See list belowAPR 30 196868-PA-T-89PA/Chief, Apollo Data Priority CoordinationCSM should have good rendezvous navigation in the lunar mission
1. As you know, I have been pushing to get the capability back into the command module computer program to compute CSI and CDH rendezvous maneuver targeting. The reason I consider this valuable is that with both VHF ranging and sextant data, the command module potentially has a better rendezvous guidance system than the LM. Thus, with that capability, it could provide the comparison “yard stick” for evaluating the LM PGNCS determined maneuvers during a nominal flight and could provide targeting for its own maneuvers if a command module rescue situation arises.
2. I submitted a PCR for Colossus and MIT responded with a six week program delivery schedule slip which, of course, is unacceptable. Therefore, this PCR has been added to the list of changes to be con- sidered for later versions of Colossus. During our discussion of this PCR, someone remarked that the VHF ranging device is limited to use for ranges less than 200 nautical miles, and that lighting conditions for sextant observation were poor prior to the CSI and CDH maneuvers. If this were true, it would substantially reduce the benefit of this capability, and in fact, might make it impossible see the command module as noted above. I have checked into the actual situation for lunar rendezvous and have found quite the opposite. The tracking conditions are really very good. Attached to this memorandum are figures which show this. They were lifted from an excellent memorandum (68-FM64-17) written by a couple of Ed Lineberry's people – James D. Alexander and Francisco J. T. Leon-Guerrero. You will observe (Figure 1) that approximately five minutes after insertion into orbit both spacecraft are in darkness which should make sextant tracking ideal and in fact at no time after that and prior to TPI is the angle between the LM and the sun as observed from the command module less than 70°. Furthermore, you will note (Figure 2) that, even if 200 nautical miles is a hard constraint on VHF ranging, it should be possible to get between 5 and 10 minutes worth of tracking before CSI, which should do quite a bit of good. And, or course, as Ed Lineberry says, there is nothing sacred about doing CSI than soon. That is, by delaying it 5 or 10 minutes, we could obtain an equal amount of extra VHF tracking. Of course, hopefully, VHF will work at ranges greater than 200 miles, particularly, if we are willing to restrict voice communications. (Figures 3 and 4 are attached to show an equally good situation will exist on the “F” mission.)
3. My basic purpose in sending around this memorandum is to clarify the situation by distributing this data, which I found very interesting, and to reemphasize the desirability of equipping and utilizing the CSM in this way.