Apollo On-board Guidance History (Part 16, Apollo Control Systems)

[This article is based mainly on D.G. Hoag's paper about Apollo's on-board Guidance, Navigation, and Control System history /10/]

APOLLO ON-BOARD GN(et)CS HISTORY /10/

"This account is written from the point of view of one who experienced the hectic but exciting years. An enormous amount of material has been left out for practical reasons, and many worthy names regretfully remain unmentioned. Technical details have been deliberately played down: they can be found in the bibliography. The overall message is simple: In an incredible and audacious task, the landing of men on the moon, the guidance equipment for the mission was created out of primitive principles, prolific imagination, and a lot of hard work." -- Hoag, D.G.

The Beginnings /10/

"The forerunner of the Apollo guidance, navigation, and control system (GNetCS)), is found in an unmanned spacecraft and mission study started in 1957 by the Instrumentation Laboratory at MIT under a contract with the Air Force Ballistic Missile Division.

Milton Trageser (left), Hal Laning and Richard Battin

DSKY Hardware (Part 15, Apollo Control Systems)

[Since it looks like that DSKY is very popular with its companion LGC (or AGC) I add this article to fully cover the DSKY hardware (as it was 1966) in its detail. DSKY was a small and simple terminal device to today's standards. It was used by astronauts to communicate with the primary guidance computer programs. DSKY is interesting since it only had some latching relays to drive the segment displays and some simple transistor type logic to generate keycodes from the keyboard.

Today (2017) this device would be manufactured using maybe a single micro-controller and would be very simple. I am sure that even nowadays many astronauts would like to have a similar device to communicate with the guidance computer at least as a reserve device in case of some problem with the modern touch screens and high resolution displays. Its small size, simplicity and integration with the Apollo software and hardware will keep this device popular in the future also. Most of this material is from /1/. This text and drawings /1/ did have some differences with other documents but is anyway useful in its detail.

The AGC (and DSKY) was designed at the MIT Instrumentation Laboratory under Charles Stark Draper, with hardware design led by Eldon C. Hall. Early architectural work came from J.H. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso, and Hugh Blair-Smith. The flight hardware was fabricated by Raytheon, whose Herb Thaler was also on the architectural team.

Eldon C. Hall

Most of these people can be seen in the following film

YouTube video: "Computer for Apollo, MIT Science Reporter Film"]

Apollo Mission Films (Part 14, Apollo Control Systems)

NASA made several films during the Apollo program about the physics, calculations and programming principles used to do the manned Moon trip. Compared to today's standards many of those are very detailed and give very good information about how the programs behind the successful missions were tailored. Most of films originated from MSC (Manned Spacecraft Center) Houston, Texas. This is a list of links I have found in YouTube (there might be more in various archives).

DSKY Interface (Part 13, Apollo Control Systems)

(DSKY I/O Interface, Apollo Guidance Computer)

[This article describes how the Apollo Guidance Computer (AGC) was connected to the Display and Keyboard Unit (DSKY). This is rather detailed description about the hardware and gives some light about how various devices were connected to the AGC. Since the connection was digital and parallel no special arrangements was required as with the more sensitive analog interfaces. The text is mainly from reference /1/.]

Figure 1. DSKY (Apollo Guidance Computer Display and Keyboard)

Command Module ECS (Part 12, Apollo Control Systems)

Environmental Control System (ECS)

The Apollo environmental control system (ECS) was designed and qualified to support three crewmen for 14 days and to maintain electronic equipment within operating thermal boundaries. The system maintains the pressure atmosphere of 100 percent oxygen and removes trace contaminants and metabolic carbon dioxide by absorption in charcoal and lithium hydroxide beds. (After the Apollo 1 CM accident the launch atmosphere was changed to 60-percent oxygen and 40-percent nitrogen.)

Apollo CM Environmental Control Unit (ECU), a major part of the ECS

[An Apollo Command Module (Block II) Environmental Control Unit (ECU) a major part of the Environmental Control subsystem (ECS), produced by Garrett Corp.'s AiResearch Division, Los Angeles under subcontract to North American Aviation (NAA), prime for the Apollo Command Service Module (CSM) under NASA Contact NAS 9-150. The Environmental Control Unit was the heart of the environmental control subsystem. It is a compact grouping of equipment about 29 inches long, 16 inches deep, and 33 inches at its widest point. It was mounted in the left-hand equipment bay. The unit contains the coolant control panel, water chiller, two water-glycol evaporators, carbon dioxide-odor absorber canisters, and suit heat exchanger, water separator, and compressors.]

CM Command Module (Part 11, Apollo Control Systems)

This article handles the Apollo Command Module. The current NASA command module is called Orion capsule or crew module.

Command Module CM with the Service Module SM connected together with an umbilical (right).  

SM Service Module (Part 10, Apollo Control Systems)

Apollo Service Module (SM) was an important part of the Apollo Command/Service Module (CSM). Nowadays also the new SM which is connected to the Orion capsule is called a service module. Actually Europeans are just now building one (2015).


HISTORY /1/

North American Aviation logo

Apollo Command / Service Module was built by North American Aviation.

James Howard "Dutch" Kindelberger

James Howard "Dutch" Kindelberger was an American aviation pioneer, a leader of North American Aviation in 1934-60.

Apollo Space Suit (Part 9, Apollo Control Systems)

The Apollo space suit was the result of the evolution that took place during the preparation for the Apollo mission during 1960's and before. One could say that the evolution to protect human against low pressure in high altitudes started already when Wiley Post constructed his first pressure suit in 1934.

Wiley Post's 1935 pressure suit

Apollo CM Seats (Couch-Restraint System)

 The hatch could also be opened in space

Lunar Module Control Subsystems (Part 8, Apollo Control Systems)

Lunar Module control system was divide to 12 subsystems. We have already described some of them in our previous parts. Here is now a simplified picture of the LM complete control system and its subsystems.

LM Control System. Many LM subsystems were heavily connected to each other. For example the Instrumentation (IS) collected data from all subsystems. This is sown as C.M.S. (connected to many subsystems).

LEM RCS, Lunar Module Reaction Control Subsystem (Part 7, Apollo Control Systems)

The Reaction Control Subsystem (RCS) consisted of 4 clusters of thrusters (16 all together), fuel feeding system and its control electronics and computers.

Lunar Module (LM) Reaction Control Subsystem (RCS) Thrust Chamber Assembly Clusters (4)

LEM EDS, Lunar Module Explosive Devices Subsystem (Part 6, Apollo Control Systems)

Lunar Module Explosive Devices Subsystem (EDS) and its control was duplicated as most LM systems were.

Lunar Module (LM) EDS devices locations

Heat Transport Section of LM ECS (Part 5, Apollo Control Systems)

Lunar Module ECS (Environmental Control Subsystem) included a section called HTS (Heat Transport Section). Its job was to remove excessive heat from mostly electrical circuits and batteries. It did it by circulating water-glycol through cold plates that were placed under those circuits and sublimated the heat to the space using water sublimators.

Typical cold plate with primary and secondary loop connections

How Astronauts Used the LM (Part 4, Apollo Control Systems)

The space inside the LM was very limited. The crew compartment was about 1 meter long and a round shape with a diameter of about 2 meters. There was additionally some room behind that which was mostly used to store some equipment. The following pictures show how the LM was used for the most important tasks (flying, landing, rendezvous, sleep, exit):

LM Lunar Module (Part 3, Apollo Control Systems)

In LEM or LM there were 2 computers. LM was mostly built by the Grumman Aircraft Engineering company but since MIT was a specialist in IMUs (Inertial Measurement Unit) at that time they got the deal to build the main guidance and navigation section. The main computer was called LGC (LM Guidance Computer) and the secondary computer was in AGS (Abort Guidance Section) which work was to abort the main computer if it had problems.

Apollo Computer in Action (Part 2, Apollo Control Systems)

The LEM (and CSM) computer AGC (Apollo Guidance Computer) was connected to several sensors and controls which it used to get information about the position and situation of the vehicle it controlled.

The following video shows the method to determine the distance of the CSM during the Apollo mission by reading the angle between two known spots in the space. The video shows how to use similar display and keyboard that was used in LEM and CSM. Later in this same video also the method to build the block I AGC is shown in detail. The block I used transistors and the block II computer (the actual computer that was flown to the Moon) used simple intergrated circuitis.

"Computer For Apollo" (1965) - Science Reporter TV Series

The video also shows the "verb - noun" method used to communicate with the AGC. The user could enter verbs and nouns in the pattern "do - something" and the computer then did the requested task and then displayed the results.

The function of the "mark" button is also described. The mark button was used during the actual moon flights.

Some chief designers behind the AGC are also shown in this video: Eldon Hall, Ramon Alonzo and Albert Hopkins.

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LEM Lunar Module (Part 1, Apollo Control Systems)

LEM Lunar Excursion Module, later named LM Lunar Module