G Rendezvous

See list attachedSEP 12 196868-PA-T-195APA/Chief, Apollo Data Priority CoordinationG Rendezvous

In spite of the feverish activity we have on three swinging missions C, C', and D, a few of us found a couple of minutes to spend on the G Rendezvous. Some things came out of it that are probably worth reporting:

1. As you know, on the D mission during a LM active rendezvous the command module will be targeted with mirror image maneuvers to backup the LM for CSI and CDH. These mirror image maneuvers are identical in magnitude but opposite in direction, since it has been found that the small errors resulting are a reasonable price for the simplicity we obtain in the operation. Unfortunately, when operating around the moon it's apparently not possible to use identical ΔV components for CSM mirror image targeting. This means that it will probably be necessary for the crew to first cycle through the CSI/CDH targeting program for the other spacecraft (P70 series programs) and then run through the targeting for their own spacecraft (P30 series programs).

2. For the D mission it was decided that a single TPI elevation angle could be adopted (27.5°) for all rendezvous situations. That is, either spacecraft coming in from either above or below. Unfortunately, the lunar rendezvous geometry prevents us from adopting this operational simplification and we must use different values of elevation angle depend- ing on whether the approach is from above or below. The values we have selected (based on Jerry Bell's work) are 26.6° for the approach from below and 28.3° for the approach from above. The basic difference between these values is the phase angle between the two vehicles at TPI, which in lunar orbit is much greater than around the earth for the same separation distance. The primary reason for having to use different values is to keep the TPI maneuver along the line-of-sight. Another reason is to keep component maneuver execution time for the two vehicles the same except for differences in their navigation.

If you have any comments or questions about any of this, our next get together on the lunar rendezvous is currently scheduled for 9 a.m. on September 18, 1968.