See list attachedSeptember 27, 196868-PA-T-PA/Chief, Apollo Data Priority CoordinationC’ Mission Techniques
Attached are a list of ground rules and working agreements I compiled from my notes taken at the September 13 and 14 Mission Techniques meetings and the September 20 Lunar Abort meeting, all on the C' mission. This list is far from complete. Basically, these items are only the changes and additions to the material in the existing Mission Techniques documents already published, which are generally accurate. I put this together to document what I thought was agreed to. We will get together on October 2, 1968, at 1:00 p.m. to review this whole thing. Probably going through this list will be the easiest way. Based on that, TRW will prepare Xerox review copies of the following Mission Techniques documents for review and publication on the following dates:
Subject Review Publication
Earth Orbit and TLI October 10 October 21
Translunar MCC and LOI October 16 October 28
TEI, Transearth MCC, and Entry October 9 October 21
Also attached is a list of some of the action items coming out of these meetings.
September 27, 1968
C' LUNAR MISSION GROUND RULES AND WORKING AGREEMENTS
1. It has been established that all earth orbit operations prior to TLI will utilize the pre-liftoff REIPSNMAT. Furthermore, it has been established that all translunar MCC with the exception of the final MCC (at LOI -8 hours) will also utilize this same REFSMMAT. Of course, it is recognized that the direction of any MCC is completely random and it is possible that IMU gimbal lock could result if this were strictly adhered to. Accordingly, if it is determined that the middle gimbal angle during a MCC will be less than 45°, a new REFSMMAT will be relayed to the crew for that specific maneuver. In that event, a REFSMMAT yielding 0, 0, 0 on the FDAI when the spacecraft is in maneuver attitude will be utilized.
2. It is felt to be advantageous to utilize a single REFSMMAT for all lunar operations including the LOI maneuvers and TEI. Since the G&N is being activated for the lunar operations prior to the final MCC, it was decided to extend this procedure to include that maneuver. That is, the final MCC (at LOI -8) will also utilize the lunar orbit REFSMMAT. The lunar orbit REFSMMAT is defined as that platform orientation which will yield 0, 0, 0 on the FDAI 8-ball when the spacecraft is at a heads up, + X-axis forward, horizontal attitude at the time of LOI₂. This means that during the LOI₂ maneuver, which is performed retrograde and heads down, the FDAI display will be 0, 180, 0.
3. Pending agreement of MSFC, we have established a ground rule that if the COAS horizon check of TLI burn attitude has failed, the TLI burn will be inhibited (Berry, Paules, Huss).
4. It is possible for either the MCC-H or the crew to activate the CMC uplink program (P27) providing the crew has not inhibited it. The crew has a strong preference that they not be included in that activity. Therefore MCC-H shall do it whenever they send an update.
1. It has been determined that it is nominally not necessary to perform an IMU alignment while in earth parking orbit prior to TLI. The mission techniques which have been developed for a general lunar mission such as F and G have omitted the platform alignment as a part of the G&N systems evaluation, since it has been determined that other tests are adequate for that purpose without it. If these other tests reveal some problem or possible problems, a platform alignment is often required for resolution. Except for a late Pacific launch, this would ordinarily require utilization of the second TLI opportunity. On the C' mission there is time to perform a platform alignment and it is being included in the crew flight plan but it should be emphasized that it is optional and failure to perform it for some reason does not constitute sufficient reason for declaring the first TLI opportunity “no go”. Furthermore, no special procedures are being developed to include information obtained from the platform alignment in the TLI go/no go logic.
2. The spacecraft state vector will always be updated by the MCC-H during earth parking orbit prior to TLI. Since it is anticipated that the state vector determined by MSFN tracking will be superior to that obtained via telemetry from the SIVB IU that one will be used unless there is some obvious fault with it; in that event, of course, the IU state vector will be used. A significant point to be made is that no procedures are being developed for determining which of these two data sources is superior in real time. That is, there is no com- parison of state vectors to determine which is better. The MSFN is assumed to be better and will be used unless there is some reason to question its quality.
3. At present we are assuming that the EMS is not mandatory to fly the C' lunar
[note: pages 4 & 5 are missing in the source]
and the duration of the burn (a clock). It has been determined that burn duration for a booster operating within specifications can vary ± 14 seconds, which makes it essentially worthless as a data source for backing up cutoff. After lengthy discussions it was rather arbitrarily decided to establish a technique which puts maximum reliance on backing up the cutoff with the G&N and to use the EMS ΔV counter only as a last ditch device to use after it is obvious both the SIVB IU and the spacecraft G&N have failed. The technique selected requires the crew to monitor the G&N0 DSKY and to send manual engine shut down when the DSKY reaches an inertial velocity relayed by voice to the crew from the MCC-H while in earth perking orbit. This value of inertial velocity will be the anticipated nominal value biased to account for C&N systems dispersions, crew reaction time (including the DSKY display delay), and the SIVB delay in responding to the crew action. The EMS ΔV counter will be set prior to TLI with a MCC-H relayed velocity such that when it reaches zero, the crew should send the cutoff signal. This parameter shall also be biased. While of the same nature as the G&N this bias will be made substantially larger to assure that a premature shutdown, based on this cue, will not occur under any circumstance. A specific point to be made is that the manual backup signal will be sent if either the G&N or EMS reaches its limit. We are not waiting for both. The primary reason for this unusual procedure is that the G&N by itself, should provide the best possible backup as regards both accuracy and simplicity.
2. In addition to the parameters discussed in TLI paragraph lb, the only other parameters to be included in the pre-TLI pad message area a:
a. The mission elapsed time of TB6
b. The nominal burn duration
c. The nominal inertial velocity the crew should observe on the DSKY at the end of the burn including tail off.
3. In the event of a catastrophic spacecraft failure during TLI requiring premature shut down of the SIVB, the crew will utilize the abort handle, which reinitializes the clock and will perform an abort maneuver 10 minutes later to return to earth. The maneuver will be performed using the horizon as an attitude reference and an onboard chart solution for burn magnitude based on the crew display of G&N inertial velocity (VI) and/or EMS ΔV, noted at SIVB shut down.
1. All translunar MCC will be performed utilizing the G&N. Based on that, the MCC's are scheduled to occur at the following times:
a. TLI + 10 hours (if an emergency situation occurs requiring immediate return to earth, this maneuver may be scheduled as early as, but no earlier than TLI + 3 hours)
b. TLI + 20 to 30 hours
c. LOI – 20 to 30 hours
d. LOI – 8 hours
With regard to the final MCC, it has been determined that the minimum time required after the MCC to obtain adequate MSFN tracking and carry out targeting for the LOI is 4½ hours. In order to assure that ade- quate time will be available to compensate for unexpected occurrences and to avoid straining the MSFN targeting to its limit, it was decided to schedule the final MCC 8 hours before LOI. An additional benefit gained by this is that it provides the crew a final rest period prior to the especially taxing lunar orbital operations.
2. The MCC maneuvers have been scheduled to coincide with other crew activities such as the work/rest cycle. That is, they were not scheduled to optimize any trajectory considerations or anything like that.
3. MCC's prior to TLI + 30 hours will use the free return, best adaptive path (BAP) RTCC targeting mode. MCC's later than 30 hours after TLI require use of the Return-to-Nominal (X, Y, Z, T) mode, since the free return targeting mode does not work in this region. A test will be made to assure that any MCC using the X, Y, Z, T mode does not depart too far from free return. Specifically the trajectory following the targeted MCC maneuver will be projected ahead to approximately the time the space- craft exits the lunar sphere of influence and the magnitude required to hit the entry corridor will be determined. If this maneuver requirement if less than 45 fps, the MCC is considered to be within acceptable bounds. If greater than 45 fps, something serious must be wrong and the X, Y, Z, T mode must be abandoned in favor of a lunar flyby mode, which does pro- vide a free return. This is an unlikely, badly perturbed situation and precludes going into the lunar orbit.
4. A lower threshold has been established below which an MCC will not be carried out. It is based on the anticipated accuracy of the MSFN and is currently set to be 1 fps. That is, if the MCC is computed to be less than 1 fps, it will not be executed; if greater, it will be executed. The only exception is the last MCC (at LOI – 8 hours) which will be performed regardless of magnitude.
5. Any MCC computes to be greater than 3 fps will utilize the SPS. RCS is used for maneuvers smaller than 3 fps.
6. Residuals – All ΔV residuals will be trimmed to within 1 fps (MSFN 3σ accuracy). The only exception is the final MCC which will be trimmed to zero – all components.
7. All transearth MCC, including the first, will be performed for corridor control only, unless it is determined in real time that the predicted landing point is unacceptable for some reason (e.g., unacceptable weather or land masses within the footprint or in the FLA 2, or excessive return to base staging time). If a maneuver is required to relocate the landing point for reasons such as noted, above, the maneuver will be made large enough to provide acceptable landing conditions in the entire PLA I foot- print and at PLA 2. Wherever possible, of course, the recovery ships will be removed to a new location consistant with a 1350 nautical mile entry range.
1. In the event of a G&N failure during the LOI₁ burn, the crew will manually take over utilizing the SCS and will continue the burn to nominal completion. That is, the automatic EMS ΔV cutoff will be activated and used.
2. The attitude excursion limits for the LOI₁ burn are as follows:
a. Not to exceed 15° during the first 100 seconds.
b. Not to exceed 10° for the remainder of the maneuver.
These limits apply to both pitch and yaw. Violation of these limits will be determined by observing both sets of BMAGS, one of which will be driving the attitude error needles; the other set will be driving the FDAI 8-ball. A violation must be apparent on both these indications prior to crew takeover.
3. Since both sets of BMAGS are required to monitor the LOI maneuver, they must be considered mandatory for initiating the LOI burn.
4. The crew should monitor and manually backup the automatic G&N engine cutoff signal through use of the EMS ΔV counter and the event timer. Limits have been established whereby it is considered safe for the crew to await violation of both of these systems before taking over from the G&N. (Reference MPAD memo, 68-FM-73-400, dated September 17, 1968, subject: Onboard monitoring of the LOI maneuver.)
5. LOI₂ will utilize the same attitude excursion limits as LOI₁. However, the engine cutoff backup will be performed based on the event timer only. That is, the EMS ΔV counter will not be utilized for this purpose. In the event it is necessary for the crew to take over from a malfunctioning G&N, they will complete the burn on the SCS utilizing the automatic EMS ΔV counter engine off command.
6. ΔV residuals of the LOI burns will not be trimmed except for the X-axis of LOI₂, which will be trimmed to zero.
1. TEI will be targeted to land at 165° W longitude on a specified day of landing using minimum ΔV. The latitude of landing will not be directly controlled. This is the so-called CLA mode in the RTCC.
2. Targeting for the TEI maneuver and all transearth MCC will be aimed at achieving the steep, contingency entry target line, which provides a -6.48° flight path angle nominally.
3. The TEI maneuver will be targeted to limit the return inclination to be less than 40°.
4. ΔV residuals of the TEI maneuver will not be trimmed except for x-axis which will only be trimmed to within 2 fps.
5. Monitoring of the TEI burn will utilize the same techniques and limits as the LOI₁ burn. That is, the attitude excursion limits will be:
a. Not to exceed 15° during the first 100 seconds.
b. Not to exceed 10° for the remainder of maneuver.
These limits apply to both pitch and yaw. Violation of these limits will be determined by observing both sets of BMAGS, one of which will be driving the attitude error needle, the other set will be driving the FDAI 8-ball. A violation must be apparent on both these indicators prior to crew take over.
6. TEI will be performed in a heads down attitude.
7. In the event of a G&N failure during the TEI burn, the crew will manually take over utilizing the SCS and will continue the burn to nominal completion. That is, the automatic EMS ΔV cutoff will be activated and used.
1. The EMS will be set up to start automatically when it senses .05 g's and will be backed up manually three seconds after the ground computed .05 g time.
2. An entry attitude check is made by comparing the position of the horizon with spacecraft window markings approximately 5 minutes before entry. It is mandatory that this check be passed successfully or the G&N will be declared unacceptable for entry guidance.
3. The entry will be flown utilizing the G&N in the automatic mode. That is, the DAP will be enabled in all three axes prior to .05 g's.
4. REFSMMAT for entry shall be that which provides an FDAI display of 0, 0, 0 when the spacecraft is oriented heads down, blunt end forward, x-axis horizontal at the entry interface.
5. On the C' mission a non-skip reentry will nominally be utilized. That is, the entry range shall be limited to from 1200 to 1800 nautical miles. (Based on these limits the GNCS should never enter reentry P66.)
6. The useful operational footprint nominally is 1200 to 1450 nautical miles. (Simulations currently underway are expected to permit extending this to 1550 or 1600 nautical miles.) The normal reentry range for targeting and ship location purposes (i.e., PLA I) shall be 1350 nautical miles (which, if flown would preclude use of P65).
7. PLA 2 is defined as a contingency area end will be located at a range of 1800 nautical miles. PLA 2 will never be used unless PLA 1 is unacceptable for some reason and the G&N is working. If during attempt to reach PLA 2 the G&N fails, the crew will fly a constant G reentry until aerodynamic capture is assured and then will fly maximum range to get as close to PLA 2 as possible.
8. The SM/CM separation is to be combined with the pre-entry spacecraft attitude, horizon check. The separation pitch attitude has been defined as being the same as the horizon attitude check and yaw is 45° out-of-plane. Separation studies should be carried out, if they have not already been completed, to verify acceptability of this decision – not to optimize it.
C' ACTION ITEMS
1. Establish the TLI velocity cutoff bias values for the GNCS (V'±) and EMS (VC'). (MPAD)
2. Establish switchover point defining conditions under which the MCC-H will compute return-to-earth maneuvers to hit the “shallow” rather than the steep entry target line. (MPAD)
3. Determine what cues, if any, exist to give warning of impending GNCS failure. These are particularly needed to set the limit of the GNCS degradation we would accept and still initiate the TEI burn or the GNCS rather than SCS. (MIT)
4. Establish the spacecraft attitudes for the pre-entry horizon check. (FCD)
5. Establish tolerance on the horizon attitude check for GNCS go/ no go. (MPAD)
6. Confirm no SM/CM recontact problem (MPAD)
7. Establish GNCS entry monitoring procedures for the new short range entries. (MPAD)
8. Provide overall EMS check and burn procedure for RCS and SPS. (See page 50 of Entry) (NR)
9. Provide a P37 insertion limit. (MIT)
10. Establish which is more important, in targeting LOI₁
a. Proper altitude (60 x 60) or
b. Pass over the pseudo landing site (MPAD)