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Jun 16, 2012

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.

The LM flight control system was built in phases so that additional higher level systems and functions were added afterwards to the base system. So the basic systems served as a backup for the high level functions if they failed. In LM you can find 3 or 4 levels to control the flight. At the base level you had direct controls to open or close the RCS (Reaction Control Subsystem) valves and maybe some analog electronics for some basic functions or controls. Then you had the AGS, which was alone able to fly the LM and keep it level since it had its own simple IMU and electronic computer. And finally there was the top most PGNS (Primary Guidance and Navigation Section) which used the LGC to calculate more complex trajectories and controls. All levels could be used and switched on and off as required in the LM cabin (or cockpit) by the pilots. Here is an early illustration of the lunar landing phase.

Commander on left and LM pilot on the right controlling the Lunar Module

When flying the LM manually or semimanually the pilot controlled the attitude using the right hand controller (joystick) and the thrust or translation using the left hand controller. The left stick was called TTCA (Thrust / Translation Controller Assembly) and the right joystick ACA (Attitude Controller Assembly). Those controllers were doubled, each pilot had his own.

The following picture gives more detailed information about the controls and displays there was available to the astronauts.

LM controls and displays

The equipment used to steer the vehicle were:

handcontrollers TTCAs and ACAs in CDS
CDS - Controls (and Displays) Subsystem
IMUs - Inertial Measurement Units (2)
AOT - Alingment Optical Telescope
LR Landing Radar (Radar Subsystem)
RR Rendezvous Radar (Radar Subsystem)


LGC - LM Guidance Computer or Apollo Guidance Computer (AGC)
AGS - Abort Guidance Section (Part of GN&CS [Guidance, Navigation & Control Subsystem])
CES - Control Electronics Section (Analog electronics in GN&CS)
CDS - Controls and Displays Subsystem

LMDE Descent Engine (Lunar Module Descent Engine made by TRW)
LMAE Ascent Engine
RCS Reaction Control Thrusters (RCS Thrust Chamber Assembly Clusters) (attitude control)
CDS - (Controls and) Displays Subsystem

As known the LM was made of two part (descent and ascent stage). The descent engine was able to vary its thrust but the ascent engine was on/off type. Reaction control thrusters controlled the attitude in all stages.

LM structure and thermal shielding

The reason why the LM looked so crappy was the outer thermal shielding.

LM thermal shielding

Internally LM was a full and tight airplane with pressurized cabin made by Grumman. Fuel tanks were placed outside the pressurized cabin but under the thermal shielding.

LM Internals Parts

More detailed parts list of LM

When the LM thermal shielding is removed the LM looks like an ordinary aircraft which is made inside out. Grumman used lot of ordinary aircraft manufacturing methods and most of the internal structures were made of aluminium.

LM ascent stage without thermal shielding

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