GENERAL

A typical mission of the Lunar Module (LM) begins with its separation from the orbiting Command/Service Module (CSM), continues through lunar descent, lunar stay, and lunar ascent, and ends at rendezvous and docking with the orbiting CSM before the return to earth. The LM mission is part of the overall Apollo mission, the objective of which is land two astronauts and scientific equipment on the moon and return them safely to earth.

EARTH VICINITY AND TRANSLUNAR COAST

The Saturn launch vehicle inserts the spacecraft, which is attached to the spacecraft-Lunar Module adapter (SLA),into earth orbit. The LM landing gear is folded and the antennas are stowed while the LM is inside the SLA.

When earth orbit is achieved, the S-IVB stage is shut down and the three astronauts in the Command Module (CM) perform systems status checks and a CSM guidance system reference alignment. Upon completion of earth orbit, the S-IVB engine is restarted to begin trans-lunar injection.

After the initial trans-lunar coasting period, the CSM detaches from the SLA and S-IVB stage, pitches 180 degree, and docks with the LM - a maneuver called transposition and docking. During this maneuver, the LM/S-c stage is stabilized by the S-IVB 
instrumentation unit. After the CSM pulls the LM free, the S-IVB and the SLA are jettisoned and the spacecraft is oriented for continuation of the trans-lunar coast period. During trans-lunar coast, the LM remains passive, except for the inertial measurement unit (IMU) heaters and portions of the Environmental Control Subsystem (ECS) and Electrical Power Subsystem (EPS), which were activated before launch. The CM performs all navigation and guidance functions and, oriented by the Service Module (SM) reaction controls, initiates midcourse correction maneuvers.

LUNAR VICINITY

Approximately 64 hours after launch, the CSM service propulsion system inserts the spacecraft into an elliptical lunar orbit of approximately 60 by 170 nautical miles. While in this orbit, the astronauts perform CSM guidance system reference alignments and orient the spacecraft attitude for a circularization burn at the beginning of the third lunar orbit. At completion of this maneuver, the spacecraft is in a circular orbit 60 nautical miles above the moon. The spacecraft is prepared for a docked CSM/LM descent orbit insertion maneuver (DOI) from the 60 nautical-mile circular orbit. There is no LM activity connected with the descent orbit insertion maneuver.

The descent orbit insertion maneuver, which, when completed, will have placed the spacecraft into an elliptical orbit of approximately 9x 60 nautical miles, is initiated. One-half revolution after initiation of the DOI, the astronauts transfer to the LM to perform activation and checkout procedures. These procedures, which take approximately 4 hours to perform include subsystem activation, IMU alignments, landing gear deployment, and caution/warning checkout. Approximately 2-1/2 revolutions after DOI, the LM undocks and separates from the CSM. Three revolutions after DOI, at approximately 50,000 feet, the CSM returns to the 60 nautical-mile circular orbit; at the same time, the LM begins its descent to the lunar surface.

Descent to the lunar surface consists of three distinct phases: the braking phase from approximately 50,000 to 10,000 feet (high gate), a final approach phase from approximately 10,000 feet to 700 feet (low gate) during which the landing site is observable, and the landing phase, which terminates at touchdown. Descent is performed automatically under control of the Guidance, Navigation, and Control Subsystem (GN&CS) to approximately 700 feet above the lunar surface.

Approximately 2 minutes before reaching the low-gate point, the LM is oriented to begin the final approach phase. During the final approach phase, the LM descends to the low-gate point at nearly constant flight path angle; the attitude is such that the astronauts can observe gross landing area details and manually guide the LM to an alternative landing site, if necessary.

At the low-gate point, the astronauts can select the best landing site and perform the landing phase to touchdown. To accomplish translation to a desired spot on the lunar surface, the thrust vector can be tilted to accelerate the LM in the direction of the landing site. At approximately 3 feet above the lunar surface, the engine is cut off and the vehicle free falls to the lunar surface.

After touchdown on the lunar surface, the two astronauts perform a lunar surface IMU alignment and check all subsystems to determine whether damage occurred upon landing and to assure that all systems can perform the functions required for a successful ascent. The decision is then made whether the nominal planned stay-time operations can be executed. If all the systems check out satisfactorily, the astronauts observe the surrounding lunar landscape, check the LM hatches, and perform a final check of the portable life support system (PLSS) in preparation for one of the astronauts to leave the LM. All equipment not essential for lunar stay is turned off. The astronauts don their PLSS and depressurize the cabin, open the forward hatch, and exit the vehicle to perform the first of four proposed extravehicular activities (EVA's) (LM-10, 11 and 12).

LUNAR STAY

During the first EVA, the astronauts activate the modularized equipment stowage assembly (MESA); unstow and deploy the S-band erectable antenna, if required; remove and use the TV, still, and stereo cameras; set the gnomon on the lunar surface; and collect and stow lunar samples. After approximately 4 hours, the first EVA is terminated.
During the second and subsequent EVA's, many of the original activities are repeated and new ones, such as deploying the advanced lunar experiments package (ALSEP), unstowing and deploying the mobility aid, and performing lunar excursions, are initiated.

Upon termination of the final EVA, the astronauts remove their PLSS and jettison all unnecessary equipment to the lunar surface. The LM is then prepared for launch; subsystems are activated and checked and an IMU alignment is performed. At a predetermined launch time, while tracking the CSM with the rendezvous radar, the ascent engine is ignited. The ascent stage of the LM separates from the descent stage and lifts off the lunar surface.

LIFT-OFF AND TRANSEARTH FLIGHT

During the ascent from the lunar surface to the orbital rendezvous with the CSM, the astronauts perform several maneuvers: concentric sequence initiation (CSI), constant delta. height maneuver (CDH), terminal phase initiation (TPI), and terminal phase finalization (TPF). At approximately 100 feet from the CSM, all Reaction Control Subsystem (RCS) thrusting is terminated and a CSM-active docking maneuver is performed. 

The crew transfers equipment from the LM to the CSM and, after the Commander and the LM Pilot transfer to the CSM, the vehicles are separated and the LM is jettisoned. A brief checkout of the CSM, and determination of transearth thrusting parameters, is followed by the transearth injection maneuver. During the transearth flight, status checks, alignments, and midcourse corrections are performed as required. Approximately 15 minutes before entry into the earth's atmosphere, the SM is jettisoned and the CM is oriented for entry and landing.