FM13/Chief, Apollo Trajectory Support OfficeOCT 27 196767-FM-T-98FM/Deputy ChiefLet’s find out if the current MSFN performance is really not good enough for lunar operations.
1. On Monday, October 16, we had a briefing by the Math Physics people on the performance of MSFN tracking the Lunar Orbiter. As you are un- doubtedly aware, orbit determination of that vehicle, once it was put in an Apollo type orbit, became a rather erroneous affair and they have not yet been able to determine what is causing the trouble. The result of the trouble is that the orbital elements produced for a given orbit are said to be substantially different depending on the amount of data processed in the orbit determination.
2. Steps are being taken by Jim McPherson to enlist the aid of the sci- entific community in trying to resolve this problem. It appears they feel their most fruitful line of attach is improvement in the model of the lunar potential. Anticipating that whatever is done may not be entirely satisfactory or may turn out to be as expensive in terms of money, effort and other treasure, we had perhaps better give some thought in another direction. Namely, what is the effect of the orbital ������� of uncertainty we are experiencing now with the MSFN on our signifi- cant onboard sensing and computation capability the most in terms of delta V, crew safety and whatever else you might think of is unacceptable. This can really only be determined by analysis or experiences and it is for this reason that I am putting pen to paper on this occasion.
3. Specifically, I request that you initiate action items, mean or lean, as follows:
a. RAB – Evaluate the effect of current degradation in performance of the MSFN orbit determination capability on lunar orbit rendezvous operations. Some parameters of interest are ������������������� V budget, resultant dispersions in the trajectory and ��������� ellipticity and dispersed differential altitude during ���������� operation, increased dispersion in the maneuver targeting ����� on- board the spacecraft, resultant shift in TPI and ��������������� and the associated change in lighting conditions. And other parameters of that ilk which personnel of RAB themselves are in a much better position to specify.
b. RAB and/or MAB – Evaluate the effect of the degraded MSFN perform- ance we are now experiencing in the determination of spacecraft state vectors on the targeting and execution of the Descent Orbit Insertion (DOI) maneuver. Then determine the impact of that on uncertainty in obtaining the desired landing point and as well as increase in propellant usage which is likely to result from altitude dispersions encountered at initiation of descent braking.
c. MAB – Evaluate the effect of degraded MSFN performance we are now experiencing on ground targeting of the Transearth Injection (TEI) maneuver. Probably the parameter of most interest will be the increase in delta V cost in the midcourse correction maneuvers resulting from a dispersed TEI.
d. MFB and/or GPB – Evaluate the effect of degraded MSFN performance we are now experiencing on ground monitoring of the descent and ascent powered flight phases of the lunar landing mission for purposes of advising the crew of guidance system performance and need for switchover.
4. Perhaps you can think of some other thing effected by this situation and could suggest additional studies. Also, I may have indicated the wrong branch and assume you will correct that. As far as completion dates are concerned, I don't think this is real urgent. However, perhaps same preliminary results could be made available sufficient to know if we really have a problem or not. I'm not so sure we do but there seems to be panic growing in some quarters—–Frankly, MSFN performance is turning out to be substantially better than I ever expected a couple of years ago when I was bad mouthing its use.