CSM HGA reacq mode

[Miriam]

Now after spending some time in lunar orbit doing essentially nothing except watching the systems (aka flying a nine hour rest period) I think I found a flaw in the reacquire mode of the CSM high gain antenna: looks like it doesn't switch back to wide beam once the signal is lost. When I switch to wide beam manually it does acquire earth, but not when the switch is in narrow or medium. Interestingly, auto mode works just fine: it freezes the antenna when the earth sets and reacquires by itself when it rises again, it even switches from wide to narrow or medium beam automatically (you can see that in the typical 'nudge' on the AGC meter when the autotracking has just barely acquired earth and the antenna switches from wide to medium/narrow beam by itself). However, it doesn't do that in in reacq mode, so I think that the problem lies there.
Oh: and is it possible to increase the resolution of the pitch and yaw knobs a little? Manually pointing the HGA a lunar distances is quite annoying right now, even in wide beam.

 

[n72.75]

I will take a look into this. CSM HGA auto-tracking and tracking modes was the first feature that I added to NASSP, there was a bug that @indy91 found with the whiparound flag a few months ago, and I fixed. It's possible that I broke reacq beam-switching at the same time... I will look into it.

 

[n72.75]

I identified the issue and pushed a fix. Will probably get merged tomorow.

There is a short delay timer that prevents switching modes every timestep, as this could cause oscillation between beam widths or notrack/auto/manual. In Reacq mode this timer was not incriminated in the correct place, which reacq mode to get "stuck" in whatever beamwidth it was in when it lost signal. Easy fix, hard problem to find, considering it took well over a year . Thank you for the detailed description and feedback.

 

[n72.75]

Update: fix has been merged.

 

[Miriam]

Jupp, that's a lot better. I'll dig for a translunar quicksave and try that in PTC when the HGA hits its scan limits. See if some gremlins hide there.

Easy fix, hard problem to find, considering it took well over a year.

Well, I'm flying the mission (Apollo 11) with the AFJ next to it. At about 85:00:00, they seemed to have a little problem with the reacq mode, which led me to the idea: hey, let's try that in NASSP, see what happens. I didn't spend much tought on the HGA before, even less on the reacq mode. But nine hours of doing nothing can be quite boring...?

 

[Miriam]

Well, no gremlins there. Tracks earth, hits its stops (even switches back to wide then), returns to the set angles once the signal is lost, reacquires, switches to medium/narrow beam once signal strength ist high enough.
The only thing I could criticise is that the gimbal limits are a little bit to generous. According to this, max. pitch angle at 270° yaw should be +70°, but it does go up to 75°. At 90° yaw, it should stop at -6° or so, but it tracks up to +6 or so.

 

[n72.75]

Glad to hear it's working now!

I plan on continuing to work on these, including better shadowing, interference, and side lobe behavior. I'll take a look into the gimbal limits while in at it.