. Outputs from the MUX-270 go to the PCM/DDAS assembly model 301 at location 12, which in turn drives the 245.3 MHz PCM VHF transmitter.
The FM/FM signals were carried in 28 subcarrier channels and transmitted by a 250.7 MHz FM transmitter.
Both the FM/FM and the PCM/FM channels were coupled to the two telemetry antennas on opposite sides of the IU outside locations 10 and 22.
Tracking
C-band radarRadar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
transponder
Transponder
In telecommunication, the term transponder has the following meanings:...
s carried by the IU provided tracking data to the ground which were used to determine the vehicle's trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
. The transponder received coded or single pulse interrogation from ground stations and transmitted a single-pulse reply in the same frequency band (5.4 to 5.9 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
). A common antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
was used for receiving and transmitting, The C-band transponder antennas are outside locations 11 and 23, immediately below CCS PCM omni receive antennas.
Radio command
The command communications system (CCS) provided for digital data transmission from ground stations to the LVDC. This communications link was used to update guidance information or command certain other functions through the LVDC. Command data originated in the Mission Control CenterMission Control Center
A mission control center is an entity that manages aerospace vehicle flights, usually from the point of lift-off until the landing or the end of the mission. A staff of flight controllers and other support personnel monitor all aspects of the mission using telemetry, and send commands to the...
, Houston, and was sent to remote stations for transmission to the launch vehicle. Command messages were transmitted from the ground at 2101.8 MHz. The received message was passed to the command decoder
Decoder
A decoder is a device which does the reverse operation of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode...
(location 18), where it was checked for authenticity before being passed to the LVDC. Verification of message receipt was accomplished through the IU PCM telemetry system. The CCS system used five antennas:
- A single directional antenna outside location 3-4,
- Two omni transmit antennas outside locations 11 and 23, and
- Two omni receive antennas outside locations 12 and 24.
Power
Power during flight originated with four silver-zinc batteries with a nominal voltage of 28±2 vdc. Battery D10 sat on a shelf at location 5, batteries D30 and D40 were on shelves in location 4, and battery D20 was at location 24. Two power supplies converted the unregulated battery power to regulated 56 vdc and 5 vdc. The 56 vdc power supply was at location 1 and provided power to the ST-124-M3 platform electronic assembly and the accelerometer signal conditioner. The 5 vdc power supply at location 12 provided 5 ±.005 vdc to the IU measuring system.Gallery
These images show the development of the IU. The first four Saturn launches did not have an IU, but used guidance, telemetry and other equipment installed on top of the first stage.The first IU flew on the fifth Saturn launch, SA-5, and was 12 in 10 in (3.91 m) in diameter and 4 in 10 in (1.47 m) high. The components it carried were in pressurized containers. This version flew on SA-5, SA-6 and SA-7. The IU carried by missions SA-8, -9, and -10 was only 2 in 10 in (0.8636 m) high, and was not pressurized.
With the Saturn IB and Saturn V launches, a third version was used, 21.6 feet (6.6 m) in diameter and 3 foot (0.9144 m) high. Comparison of these photographs of the Instrument Unit shows that the configuration of components carried by this version changed, depending on the mission. Some equipment was deleted (e.g. the Azusa tracking system was deleted from later IUs), some equipment was added (e.g. a fourth battery for longer missions), and other components were moved around.
These images also show that some components (e.g. batteries, the ST-124 inertial platform) were installed in the IU after it had been stacked in the VAB on top of the S-IVB third stage.
Saturn
- Bilstein, Roger E. (1980). Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles. NASA SP-4206. ISBN 0-16-048909-1. Available on-line: HTML or PDF
- David S. Akens. ‘’Saturn Illustrated Chronology. Saturn's First Eleven Years: April 1957 through April 1968’’. NASA - Marshall Space Flight Center, MHR-5, 20 Jan 1971. Available online: HTML
- “Saturn I Summary.” An 43-page popular account of the Saturn I program, dated 15 February 1966, covering missions SA-1 to SA-10. Available online from NTRS: PDF
- "Saturn V Press Kit." Includes documents on Saturn V, first stage, F-1 engine, second stage, J-2 engine, Instrument Unit, facilities, testing, vehicle assembly and launch, program manager, flight history, STS-1, contractors, glossary, and index. Available online: HTML
- "The Apollo "A"/Saturn C-1 Launch Vehicle System". NASA MSFC Saturn Systems Office, 17 July 1961. 410 pages. NASA TM X-69174. MOR-MSAT- 61-5. Available online: PDF Information and drawings about version 1 of the IU.
- Duran, B.E. "Saturn I/IB Launch Vehicle Operational Status and Experience". Paper given at Aeronautic and Space Engineering and Manufacturing Meeting of the Society of Automotive Engineers, Los Angeles, CA, Oct 7-11, 1968. 30 pages. Duran worked for Chrysler, maker of the S-1 booster.
- "Steps to Saturn". NASA MSFC, 106 pages. Available online:PDF Describes booster manufacture by MSFC and use of canisters containing guidance equipment before the IU.
Apollo
- Charles D. Benson and William Barnaby Faherty. Moonport: A History of Apollo Launch Facilities and Operations. NASA SP-4204, 1978. Available online: HTML
- "Apollo Program Summary Report." NASA Lyndon B. Johnson Space Center, Houston, Texas, April 1975. JSC-09423. Available online: PDF
- Ivan D. Ertel, Mary Louise Mors, Jean Kernahan Bays, Courtney G. Brooks and Roland W. Newkirk. The Apollo Spacecraft: A Chronology. NASA SP-4009. Available online: HTML
- Orloff, Richard W. "Apollo By The Numbers". NASA History Division, Washington, DC, 2000. NASA SP-2000-4029. 345 pages. Available online: HTML Appendices useful.
- "Apollo Program Flight Summary Report Apollo Missions AS-201 through Apollo 16". NASA Office of Manned Space Flight, Une 1972. 125 pages. Available online: PDF
Specific missions
- "Saturn SA-1 Flight Evaluation". NASA MSFC, December 14, 1961. MPRSAT- WF-61-8. Available online:PDF Describes the Saturn guidance system before the IU.
- Brandner, F.W. "Technical Information Summary Concerning Saturn Vehicle SA-2". NASA MSFC Memo dated 5 April 1962. TMX 51831. 16 pages. Available online: PDF Describes the Saturn guidance system before the IU.
- "Results of the Fourth Saturn IB Launch Vehicle Test Flight AS-204". NASA MSFC, 5 April 1968. 365 pages. MPR-SAT-FE-68-2. NASA TM X-61111. Available online: PDF Describes changes to the IU made on the basis of data from mission SA-204.
- Chrysler Corporation, Huntsville Division. "Saturn Antenna Systems, SA-5". NASA MSFC Astrionics Division Instrumentation Branch, 18 June 1963. 439 pages. Available online: PDF Describes some aspects of version 1 of the IU.
- Weichel, H.J. "SA-8 Flight Test Data Report". NASA Technical Memorandum TM X-53308. 2 August 1965. Available online:PDF According to this, the ASC-15 and the ST-90 were used in the active guidance system, while the ST-124 was part of the passenger system.
- “Saturn V Flight Manual SA-507.” A 244-page description of Saturn-Apollo 507, dated 5 October 1969. Includes a chapter about the instrument unit (Section VII, PDF page 149). Available on-line: PDF
Instrument Unit
- IBM. "Instrument Unit System Description and Component Data." This lists, in Table 1, all components by name, part number, reference designation and location for IU-201 to -212 and IU-501 to -515. It also includes photos of many components. The change history page lists six changes, the latest being January 1970, the year IU-508 was launched.
- “Instrument Unit Fact Sheet.” An 8-page Saturn V News Reference, dated December 1968, about the time IU-505 was delivered to Cape Canaveral. Available online: PDF
- “Saturn Instrument Unit.” A 102-page description of the IU, dated April 1968, prepared by Boeing.
- “Astrionics System Handbook for Saturn Launch Vehicles.” A 417-page description of most of the functions and subsystems of the instrument unit, dated 1 November 1968. Available on-line: PDF
- Lowery, H.R. "Saturn Instrument Unit Command System". NASA MSFC Huntsville, Alabama, 22 October 1965. 45 pages. Technical Memorandum X- 53350. Available online:PDF
- "Saturn IB/V Instrument Unit Instrumentation System Description". International Business Machines, Federal Systems Division, Huntsville, Alabama, 1 June 1966. 119 pages. IBM No. 65-966-0021, MSFC No. III-5-509-1. Available online:PDF Describes the transducers, measurement system, and telemetry function of the IU.
Instrument Unit Guidance
- Herman E. Thomason. “General Description of the ST-124M Inertial Platform System.” NASA TN D-2983, dated September 1965. 93 pages. This has clearer figures than most of the PDF documents about the IU, providing the best views of the insides of the gyros and gas bearings. Available on-line: PDF
- Walter HaeussermannWalter HaeussermannWalter Haeussermann was a German-American aerospace engineer and member of the "von Braun rocket group", both at Peenemünde and later at Marshall Space Flight Center, where he was the director of the guidance and control laboratory...
. “Description and Performance of the Saturn Launch Vehicle's Navigation, Guidance, and Control System.” NASA TN D-5869, dated July 1970. 52 pages. Available online: PDF - Richard L. Moore and Herman E. Thomason. “Gimbal Geometry and Attitude Sensing of the ST-124 Stabilized Platform.” NASA TN D-1118, dated May 1962. An early, and mathematical, rather than descriptive, account of the ST-124. At this date the ST-124 was a 4-gimbal concept, whereas the version that flew had only 3 gimbals. Available online:PDF
- "Saturn V Launch Vehicle Digital Computer. Volume 1: General Description and Theory." IBM, 30 November 1964. Changed 4 January 1965. 256 pages. Available online: PDF
- “Laboratory Maintenance Instructions for the Saturn V Launch Vehicle Digital Computer.” Volume 1 of 2, dated 4 January 1965. 256 pages.
- Decher, Rudolf. "The Astrionics System of Saturn Launch Vehicles". NASA MSFC Huntsville, Alabama, 1 February 1966. 180 pages. NASA TM X- 53384. Available online: PDF
- Lyons, R.E. and Vanderkulk, W. "The Use of Triple-Modular Redundancy to Improve Computer Reliability". IBM Journal, April 1962, pp. 200–209. Available online: PDF Theory behind the LVDC.
- Stumpf, David K. "Titan II. A History of a Cold War Missile Program.". University of Arkansas Press, Fayetteville, Arkansas, 2000. ISBN 1-55728-601-9. Picture of the ASC-15 computer used on the Titan II and on early Saturn flights. The ASC-15 was the predecessor of the LVDC, and was the guidance computer before the IU and on IU version 1, at least.
NASA computers
- Tomayko, James E. "Computers in Spaceflight: The NASA Experience". NASA Contractor Report 182505, March 1988. Available online: HTML
- "Spaceborne Digital Computer Systems". NASA, SP-8070, March 1971. Available online: PDF
External links
- Space Launch Report, Saturn Vehicle History by Ed Kyle (HTMLF)
- Project Apollo Drawings and Technical Diagrams HTML
- Project Apollo Archive, Apollo Image Gallery, NASA Public Affairs Office website by Kip Teague HTML
- Apollo Lunar Surface Journal HTML
- QuickTime Virtual Reality movie of the interior of IU-514 on display at National Air and Space Museum, Udvar-Hazy Center, Dulles, Virginia MOV The names of internal components appear in the lower left part of the frame when you mouse over them.