Apollo 15: Lunar Ascent Preparation and RTCC Procedures?

[Wedge313]

Still not getting the tweak burn.

What sort of dVs should I expect for a tweak burn?

I've run through this five times. I'm obviously missing something. When I do the TAR>REN>TI>DIS>CLC>ENG>CLC after cutoff I'm getting tweak values in the order of -00082, -00029, -00321.

After cutoff my V82 orbit looks like 45.1 x 9.1. If I burn those tweak values I end up in a 40.0 x 3.9 orbit.

If I skip the tweak burn and press on through the rest of the procedure I've been able to rendezvous a few times. But I'd like to try to figure out what I'm doing wrong with the RTCC.

 

[rcflyinghokie]

At this point hard to say without seeing how it was preloaded before launch and how your ascent cutoff went. A pre liftoff scenario with your values in would be very helpful here.

Those values could be correct based on the ascent burn cutoff, where the CSM is, and such. But your orbit results concern me haha. So I really would like to fly what you have and see if I can replicate your results.

 

[jalexb88]

Still not getting the tweak burn.

What sort of dVs should I expect for a tweak burn?

I've run through this five times. I'm obviously missing something. When I do the TAR>REN>TI>DIS>CLC>ENG>CLC after cutoff I'm getting tweak values in the order of -00082, -00029, -00321.

After cutoff my V82 orbit looks like 45.1 x 9.1. If I burn those tweak values I end up in a 40.0 x 3.9 orbit.

If I skip the tweak burn and press on through the rest of the procedure I've been able to rendezvous a few times. But I'd like to try to figure out what I'm doing wrong with the RTCC.

In the Two Impulse page, do you have the parameters set correctly? With the OFF button you should type in: P51,15,1.7,26.6,130; This is what the page should look like:

(BTW, this is an Apollo 14 testing scenario so the T1 & T2 times are not correct here, T1 should be insertion + 3 minutes & T2 is your TPI time)

Also in the ENG page make sure THR is set to "LM RCS +X (4 quads)" L2

 

[Wedge313]

I grabbed this save from one of my attempts, from about 12 minutes before liftoff.

 

[indy91]

Did an ascent with that scenario. I was very smart and opened the PAMFD after insertion, which can sometimes lead to a CTD with the External MFD (which seems to be an Orbiter bug rather than NASSP as it can happen with other MFDs, too). But anyway, just before I did that I calculate a tweak solution and got 35 ft/s. The inputs you use seem correct, I probably used a slightly different T1 and T2, but it shouldn't matter too much.

So the issue could be anything from wrong liftoff time, initial landing site vector, IMU alignment etc. I'll have a look. The tweak burn calculation is probably accurate, but I'll take a look at that as well.

Edit: Ok, so one difference I am seeing is the liftoff time. If I calculate a fresh time in your scenario I get a liftoff time that is 15 seconds later (171:35:12 GET), which could easily cause the larger tweak burn. That will basically give you an offset position at TPI (you will be further behind the CSM than desired), but otherwise the trajectory is fine for a rendezvous, so it would work even without tweak. I don't know why the time is different, maybe you calculated the ascent maneuver with the MPT enabled and it had a different CSM trajectory or something. Difficult to say. I'll try launching with that updated time and see what kind of tweak it gives me there.

Btw, about the MPT. It is a total failure on my side that it required in any way to fly a mission right now, even Apollo 15. I'll work on removing any case where it is required, the learning curve for the RTCC MFD increase tenfold if you need to use the MPT, definitely not something for your first mission without MCC support.

Edit 2: Did an ascent with the updated liftoff time. Tweak burn DV vector is now: -1.7 -12.5 -2.0. So almost entirely out-of-plane. That likely is an IMU alignment error, Align Plane MFD shows a RInc of 0.14°. DVX and DVZ being close to 0 means it's a good insertion over all, including the right liftoff time. So definitely an acceptable insertion, just not the greatest P57s I guess.

 

[Wedge313]

Maybe I'm working from a bad save point on the P57s, I did have an issue with that earlier but after a lot of effort my last ten or so P57s all seem to go OK, my largest error was 00004.

Question: Like you did, I've been running through the RTCC ascent planning a second time around 30 min before lift-off, and I have seen that change in lift-off time (also small changes in the PAD). In my ignorance I've been ignoring the new time and sticking with my originally calculated time. I wasn't sure what might have caused the change in time and didn't want to mess with it.

I think what I'll try is a quick RTCC ascent planning about 30 min before lift-off, and use those new numbers for my P12 lift-off. I've been through the whole RTCC ascent planning process enough times, I can get through it pretty quickly. Then I'll see what kind of dVs I get for the tweak.

I guess my lift-off was close enough that the LGC could still P34/P35 its way to a good rendezvous. But I'm in no hurry, I'd like to learn to do this correctly. Probably go back to the end of EVA 3 and work forward.

Thanks for looking at this.

 

[rcflyinghokie]

Yeah going back to before lunar powerup and liftoff is probably a good idea, at the very least for practice. And certainly double check your liftoff times, I think an updated one was read up about an hour before LO? So that would be a good time to update everything to make sure your P12 matches as well as your P57 time.

 

[Wedge313]

I don't know why the time is different, maybe you calculated the ascent maneuver with the MPT enabled and it had a different CSM trajectory or something.

I'm still playing with this, getting more puzzled. I think it might be that I've been using a bad CSM SV?

I ran through this a few times starting at the end of EVA 3. I didn't notice any real difference in my steps, which only means that whatever I'm doing wrong I'm repeating.

Where I noticed a difference was at about 171:00. At 171:00 the flight plan has us uplink the CSM SV (if required) . If I don't uplink the SV my lift off time is 171:34:57. With the CSM SV updated and uplinked the lift off time changes to171:35:12.

If I use the updated CSM SV and 171:35:12 lift-off time my tweak burn dVs end up in the range of -0002.0, +0000.7, and -0004.7.

My problem may be a combination of RTCC ignorance and somehow grabbing a bad CSM SV at some point in the process? I don't know how the MPT active vs. inactive plays into this. But it may only be an issue with me starting the process with a bad CSM SV.

Anyway, I've done the tweak a few times now, and think I'll just move on. I don't fully understand what I might be doing wrong initially, but updating the CSM SV seems to have corrected it.

 

[rcflyinghokie]

I'm still playing with this, getting more puzzled. I think it might be that I've been using a bad CSM SV?

I ran through this a few times starting at the end of EVA 3. I didn't notice any real difference in my steps, which only means that whatever I'm doing wrong I'm repeating.

Where I noticed a difference was at about 171:00. At 171:00 the flight plan has us uplink the CSM SV (if required) . If I don't uplink the SV my lift off time is 171:34:57. With the CSM SV updated and uplinked the lift off time changes to171:35:12.

If I use the updated CSM SV and 171:35:12 lift-off time my tweak burn dVs end up in the range of -0002.0, +0000.7, and -0004.7.

My problem may be a combination of RTCC ignorance and somehow grabbing a bad CSM SV at some point in the process? I don't know how the MPT active vs. inactive plays into this. But it may only be an issue with me starting the process with a bad CSM SV.

Anyway, I've done the tweak a few times now, and think I'll just move on. I don't fully understand what I might be doing wrong initially, but updating the CSM SV seems to have corrected it.

I am wondering if you uplinked an incorrect CSM SV somehow prior with MPT. If your MPT was active its going to use the MPT maneuver/vector to determine state vector, if inactive it will use the current state of the vehicle at the time you select.

 

[Wedge313]

I just finished docking (again). I've run through the entire lift-off through rendezvous five times now, I think I've got the gist of it. At least the PNGS stuff, AGS is still a mystery but I'm going to leave that for now. Moving on....

I need to get a P30 burn for the LM after separation. I could grab the one they used off the Apollo Flight Journal, it would probably suffice. But do I want to generate one from the RTCC?

 

[rcflyinghokie]

I just finished docking (again). I've run through the entire lift-off through rendezvous five times now, I think I've got the gist of it. At least the PNGS stuff, AGS is still a mystery but I'm going to leave that for now. Moving on....

I need to get a P30 burn for the LM after separation. I could grab the one they used off the Apollo Flight Journal, it would probably suffice. But do I want to generate one from the RTCC?

So we don't have LM impact targeting yet I don't believe, still waiting on documents. You should be able to use the flight plan ir AFJ values without a problem. I'm on mobile right now but I will link you a document outlining how to use EMP99 to burn the LM "unmanned"

EDIT: You can use the RTCC to perform the P99 uplink and the P30 values.

You can go to the maneuver pad page and manually enter the TIG and dV values there and uplink them first.

Then you can use the UTI->EMP page to uplink the P99. You will see there are a few uplinks on there and it will cycle as you press NUM. After you uplink the P30, you will go to the EMP page and make sure Uplink number is 0, then uplink. After it is complete, you will press NUM to cycle the uplink to the next one and uplink it and so forth. You need to uplink 0, 1, 2, 3 in order.

The timeline book should have the proper configuration for the LM for jettison and using P99. I would exercise caution using time acceleration after jettison since the LM will be holding attitude until the burn time.

The burn itself was initiated via ground as well, but since we don't have a DSKY interface capability yet via RTCC, you will just hop into the LM and use the DSKY following the attached procedure. Be sure to run a V96 before starting.

 

[Wedge313]

Thanks. Seems like a lot of work to crash the LM into the moon!

 

[rcflyinghokie]

Thanks. Seems like a lot of work to crash the LM into the moon!

Haha well when there is nobody in the LM to drive, workarounds had to be in place

You essentially have to fly it unmanned, so these erasable memory programs were designed to do just that. Remember RCS burns were normally manually fired (under computer guidance) so they had to make it so not only the burn program worked unmanned, but it could fire RCS without an astronaut using the TTCA.

 

[Wedge313]

Well, finally found something I'm good at. Managed to crash the LM on my first try.

 

[rcflyinghokie]

Well, finally found something I'm good at. Managed to crash the LM on my first try.

Nice, did the EMP program and watched the computer burn the RCS?

 

[Wedge313]

Yes, followed your instructions and it worked out well. RCS burn ended up with a 65.8 x -32.6 orbit, not exactly per the flight plan but it achieved the desired result.

 

[rcflyinghokie]

Yes, followed your instructions and it worked out well. RCS burn ended up with a 65.8 x -32.6 orbit, not exactly per the flight plan but it achieved the desired result.

Yeah using the flight plan values and time of course will change the orbit depending on your current orbit, but until we get better impact targeting data it is close enough!

 

[Wedge313]

OK, now let's get ready for TEI.

At about 219:00 we're supposed to uplink the TEI REFSMMAT. I think to do that I need to figure out the TEI maneuver first, which will produce the TIG I need for a P30 REFSMMAT? Once again I'm lost on the RTCC, not clear on the process.

To generate a P30 REFSMMAT I need a time, and I can't manually enter that. It seems the only way to get that time is by calculating the burn first?

For the TEI burn TAR>ENT seems to get me to the page I need to work with but I don't know where to go from there.

On a bright note I think I was able to figure out how to generate the info for the Shape Burn. It looks like we'd be using the TEI REFSMMAT at that point. I didn't have that yet, so for practice I generated the PAD using a P30 REFSMMAT at the shape burn TIG.

But I think I need to figure out the P30 REFSMMAT based on the TEI burn TIG first, and the do the shape burn using that REFSMMAT. So I'm stuck at needing to figure out how to calculate the TEI burn.

Once again any guidance is appreciated.

P.S. Is there a subsat for us to launch, or will we just simulate that?

 

[rcflyinghokie]

To generate a P30 REFSMMAT I need a time, and I can't manually enter that. It seems the only way to get that time is by calculating the burn first?

This is correct, you need the maneuver itself in order to generate a P30 RESFMMAT.

For the TEI burn TAR>ENT seems to get me to the page I need to work with but I don't know where to go from there.

Yeah this is the correct page. This area needs a few revisions especially on the guide but here is how you do it and this is all with MPT Inactive:

TAR->ENT->AST-> Under TYP choose Lunar Search and SIT you will type "EOM" without the quotes. This tells it so do a lunar return search for the end of mission coordinates.

Then under TIM you enter your desired TEI TIG and under TZ you want your predicted landing time (you can get both of these from the flight plan) and leave everything else as is.

Click AST and then CLC and it should give you some entry and burn parameters. Check that these look correct and then proceed to click RTE.

On the RTE page, You are just setting up the burn parameters. You can leave COL and AST alone as its set up to compute the first burn prediction in the "primary" column. REF stays on CUR. Under MAN, you want to set up an SPS burn prediction so type CSUX (this is CSM, SPS, Undocked, External dV) and then under ULL you can use the flight plan ullage by clicking UL and typing 4 13 and this is a 4 jet 13 second ullage. Leave everything else alone and click DIS and then CLC. This should compute your first return to earth column and the splashdown information.

Click SPL and type P to save the splashdown target (this gets uplinked to the CMC with retrofire external dV uplinks) and then click TRA and type P to save the maneuver.

Now you can compute not only the maneuver pad but the P30 TEI REFSMMAT. Go back to the RTCC main menu and UTI->REF and choose P30 Heads Up and compute the REFSMMAT.

You can then use the uplinks page in the RTCC to uplink your burn (TEI and TEMCC burns you are using the "retrofire external dV") And of course you can uplink your desired REFSMMAT here as well (make sure its the last in the uplink chain so it's not overwritten)

On a bright note I think I was able to figure out how to generate the info for the Shape Burn. It looks like we'd be using the TEI REFSMMAT at that point. I didn't have that yet, so for practice I generated the PAD using a P30 REFSMMAT at the shape burn TIG.

Oh very nice! There are other methods we use for the shaping maneuver in RTCC like the general purpose maneuver calculator, but it's still good practice using other methods!

But I think I need to figure out the P30 REFSMMAT based on the TEI burn TIG first, and the do the shape burn using that REFSMMAT. So I'm stuck at needing to figure out how to calculate the TEI burn.

So this would be the case for using the MPT once again, to do it this way, you would need to compute the shaping burn, put it on the MPT, then compute a TEI using a vector time after the shaping burn and compute that P30 REFSMMAT.

If you already did a shaping burn I wouldn't worry about it now, but that is how you would get a REFSMMAT for a later burn. I can explain this more if need be as it does require MPT use.

P.S. Is there a subsat for us to launch, or will we just simulate that?

Sadly not yet

 

[Wedge313]

After the shape burn, when I go to P00 (V37E 00E) I have a steady COMP ACTY light. V96 will get rid of the light, but if I go back to P00 the COMP ACTY comes back on. I don't know what routine might be running, but how do I stop it? Thanks.