See list attachedJanuary 21, 196969-PA-T-10APA/Chief, Apollo Data Priority CoordinationF and G mission cis-lunar and abort plan
On January 8 a gang of us FOD types got together to develop a proposal on how we should use the LM for cis-lunar and lunar orbit aborts. In other words, how should the C' techniques be modified due to having the LM DPS available to backup or use in place of the SPS. A great deal of work has been done and documented by Carl Huss, the Flight Analysis Branch of MPAD, and the Apollo Abort Working Group and the results belatedly reported here are heavily dependent on that work.
First of all I'd just like to state a few facts and assumptions upon which the Abort Plan given in the attachment are based.
a. Except in the case of aborts from lunar orbit, the SPS will always be the primary abort propulsion system. That is, the maneuver will be made with the SPS, bringing along the LM, when possible, so that the DPS can be used as a backup if the SPS fails.
b. Since the SPS does not have enough propellant for TEI with the LM attached, we must reverse the order for leaving the moon if we want a TEI propulsion system backup. And, I guess we do.
c. There is a period during translunar coast – from TLI until about LOI – 20 hours that the fastest return to earth can be made directly using a maximum SPS burn after jettisoning the LM. After that period there is no advantage to direct returns and we don't ever suggest making one.
d. There appears to be no period wherein it is faster to make a direct return using the DPS than it is to perform a post-pericynthion maneuver following a 60 mile flyby.
e. It is always preferable to perform a lunar flyby than a direct return using the SPS unless we truly have a time critical situation, in which case we would only consider use of the maximum available ΔV solution which, of course, includes jettisoning the LM.
f. The fastest return trajectory including a lunar flyby is with a pericynthion altitude of 60 n.m. If we maneuver to provide a higher altitude, the trip time is most likely going to increase. This accounts for the use of 60 n.m. in the time critical flyby modes. Of course, the procedure must include making the standard regularly scheduled translunar midcourse corrections to achieve 60 n.m.
g. Although the real time situation (particularly spacecraft con- figuration has an overwhelming bearing on what should be done), it seems like a good idea to place the spacecraft on a trajectory targeted to the prime CLA as soon as practical, even though that causes an increase in trip time, and perhaps a second maneuver after pericynthion to speed it up.
h. Although we always list the SPS maneuvers as the prime mode and only utilize the DPS as a backup to the SPS, it is recognized that the crew and ground must be trained and prepared to carry out a docked DPS burn. Accordingly, numerous additional options are available to be agreed to either pre-flight or in real time wherein the DPS is used instead of or in addition to the SPS. For example, the desire to make a DPS system test may justify its use in a non-critical time situation or the use of both the DPS and SPS may provide a significant advantage given certain spacecraft system failures to provide greatest crew safety.
Finally – we briefly discussed how to handle partial LOI₁ Burns. First of all we are recommending the same procedures as C' in the event of guidance or control problems during LOI₁ – namely SCS MTVC rate command takeover and burn completion. This is proposed for all the same reasons as for C' – basically it results in a better situation. For SPS failures prohibiting completion of LOI₁, Flight Analysis Branch recommends ground targeted aborts using the DPS as preferable to the C' type “15 minute abort” SPS burn using on-board chart targeting. This is probably the best thing to do and I'm sure we'll talk about it a lot more before it finally is resolved. One thing to be emphasized though is that, since we have the DPS backup we don't have to be in such a hurry to take action after SPS troubles show up as we were on C'.
All of this will be thoroughly reviewed at a slam-bang Mission Techniques meeting scheduled for January 29.
CIS-LUNAR ABORT PLAN
Categories depend on when the need for the abort is recognized as follows:
CATEGORY I
From TLI until abort LOI – 20 hours (The actual time will be approximately at the equi-return time – direct return using the SPS vs flyby. This tradeoff will be biased as described in Note I.)
A. Time Critical
1. SPS direct return without the LM, to any CLA (ΔV less than about 8,000 fps). (See Note II)
2. DPS maneuver at pericynthion + 2 hours to any CLA following a 60 mile flyby. (1500 fps ΔV max.)
B. Non-time Critical
1. SPS (or RCS) burn at convenient time before LOI – 5 hours, to flyby pericynthion between 60 and 1500 n.m., to the prime CLA.
2. DPS (or RCS) burn at convenient time before LOI – 5 hours, to flyby pericynthion between 60 and 1500 n.m., to the prime CLA.
CATEGORY II
LOI – 20 hours until the last translunar coast midcourse correction at LOI – 5 hours.
A. Time Critical
1. SPS burn at pericynthion + 2 hours to any CLA following a 60 n.m. flyby.
2. DPS burn at pericynthion + 2 hours to any CLA following a 60 n.m. flyby.
B. Non-Time Critical
1. SPS or RCS burn at convenient time before LOI – 5 hours, to flyby pericynthion between 60 and 1500 n.m. to the prime CLA.
2. DPS or RCS burn at convenient time before LOI – 5 hours, to flyby pericynthion between 60 and 1500 n.m. to the prime CLA.
CATEGORY III
After LOI – 5 hours – or when propulsion system failures are recognized too late to do Category II.
A. Time Critical
1. SPS burn at pericynthion + 2 hours to any CLA following a 60 n.m. flyby.
2. DPS burn at pericynthion + 2 hours to any CIA following a 60 n.m. flyby.
B. Non-Time Critical
1. SPS or RCS at earliest practical time before MCC 5 (about TEI + 15 hours avoiding sphere of influence) to the prime CLA as fast as practical. (See Notes I and III)
2. DPS or RCS at earliest practical time before MCC 5 (about TEI + 15 hours avoiding sphere of influence) to the prime CLA as fast as practical. (See Notes I and III)
NOTE I : There is an important real time judgment factor influencing the non-critical abort techniques trading off reduced return time vs. large maneuvers which may modify the priorities.
NOTE II : The LM is jettisoned only in the case of Category I, time critical, SPS direct return aborts.
NOTE III : Normal return velocities shall be limited to less than 36,323 fps. Time critical aborts must provide entry velocities of less than 37,500 fps.
- Nov 14, 1968 – C’ Mission Techniques clean up – Translunar and Transearth (6.2σ)
- Jan 20, 1970 – The Apollo rendezvous can be shortened by 2 hours (3.6σ)
- Oct 25, 1968 – C’ Contingency Review (3.2σ)