APS and DPS operational constraints clarification is needed

PD/Chief, Systems Operations BranchDecember 13, 196868-PA-T-274APA/Chief, Apollo Data Priority CoordinationAPS and DPS operational constraints clarification is needed

Procedures for descent abort (and nominal ascent, too) can be made significantly simpler if we assume it is possible to operate the DPS and APS engines to propellant depletion. You have indicated this is an acceptable way to operate the engines both verbally and in writing, and mission techniques have been developed based on that. This memo is to request that the official Operational Data Book be updated to reflect this constraint – or really lack-of-constraint.

Another characteristic of the DPS which should be clarified in the Data Book is the real throttle up constraint. Currently it shows a require- ment for at least 15 seconds operating at 10 percent thrust prior to throttle up to provide sufficient time for trimming the gimbals. As I understand it, engine stability is the only real constraint and that takes much less than 15 seconds. This also has an influence on descent abort procedures since the LM spacecraft computer is now programmed to command full thrust immediately and we'd prefer to operate it that way if this 15 second constraint is not really valid. And we're currently assuming that it's not.

Please call if you have any question and let me know as soon as possible if our assumptions are wrong.