Upthread: List of “D/E” Rendezvous open items (Apr 16, 1968)
Downthread: “D” Rendezvous Mission Techniques Task Assignments for MPAD (Jun 20, 1968)
See list belowAPR 23 196868-PA-T-79APA/Chief, Apollo Data Priority CoordinationRendezvous maneuver targeting for guidance system backup
1. During the “D/E” Rendezvous Mission Techniques meeting of April 15, we spent a lot of time discussing the data transmitted from the ground to the spacecraft involving the CSI and CDH maneuvers. This discussion, of course, centered on how the data should be used and led to a tentative conclusion regarding the backup of these LM maneuvers, which is somewhat different than we had previously reached. The purpose of this memorandum is to point out this difference.
2. We had previously concluded that the command module should be prepared to make “mirror image” rendezvous maneuvers in the event of LM problems. We had planned to target the CSM with data obtained by the LM crew from the PGNCS. The failure we had in mind was primarily propulsive. However, when you consider that the problem in the LM could also be in the guidance system, it seemed logical to modify the procedures slightly, since it is no better for the command module to make a bum maneuver than for the LM. Also, it did not seem that we were taking optimum advantage of the LM systems, particularly the AGS. Accordingly, we now propose the following:
Both the AGS and the CSM G&N will be targeting with ground computed CSI/CDH maneuvers passed to the spacecraft in External Delta V coordinates. If for some reason the LM PGNCS computer maneuver is not acceptable, we would class this as a PGNCS failure. Rather than carry out some real time systems analysis at this time critical period, they would switch to the AGS and make the ground related maneuver. If some further problem is encountered prior to the maneuver, the LM would go passive and the command module would continue the countdown and make the ground computed CSI/CDH burn. Following the burn the crew and ground would attempt to ascertain what the problem is in an attempt to get the LM systems ready for the rest of the rendezvous.
This procedure gives two levels of backup (AGS and CSM) to a PGNCS problem and helps keep the LM active. However, operating in this way would likely preclude either input of rendezvous radar data into the AGS or running through its CSI/CDH targeting computations in order to keep it in the best state of readiness to backup the PGNCS. There is still a pocket of resistance (FCSD) to using the AGS in this way which makes some higher level direction necessary. I'll try to get a decision right away, one way or the other.