See list attachedNovember 14, 196868-PA-T-249APA/Chief, Apollo Data Priority CoordinationC’ Mission Techniques clean up – Translunar and Transearth
On November 8 we went over the Translunar and Transearth phases of the C' Mission Techniques – pretty well cleaning all this up, I think. The following paragraphs describe the more significant decisions and agree- ments reached. They deal with block data, onboard navigation, and return- to-earth with no communications.
1. Block Data.
There had been considerable concern over the translunar block data targeting. As you recall, the maneuvers were designed to bring the spacecraft directly back to earth, often requiring a very large SPS maneuver. Block data for this type of maneuver will still be transmitted to the crew. However, it will ordinarily be used as the secondary mode, to be executed only if a minimum time return is essential due to space- craft systems problems. The primary mode during the period from MCC₁ plus three hours until LOI minus eight hours will be a lunar flyby. The flyby maneuver would always be executed at LOI minus eight hours (instead of the last translunar midcourse correction). It will be targeted to raise pericynthion to between 200 to 1500 n.m. and to result in a CLA landing. In summery, for each block data maneuver time, there will be two maneuvers transmitted to the crew- the old direct return and the new flyby mode.
There has been some confusion regarding the post-pericynthion block data maneuver transmitted for use after the LOI minus eight hour midcourse correction if something precludes going into lunar orbit. At this meeting we specified that this maneuver will be targeted for the fastest possible return-to-earth provided an SPS burn in required. However, if the prevent free return trajectory already provides a water landing or an RCS maneuver is adequate to do so, we do not recommend making an SPS burn just to get to a CLA using a block data maneuver.
2. Onboard Navigation
It appears there is no disadvantage to moving the first set of star/earth horizon observations earlier and to do so will significantly improve their quality. Accordingly, the flight plan guys of FCSD were requested to change the flight plan to include this activity immediately after the CSM/S-IVB separation burn – about two hours earlier than before.
As you recall, the first batch of sightings are used to determine the test value of horizon altitude as actually observed by the crew to be used in the CMC . This will be updated via the uplink program (P27), provided the update value differs from the pre-launch value by more than 4500 meters.
It is intended to update the onboard state vector utilizing the sextant observations. The CMP has been instructed to accept the update provided the ΔR does not exceed 50 n.m. and the ΔV does not exceed 50 fps during the first time a particular observation is processed. Exceeding, either of these limits indicates that something say be wrong with the observation and serves as a warning that it should be carefully redone. The second time the same observation is obtained, it should be accepted regardless of the ΔR and ΔV based on the assumption that the CMP has certainly done right this time and the state vector is truly that much in error.
The spacecraft calibration limit has been changed from .006 to .003.
A momentous decision was finally ranched, namely that the MSFN state vector shall be used for all maneuvers. Since it is uplinked into the LM slots in the CMC memory, it will be necessary for the crew to transfer it (UNZAP) into the CSM slots and after the maneuver to restore the updated CSM state vector into the LM slots (ZAP).
There shell be a new “go/no go” decision point regarding use of MSFN versus onboard navigation. It is currently estimated that at entry interface minus 15 hours, use of the MSFN state vector is preferable to onboard navigation for the final midcourse correction and entry initializa- tion. Accordingly, at that time the MCC-H will update the CMC state vector and will provide an EI minus two hour midcourse maneuver targeting load. In addition, they will inform the crew that this data load is good enough to complete the mission without further onboard navigation and the crew should discontinue sextant observations. If this cannot be done by that time, the crew should obtain the following sets of data to maintain the onboard capability until the ground determined values are considered acceptable.
EI minus eight hours – six star/earth horizon observations
EI minus four hours – six star/earth horizon observations
EI minus two hours – four star/earth horizon observations (obtained immediately after the final midcourse correction).
3. Return-to-Earth – No Communication
It has been established, of course, that the crew will use the return-to-earth program (P37) to compute minimum ΔV midcourse correction maneuvers for corridor control only. Based on the output of this program, we are able to do two additional things. One is to determine the time the spacecraft will reach 400,000 feet which is required as an input to the IMU alignment program to get a “nominal” IMU orientation for entry. The other information from P37 is a precision prediction of the landing point. However, in order to target for a short range entry, it is necessary to bias the P37 values of predicted latitude and longitude prior to inputting them into the entry program (P61). These biases, which are a function of predicted inertial velocity at the entry interface, will be obtained by the crew from a chart. They will be chosen to provide an entry range of 1350 n.m.
In order to insure capture during the initial part of entry the spacecraft will be oriented lift vector down until 1.5 g has boon achieved. (Note: This is exactly opposite to the normal technique with communication.) At that time, if the G&N has checked out, the crew will switch to auto CMC mode and continue a guided entry using their standard monitoring procedures.
In order to permit the crew to use the planets in place, of stars during alignment of the IMU, it will be necessary to know their unit vectors. Accordingly, it is our intention to include this information as pert of the crew data package specifically for each launch opportunity.