Don’t turn off the landing radar

See list attachedOctober 29, 196969-PA-T-134APA/Chief, Apollo Data Priority CoordinationDon’t turn off the landing radar

A ripple just passed through our system, which I probably ought to document for the record. Pete Conrad called the other day suggesting that it might be a good nominal procedure to inhibit (V58E) landing radar data from the PGNCS at about the time it exits the Descent visi- bilty phase (P64). Ordinarily, this would be when they initiate manual control (P66) at about 500-ft. altitude. After polling interested MSC and MIT people on this, we have recommended against it and the crew has concluded even though it was agreed that the accuracy of the naviga- tion probably would not be significantly affected and there is a slight possibility of some spurious data getting in, particularly below 100-ft. altitude. (In fact, I think everyone agreed that if there were a way to inhibit the velocity data at that point, that would be a good thing to do.) The primary reasons for advising against this procedure were:

a. Landing radar altitude data is highly desirable during this part of the descent and V58 stops everything.

b. DSKY operations are undesirable if they can be avoided.

Consideration was given to changing the landing radar velocity weighting factor to zero in P65/66/67 but this is also not recommended (although it may be before the flight) because that technique stops the velocity data too early in the descent.

Although the decision is to leave the crew procedures as they are, this was probably a worthwhile review of this volatile subject and may yet result in a change in the weighting factor as Apollo 11 landing radar analysis is further defined.