- Date: Dec 26 1967
- From: PA/Chief, Apollo Data Priority Coordination
- Subject: Lunar lift off shall be planned at discrete times only.
During our December 21 Ascent P[unintelligible] Data Priority meeting we concluded that a continuous launch window for lift off from the lunar surface is not a requirement. That is, all [unintelligible] planning, procedures and program development associated with the nominal lunar landing mission should be based on the assumption that one or more discrete lift off times will be selected for each revolution of the command module and failure to lift off at one of those discrete times will result in a hold to the next discrete time. Each of these lift off times will be selected to produce the nominal differential altitude during the coelliptical rendezvous. If more than one discrete lift off opportunity is provided per command module revolution, it will be obtained by extending the rendezvous operation another revolution with orbital adjustment maneuvers provided to maintain the nominal differential altitude. (Personally, I feel one opportunity each CSM revolution is enough but that’s just my opinion.) At this time, it appears that one additional revolution beyond the rendezvous scheme currently planned would produce two additional discrete windows after the nominal, one occurring 2 1/3 minutes later and the other about 8 minutes after nominal.
If anyone can think of any reason why this constraint is unacceptable, they should let their concern be known immediately. We could not think of any reason except gross emergency which would produce the circumstance wherein having missed a discrete time we would want to go to the earliest possible time as opposed to waiting for the next preselected discrete time. Of course, “anytime” launch capability is being provided throughout the system but only for low probability contingency situations.