Wedge313
Well-known member
It's time to get back onto a free return trajectory. How do I set up the RTCC to calculate that? There are a few MCC choices that offer a free return but I'm not sure which to use, what constraints to set up etc.
This first one in the LM should be actual since you aren't performing a P52 option 1Backing up a bit, when we uplink the REFSMMAT, should we use ACTUAL or DESIRED?
It did! Thank you.Call verb 76
PGNS - ATT HOLD
That should do what you want.
LM PADs were a bit weird like this, yaw was not included on them because as you know it doesn't change burn direction. 13 of course had all sorts of confusion with using the LM for attitude control as well as the burns.It did! Thank you.
Now I need help understanding my midcourse calculation. Using Option 9 I'm able to generate a PAD for the docked DPS burn. The PAD gives me two values for orientation, roll 097 and pitch 079. The yaw is supposedly left up to MCC or the crew, and I understand how/why rotation around the yaw axis doesn't affect the direction of the burn. But at a roll of 097 on the FDAI, I have to yaw the ship to get to a FDAI pitch of 079, and the FDAI yaw value can only be changed by pitching. So I don't see how I can orient for the burn without all three values being fixed. The PAD also includes a boresight star, and if I maneuver to roll 097 and pitch 079 on the FDAI there is only one yaw value that will put that star in the COAS. So obviously I'm confused with what's going on here.
So I'm going to press on, it looks like I'm going to miss the moon and whip around, and then I'll work on the PC+2 burn. Another RTCC learning opportunity! I haven't looked at it yet, what am I doing for this burn as far as setting up the RTCC?
Is the other regulator open? What is your descent configuration at this point? And how did you initially pressurize the DPS and do the first burn?PC+2 burn seems to have gone OK, with one procedural issue. The procedure read up to the crew for the DPS burn had them close the DES He REG 1 with 10 seconds remaining in the burn. When I did that I got an immediate shutdown. I had to go back and re-do the burn, left the DES He REG 1 open and let it auto shutdown. Not sure what I did wrong configuring for the burn for this to happen.
CO2 scrubber saturation is not modeled in NASSP, so you will always have a steady state CO2 level based on the crew on board.After the burn they start thinking about the CO2 issue. I'm at 84:25 and still don't have any indication of CO2 rising. The voice transcript shows that Fred is looking at the PPCO2 reading in the LM, but my PPCO2 guage is unpowered at this point, even if I close the ECS DISP c/b. Not sure what to expect through this part of the scenario.
I had this issue as well, because there is not the same venting simulated in NASSP from the steam ducts of the LM (caused by the evaporator running) you wont shallow up to the degree the actual mission did.Finally, looking ahead to the midcourse correction planned for around 104+00, I used the RTCC to see where I was (I used Unspecified Area, FCUA) and it's only showing a required dV of 0.16 fps. That would put me in the Pacific Ocean about 700 nm SE of Samoa at 142:27. I don't know if that required dV will change over the next 20 hours, I'm hoping it does because if the Apollo 13 movie is any indication this midcourse burn was an adventure, I'd hate to miss out on doing it.
DES He REG 2 is barber poled. I configured by following along with the Apollo Flight Journal voice transcripts and the LM Contingency Checklist 2 Hour Activation and Docked DPS Burn checklists. The first burn to get back onto the free return went well, except I ended up with a 171 mile pericynthion and so needed a little more dV on the PC+2 burn. I could have missed something configuring but I went over it and nothing jumps out a me. (So I'm missing it, but at least I'm consistently missing it.)Is the other regulator open? What is your descent configuration at this point? And how did you initially pressurize the DPS and do the first burn?
Yes! I thought about intentionally altering the trajectory to create the need for the 7.8 fps dV maneuver. That should be fun on its own.I believe I had to alter my trajectory in order to be able to burn the manual burn
It shouldn't kill the engine right away, either that's something incorrect in the sim or a step was missed. You don't by change have a save before your PC+2 I can check?DES He REG 2 is barber poled. I configured by following along with the Apollo Flight Journal voice transcripts and the LM Contingency Checklist 2 Hour Activation and Docked DPS Burn checklists. The first burn to get back onto the free return went well, except I ended up with a 171 mile pericynthion and so needed a little more dV on the PC+2 burn. I could have missed something configuring but I went over it and nothing jumps out a me. (So I'm missing it, but at least I'm consistently missing it.)
Yes! I thought about intentionally altering the trajectory to create the need for the 7.8 fps dV maneuver. That should be fun on its own.
Here's a save just before the PC+2 burn so you can see how I was configured. Thanks for looking, I'm curious what steps I missed.It shouldn't kill the engine right away, either that's something incorrect in the sim or a step was missed. You don't by change have a save before your PC+2 I can check?
I'll give it a look shortly and report backHere's a save just before the PC+2 burn so you can see how I was configured. Thanks for looking, I'm curious what steps I missed.
As it was in real life as well! It was very anticlimactic in reality and since it was a corridor control, it really wasnt time critical or super dV critical (though they did shut down early to prevent overburn, which would necessitate flipping around 180 in pitch to correct since they couldnt use -X jets)Meanwhile, I just completed the manual MCC burn. It was much less exciting than in the movie!
Very nice! Different to control pitch and roll with TTCA isnt it?So I got to practice the midcourse burn twice, although not quite by the book, and I think I'm set to continue.
Following up, it looks like you didnt fire your descent start pyros when you initially powered up the DPS. That is why turning off the reg immediately is killing your DPS.Here's a save just before the PC+2 burn so you can see how I was configured. Thanks for looking, I'm curious what steps I missed.
Meanwhile, I just completed the manual MCC burn. It was much less exciting than in the movie! As I mentioned before, my RTCC calculated dV required to get into the corridor was only 0.17 fps, so I needed to find a way to work around that and get myself off course. What I decided to do was leave my current trajectory after the PC+2 burn untouched, and then conducted the MCC burn following their procedures and burn time, with the earth in the COAS and oriented retrograde. After shutdown I re-did the RTCC calculation again, and it showed a required dV of 6.8 fps to get back into the corridor. I then I rolled the stack 180 degrees and re-did the procedure, except now the earth was in the COAS oriented posigrade. I used the same burn time. After shutdown I ran the RTCC calculation again and it showed I needed 0.61 fps to get back into the corridor. A little RCS trim and I was back where I wanted to be. So I got to practice the midcourse burn twice, although not quite by the book, and I think I'm set to continue.
Maybe? It would have been the helium pressure digital display. However our pressures are kind of cheaty at the moment, you still would have seen a change.OK. I knew something was wrong. I wasn't comfortable with the DPS pressurization, figured I messed it up. Is this something I might have caught if the pressure gauges were powered? Thanks for looking.