Apollo 15 Post Orbital Insertion Procedures Question

Wedge313

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Which meter display are you reading? Should be 4D as the test meter is modeled on earlier missions not J missions
7D gives me zero. 4D flickers, sitting basically at zero but with a discernable but very small fluctuation.

Was there some step I missed here? I didn't do anything about connecting the umbilicals, wasn't sure there was any way to do that. All I did was turn the switch on.
 

rcflyinghokie13

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The flicker is normal right now, its heaters cycling. When convection losses are added the heater current will be higher on the low end, but you will see it come up when additional heaters kick on.

7D is for J missions, but our CSM is not based on those, so 4D will show LM current.
 

Wedge313

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OK, I'm not understanding the REFSMATT/Alignment process. I just ran through the Uplink REFSMATT/ P52 option 1, then P52 option 3 sequence at the T+ 5h time window. But moving ahead to T+ 8h and performing the V49 maneuver expecting to line up on star #1 I'm again pointing in the direction of star #35. (So whatever I'm doing wrong, at least I'm consistent.)

The PTC REFSMATT Uplink seems to go ok. The P52 Option 3 goes well. When I begin the P52 Option 1, my FDAI #1 is at RPY 215, 084, 315 before proceeding and 119, 127, 355 after. So something is going on, right?

But after the V49 maneuver I should see star #1 in the SCT, and I'm looking at star #35. So I'm not getting something.

One question: I've been doing the Coarse Align, should I be doing Torque? Don't they both end up with the same result?

Here's the .scn file, I'd appreciate you looking at it and hopefully figuring out what I'm not doing correctly.

Thanks
 

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indy91

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To review what I'm doing with the RTCC MFD, starting with the main (first) page I select UTI, then REFSMATT. Using OPT I select PTC. I'm inputting a GET time of 005:10:00. Then I click CLC.

Sorry, I should have noticed this earlier. This is what you are doing wrong. The time that is preloaded there for the PTC REFSMMAT (200h something) is what you need to use to have the correct PTC REFSMMAT, not the current GET. The same PTC REFSMMAT is used for TLC and TEC so the time when it is valid was chosen to be the average time of TEI, taken into account the full launch window. We have already determined the time empirically that gives us the same REFSMMAT used on the actual mission. Sorry if that wasn't explained anywhere else.

EDIT: See the definition of the REFSMMAT types in the flight plan, page 1-5.
 
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Wedge313

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OK, thanks! So don't touch the time, uplink again, P52 Option 1 and I should be good to go again?
 

rcflyinghokie13

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OK, thanks! So don't touch the time, uplink again, P52 Option 1 and I should be good to go again?
@indy91 beat me to it! You are uploading an incorrect REFSMMAT indeed. You need to keep the preloaded time on the PTC REFSMMAT page (230:09:00).

When you are in the REFSMMAT page, you choose the REFSMMAT option (PTC in this case) and then hit CLC. From here you go to the uplinks page and uplink the desired REFSMMAT.

For PTC you don't touch that time at all. In fact, the only time you need to change the REFSMMAT time is if your TLAND changes and to get a liftoff REFSMMAT.
 

Wedge313

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The Apollo 15 Apollo Flight Journal has a nice discussion about this. As does the flight plan. Both I've read.... retroactively. So much to learn, so little time.

You need to have a NASSP Ground School website. Teach systems. Then a Procedures Training website to learn/practice procedures. Pass a test before you can download NASSP. Much better than allowing untrained people like me to use the simulation and constantly bother you with questions.:)

Thanks again.
 

rcflyinghokie13

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Oh man, there is so much to absorb I wouldn't know where to start with a ground school haha!

But hey, many of us who have been around for a while learned this all in stride as well, doing it, failing, asking questions, and repeating.
 

Wedge313

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On to the next challenge... using the RTCC to generate the MCC-1 PAD. I can navigate to the MCC page, entered the time I want to do the burn from the flight plan, selected option 4, but beyond that the RTCC Input Reference Guide has me stumped. "Tweak REVS1 until DOI DVZ = 0"? "Adjust LOI ignition time"? And a host of other entries that I have no idea where to start. I can't even find the field that displays DOI DVZ. (I did find a DV MCC field)

I can't find the "RTCC For Dummies" book on amazon, so I'm stuck and looking for help. Thanks.
 

indy91

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For once the actual manual for the RTCC MFD is useful here (Doc\Project Apollo - NASSP\Programmers Notes\ApolloRTCCMFD.pdf). There is a whole chapter called "Example: Midcourse Correction Planning". I would suggest reading the whole thing. The Apollo 15 targeting works exactly like the Apollo 13 one. I haven't added the Apollo 13 chapter yet, but the only big difference is that you use mode 4 and not mode 5. So basically read the whole chapter (including Apollo 11), then follow the Apollo 12 example, except that you use mode 4 and not mode 5.

The main difference between those modes is that mode 4 is setting up the lunar orbit correctly so that you can do the CSM DOI burn where previous missions did a LOI-2 burn. Orbit after LOI isn't circular, orbit after DOI isn't circular and the orbits need to intersect in the correct way to set up an orbit after DOI that will approach the landing site. In my experience only if you are far off the nominal trajectory, or if you launched later in the launch window, would you need to bother with additional tweaking of parameters for DOI, on the constraints page. So I think you can just skip that part.
 

Wedge313

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I didn't know about this document, I only had the reference guide ( figured "programmer notes" were for an elite few). Thanks!

This may be the elusive RTCC "rosetta stone" that I was looking for!
 
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Wedge313

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OK, just completed MCC-2. The RTCC document you pointed out has been very helpful. A few questions:

It looks like I can generate a state vector from either the Project Apollo MFD or the RTCC MFD. Is one better than the other?

Where can I find the criteria for deciding when to scrub a MCC?

How do I determine when ullage is necessary? How do I choose between two or four jets?

Finally, help me understand the SPS vs RCS Criteria chart in the G&C Checklist (Page 5-11 4-jet ullage as an example). If my CSM/LM weighs 98,000 lbs and I need to make a 4.0 fps burn, does the chart indicate a SPS burn with 4 sec ullage?

Thank You
 

indy91

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OK, just completed MCC-2. The RTCC document you pointed out has been very helpful. A few questions:

It looks like I can generate a state vector from either the Project Apollo MFD or the RTCC MFD. Is one better than the other?

For Apollo 15 I would use the RTCC MFD. The AGC uses a yearly changing coordinate system (only changes very slightly, one year worth of Earth precession). And the PAMFD being the much older MFD can only uplink state vectors for the coordinate system used by Apollo 7 to 10. The difference isn't larger, although Apollo 15 is already 3 years later, so the differences might already be somewhat noticable.

Where can I find the criteria for deciding when to scrub a MCC?

The mission rules document. The criteria I have been using for the MCC scenarios are basically this:

"LOI shall be targeted within these constraints:

A. The pericynthion of the approach hyperbola will be maintained within +/- 10 NM of HP target
B. The altitude of the node (between approach hyperbola and the desired LPO) will be maintained between -10 and +15 NM of HP target"

I find it easier to judge it by the DV of the calculated maneuvers. Unless it is 10 ft/s or even larger I would skip MCC-3. Doing MCC-4 is good for entering the desired lunar orbit precisely, so unless it is less than 1 ft/s or so I would always do it.

How do I determine when ullage is necessary? How do I choose between two or four jets?

The CSM burn schedule has ullage requirements: https://history.nasa.gov/afj/ap15fj/fplan/2-012.gif I'm actually not sure about 2 vs. 4 jets. Maybe if the CSM is very light you would rather use 2 jets to have a longer time for the propellants to settle but not such a large DV from it?

Finally, help me understand the SPS vs RCS Criteria chart in the G&C Checklist (Page 5-11 4-jet ullage as an example). If my CSM/LM weighs 98,000 lbs and I need to make a 4.0 fps burn, does the chart indicate a SPS burn with 4 sec ullage?

The ullage duration is just a function of total spacecraft weight, not the DV. If the propellant tanks are nearly full you aren't doing an ullage burn at all, that's why that curve is at zero for 82,000 lbs and above. The SPS vs. RCS criteria is basically a 0.5 second SPS burn. You want to use the SPS if you can, but don't want a burn shorter than 0.5 seconds. So that's basically what that curve is that is labeled "V_g". For 98,000 lbs it has 3 ft/s. So if the burn is more than 3 ft/s you use the SPS, otherwise RCS.
 

Wedge313

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Thanks for the explanation.

Next question: Where the heck in the LM is the RR GYRO SEL switch? I see it listed in the AOH but one (the LM 10 and subsequent) doesn't show a panel location and the other (LM 11 and subsequent) says panel 12 but I can't find it.
 

rcflyinghokie13

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Thanks for the explanation.

Next question: Where the heck in the LM is the RR GYRO SEL switch? I see it listed in the AOH but one (the LM 10 and subsequent) doesn't show a panel location and the other (LM 11 and subsequent) says panel 12 but I can't find it.
This is a tricky one! Its on the AOT frame.
 

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Wedge313

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Another RTCC MFD/MCC question...

I'm at the Apollo 15 T+ 55 hour point, and was generating the MCC-3 target load. Following the RTCC MFD Input Reference Guide I used Option 4. The MCC DV it calculated was 0.5 fps, so I was going to skip this maneuver. But the resulting Hp it shows is -493.3. Pretty sure I want an Hp around 60, right? So I tried running it with option 1 just to see what happened, the maneuver dV went up a hair but the Hp stayed at -493.

Just to run over where I've been, I've done two MCC burns so far. MCC-1 at T+ 11h56m required a dV of 19.6 and after the burn showed an Hp of +35.5. MCC-2 at T+ 30h55m had a dV of 4.3 and resulted in a Hp of -12.6.

With this MCC calculation showing an Hp of -493.3, that's not the trend I hoped to see and I'm not getting a good feeling about my trajectory. Is there something I should be tweaking to get Hp back around 60? Does MCC-4 fix this? Or will forces unknown to me magically nudge me into the correct orbit?

Thanks
 

indy91

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Where do you see that negative HP? On the Maneuver PAD? The Maneuver PAD shows the current HA and HP at the end of the maneuver, in whatever reference (Earth or Moon) that burn happens. That's not the trajectory numerically integrated to the actual periapsis, it's what V82 would show if you run it after the burn. MCC-3 is still in Earth reference, so it shows the HA and HP relative to Earth.

That is a bit of a compromise, because the HA/HP the Maneuver PADs during the actual missions isn't really consistent. All Return-to-Earth burns like TEI would show a HP for Earth reentry, even if it happens in lunar orbit. The MCC-2 and MCC-4 Maneuver PADs seem to have NA, not applicable, usually.

The display that has the actual perilune altitude is the Midcourse Tradeoff display, it shows it in "H PYCN". If that is what is -400 NM then you might have a problem. But if should be fairly close to 60 normally.

Or will forces unknown to me magically nudge me into the correct orbit?

That is a thing that happens, too. Earth and Sun are still pulling on the spacecraft as you approach the Moon. If you look at the Orbit MFD or the PAMFD you will see that periapsis is still changing, until just the last few hours before actually reaching the Moon.
 

rcflyinghokie13

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Also just to clarify, you did Option 4 for computing MCC2 and stored the SFP, and used the updated SFP when computing Option 1 for MCC3? If you use the preflight one, you might get some odd numbers in Option 1
 

Wedge313

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Yes, those values were from the PADs and V82s. So those still are in reference to earth? I guess I should know that, since I've done Apollo 8 and 11 and probably asked the same question before.

Looking at the H PYCN, it's showing 67.888. So maybe I'm not about to make a crater. Yet.

Thanks for the explanation. Pressing on.....

Also: Yes I stored the SFP (that's the F30,1; step?) after MCC-2.
 
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