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 CSM/LM SEPARATION

Separation is performed by the LM RCS system (5 seconds burn) about 30 minutes prior to the actual time of LM transfer orbit insertion. The separation delta V is small, about 1 ft/sec.,

so that the two vehicles drift apart very gradually (figure 37). When the vehicles are about 60 feet apart, the LM will pitch up to an attitude which allows the CM crewman visually to inspect (with the sextant) the external portion of the LM including the landing gear and probes.

A few minutes later the vehicles are far enough apart to perform a checkout of the LM rendezvous radar and CSM transponder. Also, during this separated period, the LM platform is fine aligned, the controls and displays are checked out in the LM-alone configuration, and preparations are made for transfer orbit insertion.

Before the LM passed out of line of sight of earth, data transmission and voice communications had been maintained directly using the LM S—band high gain antenna. After losing line of sight, the LM data will be transmitted to the CSM where it is recorded for subsequent playback. This will be the situation during all phases when the LM is behind the moon, since it carries no onboard data recorder of its own.

The separation maneuver was made in such a direction as to place the LM ahead and below the CSM throughout the 30 minutes coast period to the transfer orbit insertion point. This type of separation maneuver avoids the possibility of jet impingement or collision during the transfer burn by increasing the LM/CSM range (for a small delta V) as compared to the forward or rearward separation methods. Another advantage is that it provides clear VHF communications between CSM and LM during the coast and during the transfer maneuver. The two vehicles are about one-quarter mile apart at the time of transfer orbit insertion.

Prior to the engine burn, propellant settling is provided by a five second RCS firing of the four X-axis thrusters.

The insertion maneuver takes place behind the moon about 200° central angle from the landing site (figure 38). Descent engine thrust is maintained at 30% for the first three seconds and is then reduced to 10% for the next 23 seconds and is then increased to 92.5% thrust (9700 lbs.) for the final six seconds of burn.

The period at low thrust is required due to the possibility that the vehicle's center of gravity deviates from its nominal location