Apollo 15 Post Orbital Insertion Procedures Question

[rcflyinghokie]

And for MCC-4, is it still using Option 4?

No, MCC3 and 4 are both Option 1 using the stored SFP unless you need to fix the post LOI ellipse.

 

[indy91]

Options 2 to 5 are all optimizing the total DV of both the midcourse correction and LOI. A byproduct of this calculation is the nodal target, that is the point where LOI would happen if LOI was an instantaneous maneuver. So the intersection (or node) between the incoming orbit and the desired lunar orbit. The nodal target is the time and position in space of that node. With that F30 button you are saving the nodal target (and some other stuff) in the second data table; the first one containing the pre-mission estimate. And that node is what mode 1 is targeting, no DV optimization or anything, just adjusts your trajectory so that it goes to that position at the desired time. In theory, if your deviation from the planned trajectory after MCC-1 and MCC-2 isn't too big, that gets you the same trajectory as running modes 2-5 again and reoptimizing the maneuvers again for MCC-3 and 4.

The mission techniques documents give another reason for using mode 1 for MCC-3 and 4 and not one of the DV optimization modes. Let me quote the Apollo 13 document:

There are three modes of targeting available for the H-2 mission; the first is the best adaptive path (BAP) , FR or NFR. The objective of this mode of targeting is to reduce the sum of the DV's
required for the translunar MCC's and the LOI maneuver to the smallest possible value which will result in the desired lunar orbit. Generally this mode will not be used beyond TLI + 30 hours for the following reason: As the MCC maneuver point gets close to LOI, the DV tradeoff between performing a given plane change at a MCC or at LOI becomes significant concerning translunar phase DV optimizations; that is, a given plane change DV at a MCC can reduce the plane change DV at LOI by an ever increasing amount as the lunar sphere of influence is approached. Therefore the BAP mode of targeting (which recognizes the small potential DV savings) would produce the corresponding plane change tradeoff. Thus the situation could occur where the BAP MCC DV would begin growing in magnitude even though the previous MCC had been executed perfectly. The situation would be comparable to preplanning a nominal mulit-impulse translunar MCC/LOI combination to save DV. Since DV is not that critical and because it is operationally desirable to freeze the nominal flight profile as early as possible, the BAP mode for the latter portion of the translunar coast is. generally undesirable.
Beyond the scheduled time of MCC-2, nodal (XYZ and T) MCC targeting is normally used. This type of MCC is targeted for the position vector and time of arrival at the nominal node between the lunar approach hyperbolic plane and the desired lunar orbit plane, thus providing a direct coupling with the desired lunar orbit. These nominal nodal targeting objectives are defined by the last previous BAP targeting computation; i. e., if the previous BAP MCC were executed perfectly (including navigation), the actual DV required for a subsequent nodal targeted MCC would be zero.

Case and point the actual Apollo 15 mission. For some SPS trouble shooting they let it burn the engine a bit longer on MCC-2 than needed. That resulted in a slightly larger MCC-4 than usual, 5.4 ft/s. And that larger maneuver caused some issues for the ground tracking. They couldn't define the orbital plane perfectly in the few hours of tracking between MCC-4 and LOI. The result was a not so great state vector (apparently only in the orbital plane) and to still fly over the landing site they had to add a 50 ft/s out-of-plane component to their DOI burn.

To be fair I haven't seen this effect of shifting DV from LOI to the MCC that much in NASSP, not really sure why. Maybe something in the targeting is still not as it should be. Or it doesn't apply as much to the later missions with the LOI/DOI instead of LOI-1/LOI-2.

 

[Wedge313]

Next, setting up for the LOI burn. A lot of the RTCC inputs seem to be already loaded? (LOI 1 apolune and perilune, Ha and Hp after DOI/LOI 2, landing site lat/long). What about the approach azimuth? Is that also already loaded? Where would I get that information if it needs to be adjusted? Couldn't find an example of how to go about setting the RTCC up for this computation, so there's a lot of unknowns here.

 

[rcflyinghokie]

Next, setting up for the LOI burn. A lot of the RTCC inputs seem to be already loaded? (LOI 1 apolune and perilune, Ha and Hp after DOI/LOI 2, landing site lat/long). What about the approach azimuth? Is that also already loaded? Where would I get that information if it needs to be adjusted? Couldn't find an example of how to go about setting the RTCC up for this computation, so there's a lot of unknowns here.

Those are preloaded with the mission parameters, so you won't need to touch them. Just remember you need the intersection solution that has the correct Hp and if both have it, then lowest dV.

 

[indy91]

You would find the approach azimuth in the spacecraft operational trajectory document (https://www.ibiblio.org/apollo/Documents/HSI-43615.pdf). For Apollo 15 it is -91° (equal to 269°, this isn't 100% consistent in the RTCC but it's the exact same angle). The RTCC MFD manual has a detailed section for the LOI calculation.

 

[Wedge313]

Back to the LOI preparation. I'm doing something wrong here, and I'm trying to work it out.

When I switch the REFSMMAT from PTC to the LOI orientation, which option in the RTCC should I select? I ask because after changing the REFSMMAT and running the LOI burn calcs I can get an orbit solution that looks good (60 x 170 ish) but the PAD gives me RPY for the burn of 289/056/077, and I believe (from looking at the Apollo 15 LFJ) that my RPYs should be 0/0/0?

Adding doubt, even though the PAD shows Ha and Hp of +170.0 and +60.1, when I run P30 my F 06 42 Ha and Hp show +04864 and -01484.

I'm obviously messing up somewhere, and I think I'm using an incorrect REFSMMAT.

 

[rcflyinghokie]

Back to the LOI preparation. I'm doing something wrong here, and I'm trying to work it out.

When I switch the REFSMMAT from PTC to the LOI orientation, which option in the RTCC should I select? I ask because after changing the REFSMMAT and running the LOI burn calcs I can get an orbit solution that looks good (60 x 170 ish) but the PAD gives me RPY for the burn of 289/056/077, and I believe (from looking at the Apollo 15 LFJ) that my RPYs should be 0/0/0?

Adding doubt, even though the PAD shows Ha and Hp of +170.0 and +60.1, when I run P30 my F 06 42 Ha and Hp show +04864 and -01484.

I'm obviously messing up somewhere, and I think I'm using an incorrect REFSMMAT.

You should be using a P30 REFSMMAT heads down for LOI using the LOI burn. In the maneuver pad page that should give 000 with a heads down attitude for the burn.

I still wouldn't worry about your N42 values on the CMC. If the maneuver pad has it correct and you have a good state vector then you should be fine. (Unless you are in LPO, then if you see negatives I would worry.)

EDIT: One document that might help with you understanding your REFSMMAT is the SCOT (Spacecraft Operational Trajectory) document. It has, among other great info, a REFSMMAT summary (pdf 169) for the mission.

 

[Wedge313]

LOI burn went smoothly, no issues. In a 161.3 x 63.8 orbit (close enough for now) (And no one was more pleasantly surprised than me.)

Question: Explain P20. The procedure in the AOH seems unrelated to the procedure in the G & C checklist. I can get the majority of the info the checklist asks for off the flight plan, except for the celestial body vector, didn't know what to enter here. And what is it's purpose? Are we trying to orient the spacecraft for all the photography we'll be doing?

 

[rcflyinghokie]

LOI burn went smoothly, no issues. In a 161.3 x 63.8 orbit (close enough for now) (And no one was more pleasantly surprised than me.)

Not awful but still a little off, I think you should be ok assuming your orbital plane is correct.

Question: Explain P20. The procedure in the AOH seems unrelated to the procedure in the G & C checklist. I can get the majority of the info the checklist asks for off the flight plan, except for the celestial body vector, didn't know what to enter here. And what is it's purpose? Are we trying to orient the spacecraft for all the photography we'll be doing?

P20 is an all inclusive program that allows rate and attitude control with respect to a reference point. Most of the P20 you will be using is designed to point the sim bay to the lunar surface while maintaining orbital rate.

The celestial body is basically the "star code" of what you are pointing to, in this case you want "star 50" which is the moon. The celestial body vector I believe will only be asked if using the VECPOINT option (option 1).

P20 has a lot of other uses as well, too much to explain here without being information overload, but if you have any specific use questions let me know.

 

[Wedge313]

Another roadblock: How do I use the RTCC to generate the LOI-2/DOI burn?

I've been playing around with this for a while, trying to learn how to use the RTCC. It seems to me the RTCC already knows where I want to be after the DOI burn, those values (HA 60 and HP 8.23) are already in the LOI Initialization page. So I would expect to use the LOI Processor for the calculation (right?). But at T 81h20m when I go to generate the DOI maneuver the LOI Processor is setting me up for what looks like a plane change burn (DVZ +164.7) at T 81h36m.

I went back to my initial LOI-1 burn (at 78h31m) and after the burn (with a 161.3 x 63.3 result) the LOI Processor looks like it wanted to have me do a plane change at 79h30m.

FWIW the Orbiter MAP MFD does show my orbit passing south of Hadley. But I have to zoom in quite a bit to see it.

So what is my best path forward. Am I looking in the wrong place to get the LOI-2/DOI calculation, or am I in a "you can't get there from here" situation? Was my initial LOI burn too far off, and I need to correct it?

For the initial LOI calculation I chose the Intersection solution (if I read the RTCC instructions correctly), and of the two solutions offered chose the one that gave me a HPC of 60 (the other showed HPC of 26). Do I need to rethink this? If I understand what's going on, the RTCC is making trade-offs to give me a solution that most closely fits what I'm asking for, and I went with the choice that resulted in a 60 mile perilune. Did I sacrifice too much in my required plane?

Thanks for taking the time to help me learn this stuff.

 

[rcflyinghokie]

So what is my best path forward. Am I looking in the wrong place to get the LOI-2/DOI calculation, or am I in a "you can't get there from here" situation? Was my initial LOI burn too far off, and I need to correct it?

I think you are in the incorrect place. You should be using the descent planning LM maneuver sequence to compute DOI.

Look under the DOI section of the RTCC Input Reference Guide.

 

[Wedge313]

Thanks for your guidance. After DOI I'm in a 64.2 x 8.6 orbit, not great but good enough?

My learning curve with the RTCC is basically class 5 vertical at this point. I appreciate the help.

And, has anyone come up with a way to get the lunar landmarks to display? They work in the regular Orbiter 2016, but not in Beta. (The visual is pretty cool at this lower altitude).

 

[rcflyinghokie]

Thanks for your guidance. After DOI I'm in a 64.2 x 8.6 orbit, not great but good enough?

I think you will be ok, and with respect to your path not being over Hadley, this is normal since you wont be landing for a few orbits, the ground track will move towards the landing site as you orbit. Also, what are you using to get your orbital parameters?

My learning curve with the RTCC is basically class 5 vertical at this point. I appreciate the help.

As was mine when I started using it! You are doing well so far!

And, has anyone come up with a way to get the lunar landmarks to display? They work in the regular Orbiter 2016, but not in Beta. (The visual is pretty cool at this lower altitude).

I think someone posted a way to do this in another thread, I have not tried it myself: https://www.orbiter-forum.com/threa...s-after-mcc-5-to-splashdown.40208/post-587927

 

[Wedge313]

Also, what are you using to get your orbital parameters?

I got them with V82 at the end of P40.

 

[indy91]

Well something definitely happened with LOI that made it not very accurate, ideally the orbit would be 60x170. But it looks good enough. And I don't think your orbital plane would be affected too much. After DOI you can calculate a PDI PAD (when you are in the LM, on the Maneuver PAD page and press the OPT button until you see it). If the crossrange is below 4 NM it is good enough.

 

[Wedge313]

So the errors in both my LOI and DOI have been bugging me, and I had one of those "aha!" moments, and think I figured it out. I went back to a save point before the LOI-1 burn and ran through the procedure again, this time ending up with an 170.1 x 59.2 orbit, which is more in the ballpark?

I'll continue from this point and see what the DOI burn results in.

 

[rcflyinghokie]

So the errors in both my LOI and DOI have been bugging me, and I had one of those "aha!" moments, and think I figured it out. I went back to a save point before the LOI-1 burn and ran through the procedure again, this time ending up with an 170.1 x 59.2 orbit, which is more in the ballpark?

I'll continue from this point and see what the DOI burn results in.

That looks like a great LOI! What was the "aha" moment?

 

[Wedge313]

Funny thing...turns out if you input inaccurate info you won't get the correct results. I'm embarrassed to say I had the wrong CSM/LM weights loaded in the DAP.

After the DOI burn I ended up in a 59.3 x 8.5 orbit. Pericynthion is lower than the flight planned 9.2 but it looks better than what I had.

 

[rcflyinghokie]

Funny thing...turns out if you input inaccurate info you won't get the correct results. I'm embarrassed to say I had the wrong CSM/LM weights loaded in the DAP.

After the DOI burn I ended up in a 59.3 x 8.5 orbit. Pericynthion is lower than the flight planned 9.2 but it looks better than what I had.

Haha yeah that certainly can have an impact!

And that is a bit lower than expected, but it shouldn't be an issue moving forward. @indy91 might be able to shed some light as to why the DOI processor put you in a lower Hp.

 

[Wedge313]

RE: low pericynthion (or is it perilune?)...I have to think it's something I'm inputting or not inputting correctly into the RTCC. I'm trying to generate the DOI Trim maneuver and the resulting orbit (according to the PAD) would be 59.2 by 8.6. All the previous PADs showed about that same Hp, so for some reason the RTCC thinks I want to be at 8.6.

Going from the RTCC main page I'm selecting TAR>LDP (Descent Planning). On the first page I'm leaving the HEI at 60.0. Selecting INI the HDP (altitude at PDI) is already set at 50000 ft. The other inputs I've made are the TH1 and TH2 times.

After that I been playing with the different modes and inputs trying to see what I can do to affect the resulting Hp (using the "push a lot of buttons until you get desired results" approach). The LM Maneuver Sequence/DOI will give me a 59.17 x 8.23 result. (Changing HEI to 9.6 has no effect). If I play with Single CSM Maneuver and CIR, DOI I can come up with solutions for a 59.18 OR a 9.61 circular orbit depending on whether I put 60.0 or 9.6 into the HEI field. Other MOD selections will either generate nothing (as in "you really don't want to do this maneuver") or give me a variation on the 59.1 circ orbit, the 9.6 circ orbit or the 59.1 x 8.23 orbit.

I thought this DOI Trim maneuver would be a chance to get me back to a 60 x 9.6 orbit, but I can't figure out how to do that. All I should need is a small RCS burp at apocynthion.

Thanks.