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 were not made for some reason. This leaves the LM in a relatively stable situation from which rescue by the CSM could be made, if necessary. However, the planned ascent phase continues with a series of small impulses provided by the LM RCS, and rendezvous occurs with the CSM about two hours after lift-off.

After the LM has docked on the CSM, the LM crew is transferred to the CSM, along with the data and samples collected on the lunar surface. The LM is then jettisoned, and preparations are made for the next major maneuver, transearth injection is slightly less than for lunar orbit insertion, and the propellant expendi­ ture for the SPS is considerably less, about 8000 lbs. since the spacecraft is considerably lighter.

It is of interest to note that up until the LM began its descent operations, a backup for transearth injection was available in the LM descent engine. This is considered a particularly useful capability, since it allows one to guard against an SPS failure during its first major burn for lunar orbit insertion. For this reason, then, the propellant requirement for transearth injection is also shown in terms of what would be required from the LM descent propulsion system, approximately 14, 000 lbs.

Following the transearth injection, the spacecraft is on a plateau much like the outgoing leg of the trajectory to the moon. It is targeted to arrive at safe entry conditions at the proper time to allow it to reach its primary recovery area in the Pacific Ocean. Small midcourse corrections during the transearth coast assure that these conditions are reached. Shortly before arrival at the entry point, the Service Module is jettisoned, and the CM is oriented for entry. Entry range varies between 1500 and 2500 nautical miles and is controlled by rolling the CM during the entry phase. At 25, 000 ft. altitude, the drogue parachutes are deployed and followed a short time later by the main parachutes which slow the CM to safe touchdown conditions.

Recovery is soon effected, and with the CM and crew safe aboard ship, the mission is completed.

Having completed this gross description of the total mission, it will be of interest to devote some attention to a few basic mission planning considerations before proceeding with the more detailed description of the mission.