What if Pete Conrad had NOT entered P66

[Dandy]

Apollo 12 has always been one of my favorite missions to research. I wanted to know how a precision landing was accomplished and seeing how close they landed to Surveyor was so intriguing to me.
My question is a two parter:
1. If the commander never enters P66 to take control, what is the computer programmed to do precisely? Can someone describe it to me?

2. If Conrad had not entered P66, where EXACTLY would the LM land? I believe we have enough information to simulate where it would have landed. If we know what the computer WAS going to do just before he took control, we could calculate approximately where the LM would have landed. My reason for wondering, I am very curious just how close to Surveyor it would have landed.

I have always wondered why they took manual control if the computer was programmed to land automatically. Doesn't it seem more dangerous (aside from the computer landing the LM in a crater or on a boulder)? I do realize they wanted to be in control of the lander because they are pilots and they didn't want their fate to be left up to a computer but is that the only reason? In the simulator, did they ALWAYS practice taking control in the final moments or did they ever let it land itself? Lots of questions I Apollogize.

[Obviousman]

The sequence goes automatically from P64 to P65, a fully 'fully automatic' landing mode. No crew ever did that, though; they all went from P64 to P66, the 'semi-automatic' landing mode.

Where would it land in P65? Wherever the LPD was indicating.

[Dandy]

The sequence goes automatically from P64 to P65, a fully 'fully automatic' landing mode. No crew ever did that, though; they all went from P64 to P66, the 'semi-automatic' landing mode.

Where would it land in P65? Wherever the LPD was indicating.

That's what I need to search, program 65. Thank you Obvious

[Obviousman]

This from the AFJ:

When the Braking Phase Guidance programme, P63, reaches the preselected values, the guidance programme switches automatically to programme P64 (Approach Phase Guidance). This is basically the same as P63 but with a new set of targets but, in addition, provided window-pointing logic for the Landing Point Designator (LPD) operation. The LPD was a scale etched onto the LM forward triangular window, on the Commanders side, which the Commander could sight along to view the landing area to which the Apollo LM was being guided. The computer calculated the look-angle (relative to the forward LM body axis, ZB) and displayed it on the DSKY to assist the Commander in his LPD operation. The guidance programme switched automatically from programme P64 to programme P65 (Velocity Nulling Guidance) when the TGO reached a preselected value (See Fig. 4).



The P65 programme was used for an automatic vertical descent to the surface of the Moon by nulling all components of velocity to preselected values, if this was required. There was no position control during this programme. At any time during the operation of automatic guidance modes (P63, P64 or P65) the crew could call-up optional programmes P66 (Rate of Descent) or P67 (Manual Guidance) through the DSKY. During the P66 operation, the crew could control spacecraft attitude with the computer commanding the DPS throttle to maintain the desired altitude rate. This would normally have occurred near the end of the P64 programme, near low gate, prior to switching to P65 programme for manual control of the final touchdown position. Programme P67 maintained navigation and display operations for complete manual control of the throttle and altitude. This was not a 'normal' mode unless the programme, P66, was inoperative.

[Obviousman]

From Phil Parker of Space UK:

I thought I'd look into this question of automatic LM landing a bit deeper -- in the pre-mission NASA MSC and contractor (MIT) manuals to see what they said.
Basically, they said that the landing phase was designed to be automatic but would provide for crew visual assessment of the landing site and, if required, to provide capability for pilot take-over from the automatic control -- which is what happened on the actual Apollo missions.

Under the automatic guidance, a vertical descent was initiated when the TGO (time to go to landing) was less than 12 seconds or at an altitude of 200 feet and would terminate on landing. A rate of 5 fps would be used throughout an automatically controlled vertical descent. The crew would need to disable the descent engine when the footpad probes touched the surface. (See notes 1 and 2 below).

The vertical descent guidance used a routine that nulled the lateral (horizontal) velocities while accepting the commanded vertical rate from the ROD (Rate Of Descent) switch. The vertical rate was also controllable by manual throttle control.

Note 1: An earlier NASA MSC document said that the LM vertical descent would have started at 100 feet altitude and rate of descent would have been 3 fps.

Note 2: I'm not sure what would have happened, under automatic guidance, if the TGO was 12 seconds or less and the LM found itself at a higher than 200 feet altitude? I assume the crew would have taken over using manual control before this happened? [This will be more a consideration for the new lunar module cargo delivery flights]

Phill Parker
spaceuk

http://www.collectspace.com//ubb/Forum29/HTML/000469.html

[VQ]

2. If Conrad had not entered P66, where EXACTLY would the LM land? I believe we have enough information to simulate where it would have landed. If we know what the computer WAS going to do just before he took control, we could calculate approximately where the LM would have landed. My reason for wondering, I am very curious just how close to Surveyor it would have landed.

I seem to remember, printed somewhere, a graphical representation of each of the landings and how their designated landing point moved as the CDR adjusted course in P66. Maybe in Digital Apollo by David Mindell, but I am not 100% on that. Worth a read either way, though, if you haven't read it already.

Lots of questions I Apollogize.

Oh. No.