MODULE MISSION DESCRIPTION
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.
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
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
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.
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.
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).
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,
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
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