- Date: Sep 21 1966
- From: FM1/Deputy Chief, Mission Planning and Analysis Division
- Subject: There are differences in the descent guidance programs on AS-503 and AS-504
It is currently intended to include some sort of tests in the LM descent propulsion and guidance on the AS-503 mission. However, it is not possible to use the same guidance equations on AS-503 as will be used on the AS-504 lunar descent. This is due to obvious differences of an earth orbital mission compared to an actual descent on the moon’s surface. The gravitational potential is different; the objective of the maneuver is different; there is nothing for the lunar landing radar to bounce signals off of, etc. Accordingly it is MIT’s intention, with our concurrence, to omit certain vital parts of the AS-504 descent guidance program from the AS-503 mission. The purpose of this memo is to make sure that you all know this.
It is my understanding that there are four main processors of the AS-504 descent guidance program which are not to be included in the AS-503 program:
- processing of the landing radar data
- landing point designation
- x-axis override
- automatic rate of descent control
In addition, there is likely to be a change in the coordinate system of some sort needed.
I certainly do not claim to be an expert in descent guidance; in fact, quite the opposite. If anything above interests you, I would suggest you contact someone who really knows what they are talking about like Don Cheatham, Floyd Bennett or Tom Price.
Incidentally, we are currently in the midst of an exercise designed to make the AS-278 spacecraft computer programs identical to those for AS-503. Although I don’t expect this to have any influence on the descent guidance, I just mentioned it here to cover that possibility.