Some assumptions about Spacecraft 101 retrofire and reenty procedures

See list belowNOV 27 196767-PA-T-107APA/Chief, Apollo Data Priority CoordinationSome assumptions about Spacecraft 101 retrofire and reenty procedures

1. We have recently held several small Trajectory Control Data Priority Working Group meetings dealing with Spacecraft 101 retrofire and reentry. The results are being documented to show how the various guidance and navigation data sources will be compared to one another and used during the mission. During these discussions a couple of basic assumptions have been made which I thought might be advisable to disseminate.

2. MCC computer programming, procedures and mission rules are being es- tablished based on the assumption that if it is necessary to retrofire and reenter without the G&N either because that system has failed or be- cause there is insufficient time to bring it on line, the retrofire shall be performed SCS auto mode and the reentry shall be ballistic. (Is is assumed that at least two hours and forty minutes, including two periods of darkness, are required for retrofire preparation.) Accordingly, the retrofire time will be computer based on the reentry to be performed by either continuously rolling or by utilizing a 90° bank angle and a time to reverse it.

3. Associated and consistent with this basic assumption is the procedure that if a PGNCS failure is detected at the horizon alignment check per- formed at T_Retro minus 5 minutes and voice communications are available with the ground, a ballistic reentry will be utilized. The compatible retrofire time will have been determined previous to this event and re- layed to the crew, the slip in time being approximately 2 minutes. The obvious objective of this procedure is to reduce landing point disper- sion resulting from a lifting reentry without guidance, and it was felt that with solid ground assistance the delay in retrofire could be accom- plished. Simulated exercises will prove or disprove this.

4. It is assumed that the role of the EMS is solely associated with monitoring and it will not be used directly in control of the spacecraft nor in evaluating performance of other spacecraft systems. There had been some question as to how its roll reference would be initially aligned. It is currently proposed that the nominal reentry bank angle of 55° will be loaded into the EMS and that the spacecraft will be oriented to that bank angle at the time of 0.5 g's when the pilot initializes the EMS. He will then roll to the post-retrofire backup reentry bank angle as deter- mined by MCC and/or onboard charts.