Apollo 13 Launch Scenario: What should I expect?

Wedge313

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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.
 

rcflyinghokie

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We think it was an Option 9 midcourse but the upper pericynthion limit was changed to 135, this should give you an Indian ocean splash. Time of burn was 61:30 and leave inclination empty to get option 9A.

Might need some other tinkering though, its been a while since I have played with that burn. Give that a shot and see what your entry looks like.
 

Wedge313

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Backing up a bit, when we uplink the REFSMMAT, should we use ACTUAL or DESIRED?
 

Wedge313

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A question about maneuvering: I'm sure there's something obvious I'm doing wrong but I can't figure it out. I'm not sure I'm set up correctly. If I want to pitch or roll the stack I should be using the TTCA (translation), correct? But what I'm seeing when I attempt to maneuver using translation is the RCS system fighting itself. To get translation to work I need to have the mode control PGNS in either AUTO or ATT HOLD. And so when I attempt to maneuver, the ship tries to hold its current orientation by firing opposing quads. When I stop the translation the RCS fires until the ship is back at its starting orientation. It seems like I should be able to disable this attitude hold somehow but I'm stumped.
 

Wedge313

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Call verb 76
PGNS - ATT HOLD

That should do what you want.
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.
 

rcflyinghokie

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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.
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.
Did you make sure the RTCC and your LM are both using PTC REFSMMAT and its aligned properly? What did your maneuver pad look like?
Also, you can ignore the boresight star for this maneuver as it wasn't read up to the crew or used.
 

Wedge313

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I was questioning my alignment, so I re-did my initial coarse alignment, just to check that I did it correctly. Then I took an off-scenario detour and did a P52 alignment (I have an unfair advantage in that I can see the stars) and that looked good. So accepting that my alignment is OK, I went back and did my RTCC calculated MCC free-return burn. I just "trusted" the uplinked P40 F50 18 values, and ignored the FDAI and PAD roll and pitch. I'm at the 73:46 point of the scenario, barreling in towards the moon. I just finished the P52 sun alignment check, and that looked good.

There's just some things about the LM that I don't understand, like the ICDU O/I/M angles and their relation to the FDAI presentation, and that's throwing me off. When I did the P52 sun check, the P52 F50 18 showed RPY of 244, 316, 329. After maneuvering the FDAI showed RPY 244, 316, 329. So that looked good. But If I pull up V16N20 with that same orientation I get 125, 089, 309. And that makes no sense to me.

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?

Thanks.

EDIT: So from the transcripts on the Apollo Flight Journal there was a great discussion about this very issue that occurred right after the sun check at 75:52. Houston wants them to maneuver to an FDAI attitude of RPY 272, 083, 060. The crew asked for V49 numbers which were passed up as YPR 27100, 35500, 33000. And after some confusion and PROceeding on the V49 the F 50 18 shows up with the desired RPY 27172, 08301, 05999. I don't fully understand, but at least it gives me more confidence going forward.

Also, I think I figured out the RTCC procedure for calculating the PC+2 burn (it is covered in the RTCC Input Guide). I came up with a dV of 910 fps, giving me a splashdown at 142+27, which is in the ballpark. I'll keep playing with it.
 
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indy91

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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?

Now you are using the Return-to-Earth (RTE) targeting. There is a litte bit of an overlap with the TLMCC processor. The latter can be used until shortly before flying by the Moon. The RTE is used from entering the lunar sphere-of-influence until MCC-7. The RTCC MFD manual has a longer section about Return-to-Earth Targeting, so make sure to read that. You will need to use the Abort Scan Table first, with the "Specific Site" option at the input time of ignition (PC+2 hours). Your target is now the Mid Pacific Line (MPL). You need to give it a very rough estimate of your splashdown time, just so that it doesn't find a solution 24 hours earlier or later. So that should be about 143 hours GET. I hope that already helps.
 

Wedge313

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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.

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.

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.
 

rcflyinghokie

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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.
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?
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.
CO2 scrubber saturation is not modeled in NASSP, so you will always have a steady state CO2 level based on the crew on board.
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.
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.

I believe I had to alter my trajectory in order to be able to burn the manual burn :p
 

Wedge313

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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?
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.)

I believe I had to alter my trajectory in order to be able to burn the manual burn :p
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.
 

rcflyinghokie

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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.
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?
 

Wedge313

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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?
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.
 

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rcflyinghokie

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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.
I'll give it a look shortly and report back
Meanwhile, I just completed the manual MCC burn. It was much less exciting than in the movie!
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)
So I got to practice the midcourse burn twice, although not quite by the book, and I think I'm set to continue.
Very nice! Different to control pitch and roll with TTCA isnt it?
 

rcflyinghokie

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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.
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.

<PYRO> Descent-Engine-Start-Pyros 0 0.0000
1682526335256.png
 

Wedge313

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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.
 

rcflyinghokie

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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.
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.
 

Wedge313

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On we go to the LM-CSM Power Transfer procedure. After going through the steps I don't show any amps or volts on the BAT charger. Is this modeled in the simulation, or just another procedural error on my part?
 
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