Simplification to the pre-PDI abort procedure

See list attachedMarch 12, 196969-PA-T-45APA/Chief, Apollo Data Priority CoordinationSimplification to the pre-PDI abort procedure

As a result of a passing comment in one of my previous notes, Tommy Gibson and George Cherry looked into what it would take to provide automatic PGNCS targeting for LM aborts at initiation of powered descent (PDI). They found the capability already exists in the LUMINARY program. How's that for great!

The situation I am discussing is when the need for abort is recognized after DOI and before PDI on a lunar landing mission. The ideal proce- dure, of course, is for the LM to make a maneuver at about PDI time which will set up a nominal rendezvous sequence with CSI ½ rev later. This is exactly what the DPS and APS abort programs (P70 and P71) do automatically, but it was thought these programs could only be used if powered descent was actually started and we certainly didn't want to start powered descent – a retrograde maneuver when the abort maneuver must be posigrade. That would make it necessary to execute a large attitude change while thrusting. It turns out that the crew may obtain automatic targeting for an abort maneuver by proceeding into the descent program (P63) just as if intending to land, except that he must maneuver the spacecraft manually into the posigrade abort direction prior to PDI time. He actually starts the DPS burn in P63 but since P63 does not start descent guidance until the engine is throttled up, it will auto- matically maintain the abort attitude the crew has established. After achieving engine stability at about TIG plus five seconds, the crew can press the Abort button which will automatically call up the DPS Abort program (P70) to compute the abort maneuver targets, immediately throttle up to full thrust, and control the burn.

This certainly seems like a straightforward procedure, completely con- sistent with standard descent procedures, and aborts immediately after PDI. I think we should establish this as our primary abort technique for this mission period.

Great work, Tom and George. Keep that up and I predict you'll go places.