Upthread: “D” Rendezvous (Jul 25, 1968)
Downthread: D Rendezvous Ground Rules and Working Agreements update (Sep 23, 1968)
See list attachedSeptember 12, 196868-PA-T-197APA/Chief, Apollo Data Priority CoordinationD Rendezvous Mission Techniques Meeting – September 9, 1968
On September 9, we had another D Rendezvous Mission Techniques meeting. Basically what we did there was to discuss the new, simplified rendezvous mission plan and its effect on the work we have done so far. Based on this discussion, I am revising the ground rules and working agreements and will send them out within a week or so. I think we were all quite pleased to find that the changes were relatively minor and for the most part made things simpler – as they should. The two biggest unresolved areas deal with selection of the nominal TPI time and the rendezvous navigation tracking schedule as influenced by the rendezvous radar thermal constraints. I'll discuss these two things in little more detail in this memo.
Flight Crew Support Division has done some excellent work defining the terminal phase lighting constraints. For a LM rendezvous from below, command module from above situation the TPI time window pro- viding acceptable lighting is only about four minutes long. That is, the TPI maneuver should occur within that small time period. It is almost inconceivable, we can expect to hit such a short window even with reasonable system dispersions. Therefore, we have asked Milt Contella's people to re-examine this situation, particularly taking into account the influence of the sun being located out of the orbital plane in an attempt to widen the window as much as possible. We also requested that its boundaries be “hard,” that is mandatory as opposed to merely desirable lighting constraints. In parallel with this, we have asked MPAD to determine the sort of dispersion we can expect to have in TPI time based on the new mission plan and the latest spacecraft systems performance estimates. When this information is available, we will select the nominal TPI time. This choice must be made quite soon because it influences the Operational Trajectory and many other associated things. (If the VBF ranging device is added to the D mission command module, the situation could be relaxed considerably. That would certainly increase the command module rescue capability by a substantial amount.)
The Rendezvous Navigation Mission Techniques panel we set up last time reported the results of their work. They were quite successful, I think, in establishing a set of procedures for W-matrix reinitialization inde- pendent of where they are in the timeline. Unfortunately, the tracking schedule they developed has proven to be unacceptable from a rendezvous radar thermal standpoint, at least for the old double-bubble rendezvous.
An RCA man was at our meeting and gave us an excellent description of the problem. Essentially what it amounts to is that the rendezvous radar thermal protection has been defined (as per specification) to an obsolete lunar landing mission profile. As a result, there is too much insulation on the stability gyro package and shaft motor for a long, earth orbital rendezvous like D. What actually happens is that the fluid in the gyro expands until the expansion bellows burst. After that there is no control of antenna position making it impossible to obtain radar observations of the command module. The new mission profile will probably be marginally acceptable but it involves a lot of turning on and off the rendezvous radar by the crew. This seems like a rather serious problem that could be fixed quite easily. That is, reduce the amount of insulation. Since the meeting, I have contacted Aaron Cohen, who is now getting his people looking into this. It seems to me that the insulation should be designed specifically for the D mission radar. Without the radar the situation becomes extremely serious – no data into the LM at all. And the CSM has a pretty lousy rendezvous guidance system unless the VHF is added.