Apollo Lunar Module Computer
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Lunar Module Computer
Many people wonder about how people got to the moon in an age before personal computing, and many refuse to believe it was even possible!
I'm collecting together a few facts and figures about the Apollo missions in various webpages, with this one concentrating on the electronic systems of the lunar lander.
I'm collecting together a few facts and figures about the Apollo missions in various webpages, with this one concentrating on the electronic systems of the lunar lander.
AGC
Apollo Guidance Computer
Developed by the MIT Instumentation Laboratory, this was one of the forebears of "mobile computing"! Supercomputers have always been room-filling devices, from their earliest days of code-breaking at Bletchley Park during the war. The requirement for the Lunar Module was obviously for something far smaller and lighter; and one of the ways of achieving this was to create a system built for one purpose only.
Though one of the smallest computers in the world, it still weighed about 70 pounds, was 2 feet long and consumed about 70 watts. It used a combination of technology in the ferrite rope memory and over five thousand integrated circuits, giving 36k of ROM (Read Only Memory) and 2k of RAM (Random Access Memory). With only 2k of space to use for new data during the mission, it's not surprising that the computer could easily become overloaded, as happended during the final stages of Apollo 11's landing approach. It is surprising that they used integrated circuits at all, given the fact that it was such new technology - but reprogramming was essential in flight, and NASA ended up using half the world's supply of intergrated circuits! The memory circuits used magnetic core memory for the erasable part, and high-densiity magnetic rope core memory for the ROM.
Though one of the smallest computers in the world, it still weighed about 70 pounds, was 2 feet long and consumed about 70 watts. It used a combination of technology in the ferrite rope memory and over five thousand integrated circuits, giving 36k of ROM (Read Only Memory) and 2k of RAM (Random Access Memory). With only 2k of space to use for new data during the mission, it's not surprising that the computer could easily become overloaded, as happended during the final stages of Apollo 11's landing approach. It is surprising that they used integrated circuits at all, given the fact that it was such new technology - but reprogramming was essential in flight, and NASA ended up using half the world's supply of intergrated circuits! The memory circuits used magnetic core memory for the erasable part, and high-densiity magnetic rope core memory for the ROM.
Virtual Apollo Guidance Computer
Software is available from here:
http://www.ibiblio.org/apollo/download.html#Downloads
http://www.ibiblio.org/apollo/download.html#Downloads
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PGNCS
Primary Guidance, Navigation and Control System
The Apollo Primary Guidance, Navigation and Control System (PGNCS) (pronounced pings) was a self-contained inertial guidance system that allowed Apollo spacecraft to carry out their missions when communications with Earth were interrupted, either as expected, when the spacecraft were behind the moon, or in case of a communications failure. The Apollo Command Module (CM) and Lunar Module (LM), were each equipped with a version of PGNCS. The PGNCS, and specifically its computer, were also the command center for all system inputs from the LM, including the Alignment Optical Telescope, the radar system, the manual Translation and Rotation device inputs by the astronauts, as well as other inputs from the LM systems.
The CM guidance and navigation system used range data from the very high frequency (VHF) ranging device and angular data from the scanning telescope and from the sextant. The LM primary guidance and navigation system used rendezvous radar tracking data (angles, range, and range rate).
PGNCS was developed by the MIT Instrumentation Laboratory. The Prime Contractor for PGNCS and manufacturer of the Inertial Measurement Unit, IMU was the Delco Division of General Motors. Development was under the direction of Charles Stark Draper and MIT Draper Labs and consisted of the following components:
* an Inertial Measurement Unit (IMU)
* the Apollo Guidance Computer
* resolvers to convert inertial platform angles to signals usable for servo control
* an optical unit
* a mechanical frame, called the Navigation Base (or Navbase), to rigidly connect the optical device and, in the LM, the rendezvous radar to the IMU
* the AGC software
The IMU was gimbaled on three axes. The innermost stable member, a 6 inch beryllium cube, had three gyroscopes and three accelerometers mounted in it. Feedback loops including the resolvers used signals from the gyroscopes to control motors at each axis. This servo system kept the stable member fixed with respect to inertial space. The IMU was derived from the guidance system developed by Draper for the Polaris missile.
Inertial guidance systems are not perfect and Apollo system drifted about one milliradian per hour. Thus it was necessary to "realign" the inertial platform periodically by sighting on stars.
The CM optical system had a fixed sextant, which could measure angles between stars, and Earth or Moon landmarks and planetary horizon. The unit included a scanning telescope for star sightings, and could be used to determine position and orientation in space. In contrast, the LM had an Alignment Optical Telescope, and could only determine the craft's orientation. The outer element of the AOT was a sun-shielded prism that could be rotated to one of three fixed positions relative to the LM, in order to cover a large portion of the lunar sky. When rotated, the AOT's position was readable by the AGC; by pointing the reticule at several different stars, the computer could determine the craft's orientation
The CM guidance and navigation system used range data from the very high frequency (VHF) ranging device and angular data from the scanning telescope and from the sextant. The LM primary guidance and navigation system used rendezvous radar tracking data (angles, range, and range rate).
PGNCS was developed by the MIT Instrumentation Laboratory. The Prime Contractor for PGNCS and manufacturer of the Inertial Measurement Unit, IMU was the Delco Division of General Motors. Development was under the direction of Charles Stark Draper and MIT Draper Labs and consisted of the following components:
* an Inertial Measurement Unit (IMU)
* the Apollo Guidance Computer
* resolvers to convert inertial platform angles to signals usable for servo control
* an optical unit
* a mechanical frame, called the Navigation Base (or Navbase), to rigidly connect the optical device and, in the LM, the rendezvous radar to the IMU
* the AGC software
The IMU was gimbaled on three axes. The innermost stable member, a 6 inch beryllium cube, had three gyroscopes and three accelerometers mounted in it. Feedback loops including the resolvers used signals from the gyroscopes to control motors at each axis. This servo system kept the stable member fixed with respect to inertial space. The IMU was derived from the guidance system developed by Draper for the Polaris missile.
Inertial guidance systems are not perfect and Apollo system drifted about one milliradian per hour. Thus it was necessary to "realign" the inertial platform periodically by sighting on stars.
The CM optical system had a fixed sextant, which could measure angles between stars, and Earth or Moon landmarks and planetary horizon. The unit included a scanning telescope for star sightings, and could be used to determine position and orientation in space. In contrast, the LM had an Alignment Optical Telescope, and could only determine the craft's orientation. The outer element of the AOT was a sun-shielded prism that could be rotated to one of three fixed positions relative to the LM, in order to cover a large portion of the lunar sky. When rotated, the AOT's position was readable by the AGC; by pointing the reticule at several different stars, the computer could determine the craft's orientation
Apollo Lunar Module Alignment Optical Telescope
AGS
Abort Guidance System
The AGS was a computer system used in the LM. It was a completely separate computer system from the LM's AGC, with a different architecture, different instruction-set, and different runtime software. It was in the LM as a kind of backup for the AGC, but was only supposed to be used (as the name implies) in case of an aborted landing. The AGS doesn't have as commanding a rôle in the history of lunar explanation as does the AGC, because no aborts were ever needed in actual missions. However, when the AGS made its few appearances in history it did so dramatically.
Lunar Module Systems
Lunar Module Links
- Apollo 11 and Other Screw-Ups
- historical technical paper
- Apollo Guidance Computer - Wikipedia, the free encyclopedia
- if (wgNotice != '') document.writeln(wgNotice); Apollo Guidance Computer From Wikipedia, the free encyclopedia Jump to: navigation, search This article's citation style may be unclear. The references used may be made clearer with a different or consistent style of citation, footnoting, or extern
- Apollo PGNCS - Wikipedia, the free encyclopedia
- The Apollo Primary Guidance, Navigation and Control System (PGNCS) (pronounced pings) was a self-contained inertial guidance system that allowed Apollo spacecraft to carry out their missions when communications with Earth were interrupted, either as expected, when the spacecraft were behind the moon, or in case of a communications failure.
- The Abort Guidance System
- The AGS was a computer system used in the LM. It was a completely separate computer system from the LM's AGC, with a different architecture, different instruction-set, and different runtime software. It was in the LM as a kind of backup for the AGC, but was only supposed to be used (as the name implies) in case of an aborted landing.
- Computers In Spaceflight
- Computers in Spaceflight: The NASAExperience Part I : Manned Spacecraft Computers Introduction to Part One. - Chapter One - - The Gemini Digital Computer: First Machine in Orbit - The Gemini Digital Computer: First Machine in Orbit. Hardware. Software. Crew interfaces to the Gemini digital
- DSKY Simulator
- With this javascript DSKY you can get a bit of a feeling what it was like to work with the DSKY. The astronauts used this device to communicate with the guidance computer. The crew could ask and pass information to the computer and vice versa. It was sometimes even called 'the third crew member'!
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