Final word on the targeting of the externally targeted prethrust spacecraft computer programs

See list belowOCT 30 196767-FM-T-100FM/Deputy ChiefFinal word on the targeting of the externally targeted prethrust spacecraft computer programs

1. This note is to make sure that everyone who needs to know does know how we are actually implementing the general purpose prethrust (targeting) programs in the spacecraft computer programs SUNDANCE, LUMINARY and COLOSSUS. I thought it would probably be worthwhile to pass the word since so many different proposals and tentative decisions have been made before, during and since the GSOP review for those programs.

2. There are two prethrust programs being provided, both of which require targeting from some source external to the spacecraft computer. One of these, P-30, is the External Delta-V program which can be targeted either by cred input via the DSKY or from the ground through the uplink command program, P-27. The targeting consists of the following parameters: time- of-ignition and three complements of delta V in a local horizontal space- craft centered coordinate system.

3. The other program, P-31, may only be targeted from the ground. It is to provide the capability of inputting Lambert targets for a maneuver to be executed (steered) in that mode. There is no capability for the crew to input targeting to this program via the DSKY directly. Of course, it is possible for him to use the rather awkward procedure of going through P-27, if he chooses to do so. The target parameters consist of time-of-ignition, a position vector consisting of three quantities, in and earth or moon centered inertial coordinate system, and the duration of time which it is desired for the spacecraft to consume getting to that position. These are all double precision, octal quantities. Those responsible for RTCC program development please take note, since at one time is had been proposed that some sort of pseudo-External Delta V targeting be used for this program.

4. I would also like to emphasize that it is currently not our intention to eliminate either steering mode—External Delta V nor Lambert. As a matter of fact, it is my understanding that deletion of either one of these modes would save very few, say less than a hundred, words of storage.