Ascent advice

[indy91]

The braking phase is done in attitude hold mode, so you don't change your attitude anymore. And you correct your approach with the TTCA, so translation mode. With the Rate Err Mon switch in the RR position the FDAI shows the RR angles on the error needles and the cross pointer shows the trunnion and shaft rates at which the RR is currently tracking the CSM. Those displays are a really good aid in staying on course. The goal is to keep the needles centered, which means that the RR is pointing directly forward to keep tracking the CSM and that is how you want to approach the CSM. Just do some translational burst and see what it does to the needles on cross pointer and FDAI. Takes a bit of practice but it works really well. And of course once you get to the braking gates look at your range rate and reduce it to the amount required at that gate.

 

[sw34669]

fab thanks
ok, i have a strange compression issue. My A11 has been around 8 mins late so far
i finished CDI and CDH on time and started TPI 4 mins early, so 4 mins back good
TPI went well with nulled res, started and finished on time
At this point i started mid course 1
I waited and pressed PRO but the re-calc for for burn in 2 mins, same with MCC2 (res from MCC2 were 0 0 0)
I then seemed to be a lot closer than I should 85000 feet at 97FPS
I have also been losing lock as I got close I guess I need to pitch up (should the CSM be in the crosshairs of the LM reticule) for approach

When making the the 20FPS gate @ 3000 feet i just run out of energy eventually but i wasn't using the error needles as you've suggested

If you have a chance have a shuftie at this post MCC2 scenario just incase there's something horrific wrong with it. It's an action packed few hours

 

[sw34669]

 

[sw34669]

oh yes
feels i bet almost as good as collins LM appearing out of nowhere
massive grin
I had just missed the RR error needles

 

[MrFickles]

fab thanks
ok, i have a strange compression issue. My A11 has been around 8 mins late so far
i finished CDI and CDH on time and started TPI 4 mins early, so 4 mins back good
TPI went well with nulled res, started and finished on time
At this point i started mid course 1
I waited and pressed PRO but the re-calc for for burn in 2 mins, same with MCC2 (res from MCC2 were 0 0 0)
I then seemed to be a lot closer than I should 85000 feet at 97FPS
I have also been losing lock as I got close I guess I need to pitch up (should the CSM be in the crosshairs of the LM reticule) for approach

When making the the 20FPS gate @ 3000 feet i just run out of energy eventually but i wasn't using the error needles as you've suggested

If you have a chance have a shuftie at this post MCC2 scenario just incase there's something horrific wrong with it. It's an action packed few hours

I had no trouble getting to the CSM, I only had to thrust downwards (-Z) a little to get it back to the center of the COAS.
Energy-wise, I crossed 1NM at 35fps closure rate, then braked according to the gates on the flight plan.

If your speed is too slow, it may be because your TPI was 4 minutes early. The longer you stay in your CDH orbit, the more dV you need to intercept the CSM. The goal is to make the TPI burn when the CSM elevation angle is at 27.5 degrees. This just means that the CSM is at 27.5 degrees above the horizon.

 

[sw34669]

yes agreed my issue was not pitching flat to the CSM I forgot to flip the RR switch . Odd there's no mention of this in the gproc
alls well that ends well, easy job of getting back to earth now.

 

[n72.75]

You made it! Contrats!

 

[sw34669]

thank you sir and contrats to you too for such detailed work (and support) on all of this . I often wondered why they called it a hack to the moon. I get it now.

I re-did the braking phase last night a few times just for fun. One thing I can't get right is 100% nulling for station keeping. Even in pulse, the slightest tap of the translational key, is too far one way; reminds me of playing pong in the 1970s.

 

[MrFickles]

thank you sir and contrats to you too for such detailed work (and support) on all of this . I often wondered why they called it a hack to the moon. I get it now.

I re-did the braking phase last night a few times just for fun. One thing I can't get right is 100% nulling for station keeping. Even in pulse, the slightest tap of the translational key, is too far one way; reminds me of playing pong in the 1970s.

That's normal, I think its to do with the minimum impulse you can get on NASSP due to the timestep and whatnot. You do not need to strictly keep the CSM still in front of the LM for station keeping. As long as you are in a relatively slow drift, it's fine.

 

[sw34669]

cool. I also have a thruster out, in -Z that hasnt been helping me , all switch settings are nominal (AFAICS)

 

[sw34669]

oh my that explains the yaw and trouble slowing down in -Z. The thruster switch was fully on (grey). Cycling this off-hold-on-hold brought it back.

 

[indy91]

oh my that explains the yaw and trouble slowing down in -Z. The thruster switch was fully on (grey). Cycling this off-hold-on-hold brought it back.

Yeah, looking at input channel 32 in your post MCC2 scenario, one thruster fail signal is set, for thrusters 13 and 15 (A1U and A1F). That would be the forward, left quad, the upward and forward firing thrusters. If the LGC gets that signal it won't use those thrusters.

I don't believe this is a bug, it's just a bit strange behavior. The LGC gets signals from all eight thruster pair switches, to determine if it can use the thrusters or if they have failed. The Systems Handbook says about this:

Contacts 4, 5, and 6 [for the signal to the LGC] are mechanically linked (indirectly) to thruster pair switches. The position of the contacts is determined by the last actuation of the switch, i.e., the contacts form a memory device.

So this is different from the talkback and the actual valves. Even if the isolation valves circuit breaker is open the LGC can get this signal, without the valve actually being closed and with the talkback gray as if there was no problem.

I wonder how this happened though. I don't see the issue yet in your pre PDI scenario. So my theory is you switched the thruster pair switch for quad 1, system A to off some time on the lunar surface. Not sure if those switches are used anywhere in the surface checklist, I have to check.

 

[sw34669]

thanks. i think you're right it was during the testing phases that are checklisted to ensure they are all working.
it's a really easy thing to fix, i SHOULD have noticed, i've flown for 30 years, should have known better.My excuse is i was so engaged in the complexities of the ascent process and I dont have buzz to help. I have you guys so not on my own

 

[Thespacer]

Well done, anyway, it’s a great feeling. Plus, this thread should hopefully now serve as a point of reference for others going through lunar rendezvous for the first (or second) time.

As I mentioned in a separate thread, consider now having another go but this time also doing the CSM “mirror” tasks. One really is able to appreciate the engineering that went into both spacecraft, as it seems this was really the most complicated part of the mission for a variety of reasons, and all the navigation systems get a great workout.