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 For the sun position in the 7°–20 range at lunar landing, the transposition and docking operations will be in daylight, as shown in Figure 25. The reorientation maneuver will be such that the sun is incident on the LM docking tunnel for best visibility. The maneuver then is such that the vehicle is pitched through about 60 degrees. At this point, both the spacecraft and launch vehicle are communicating over their S-band omni antennas which, in fact, have a 30° to 40° null zone in both front and back. In a short time, however (about 15 minutes after injection), S-IVB communications will be switched automatically from the omni antennas to directional antennas; this switchover to the directional antenna must be taken into consideration in the selection of the reorientation maneuver. Therefore, following the 60° pitch, there must be approximately a 180° roll maneuver to place the launch vehicle directional antenna in the proper position for transmission when the switchover is made. Actually, the pitch and roll maneuver will be done simulta­neously, subject to the gimbal lock considerations. As discussed in the earth orbit phase, these maneuvers are performed at low rates in order not to require an excessive amount of S-IVB RCS propellant.

During this period of reorientation the earth will have acquired the vehicle and tracking will have been continuous except for a brief period during the 60° pitch maneuver when the omni antenna null zone swept through the ground station. A tracking period of about 10 minutes will be required for the ground to accurately determine the vehicle's orbit, and to provide a "go" decision for transposition and docking to proceed.

Having received the decision to proceed with transposition and docking, the Command and Service Modules separate from the S-IVB/LM combination using the SM RCS System. This separation severs the hardline control interface between the crew and the S-IVB; any further maneuvers of the S-IVB will need to come from the ground command. However, the orientation selected before separation was one which will not require any adjustments—at least for the first hour, during which transposition and docking will normally be completed. Present plans are to place the vehicle in an inertial attitude hold mode before separation, oriented so that the launch vehicle direc­tional antenna continues to see the ground station as the spacecraft trajectory sweeps through about 45 degrees of central angle during the next 45 minutes. During this period the S-IVB directional antenna has been switched to its narrow beam, but communications are maintained. During the second hour of the transposition and docking phase, which is provided for contingencies, it may be nec­essary to reorient the S-IVB (from the ground) to maintain communi­cations with the launch vehicle.