Apollo 11 LOI Issue

Paraso

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Hello!
I'm extremely new to NASSP ( which I am loving :) ), and I've finally managed to reach LOI-1 in 11, however at this point I've been experiencing.

I reach the P30 External DV checklist for LOI-1, I input all of the required values, and everything goes well. I continue through the checklists until I reach "Maneuver to LOI Burn Attitude". Here I insert the attitude values, once again everything goes well. I go through the SXT star check, and afterwards the SPS Prethrust. Going through the SPS Prethrust I am maneuvered to an attitude completely different from my burn attitude, which I thought was odd. Eventually I reach TIG - 30 and come across the step to reload N33 and N81 values which I do, and later on I get checklist items to maneuver back to the correct burn attitude. Afterwards I have another SXT star check, and eventually a step around TIG - 10 (F 06 18 Auto MNVR to FDAI RPY Angles) Which again maneuvers me to an attitude completely different from my burn attitude, and it stays this way up until the end of the burn.

I've attempted to change the FDAI RPY angles for said step, however when the burn begins I am automatically maneuvered to the same incorrect attitude. What am I doing wrong here? Am I missing something?
 

indy91

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Have the sextant star checks gone well? So can you see the star in the sextant? And if you went through with the burn in the attitude that the computer wants, did it lead to a good orbit? Also, can you post the two attitudes, the one on the Maneuver PAD and the one from the computer. We tend to be very close to the flight plan and actual mission with the attitudes, so we can probably determine that way which attitude would be the "good one".
 
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Paraso

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Thanks for your response! It's nice to talk you you again
I'd say the sextant checks have gone well, when I put the angles into the DSKY the sextant points fairly accurately at the star listed on the pad.

The attitude from the Maneuver PAD is
R 17900
P 24500
Y 00300
And looks like this around the start of burn:
The attitude from the computer is
R 17499
P 29774
Y 00591
And looks like this around the start of burn: Just did a burn with the computer attitude, I ended up in -100k by 9M orbit
 

jalexb88

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Just to confirm, when you did the step to "reload N33 and N81 values" you are indeed reloading the PAD values right? Don't just re-enter the ones you see on the DSKY because they could have changed a bit from the PAD ones I think.
 

indy91

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Neither of these attitudes makes much sense to me. Are you sure that attitude is from the LOI-1 Maneuver PAD? There are also Maneuver PADs for contingeny TEIs in the same timeframe. Could be from that. Especially the roll angle, it's 180° wrong from what LOI-1 normally is.
 

Paraso

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Neither of these attitudes makes much sense to me. Are you sure that attitude is from the LOI-1 Maneuver PAD? There are also Maneuver PADs for contingeny TEIs in the same timeframe. Could be from that. Especially the roll angle, it's 180° wrong from what LOI-1 normally is.
Thats odd... yeah heres the pad I'm getting all of my stuff from:
 

Paraso

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Just to confirm, when you did the step to "reload N33 and N81 values" you are indeed reloading the PAD values right? Don't just re-enter the ones you see on the DSKY because they could have changed a bit from the PAD ones I think.
Yeah I'm reloading the ones from the pad, can confirm that the ones I see on the DSKY are different from the pad ones when I reach those steps
 

indy91

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So, I get nearly the same attitude as on your Maneuver PAD if I use the launch REFSMMAT for the PAD calculation. So you probably still have the same alignment of the IMU as on the launch pad. Which is quite weird, because during translunar coast there are two P52 option 1 which should have changed the alignment. Early in the mission it gets changed to a PTC REFSMMAT and then on LOI day (before MCC-4, if it happened or not) it gets changed to a landing site REFSMMAT. Did anything unusual happen during those P52s?

That in itself wouldn't screw up the LOI-1 burn, so there must be something else going on, also likely alignment related.
 

Paraso

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So, I get nearly the same attitude as on your Maneuver PAD if I use the launch REFSMMAT for the PAD calculation. So you probably still have the same alignment of the IMU as on the launch pad. Which is quite weird, because during translunar coast there are two P52 option 1 which should have changed the alignment. Early in the mission it gets changed to a PTC REFSMMAT and then on LOI day (before MCC-4, if it happened or not) it gets changed to a landing site REFSMMAT. Did anything unusual happen during those P52s?

That in itself wouldn't screw up the LOI-1 burn, so there must be something else going on, also likely alignment related.
Alright, that might explain it. I skipped both p52 option 1's I had no clue how to do them properly and my angles would always be very far off. Are you able to give a quick explanation for how to do them? I have no clue what the coarse vs torque is for, the sct always ended up pointing into the middle of nowhere for me, and I have no clue what to do with the shaft and trunniun steps in the checklist.

Other than that, all of the other p52s went well
 

indy91

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Do you get any program alarms during P52 option 1? We recently had a bunch of alarms during Apollo 9, but that seems to be specific to the Apollo 9 software and procedures.

There is a very detailed description of P52 in this document: https://www.ibiblio.org/apollo/Documents/j2-80-E-2448-REV1_text.pdf PDF page 621.

But I'll give you the short version. When you do a P52 option 3 you are just doing a realignment, so fixing any drift or errors during previous P52s. The attitude reference stays the same, so usually an alignment that has some meaning (90° pitched up on the launchpad for example). At the end of the option 3 you get three angles, usually small adjustments to the IMU attitude, which get send to the IMU in small pulses, which is called pulse torquing, so that the IMU is perfectly aligned again. With small angles this happens very quicky.

During a P52 option 1 (and 2 and 4) you are changing the reference for the alignment. So the direction where the IMU would have all zero angles. For that the IMU has to be rotated by some large amount usually. There are two options for this. Coarse aligning, which is very fast, or pulse torquing, which takes quite a while. During the coarse alignment option you get a NO ATT light and the IMU will not drift by the same amount the spacecraft drifts. So if your attitude rates aren't perfectly nulled during this procedure then you will get some larger errors during the sextant marks and some larger adjustment angles at the end of P52. With the pulse torquing option the IMU keeps on doing its job, so even if you wouldn't do any sextant marks the alignment stays as good (or as bad) as before the P52 option 1.

EDIT: Oh, and while you can technically skip the P52 option 1, I would strongly advice against it. And once the LM gets powered up the LM gets its initial alignment from the CSM. The descent programs in the LGC will not work with the wrong kind of alignment.
 
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Paraso

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Do you get any program alarms during P52 option 1? We recently had a bunch of alarms during Apollo 9, but that seems to be specific to the Apollo 9 software and procedures.

There is a very detailed description of P52 in this document: https://www.ibiblio.org/apollo/Documents/j2-80-E-2448-REV1_text.pdf PDF page 621.

But I'll give you the short version. When you do a P52 option 3 you are just doing a realignment, so fixing any drift or errors during previous P52s. The attitude reference stays the same, so usually an alignment that has some meaning (90° pitched up on the launchpad for example). At the end of the option 3 you get three angles, usually small adjustments to the IMU attitude, which get send to the IMU in small pulses, which is called pulse torquing, so that the IMU is perfectly aligned again. With small angles this happens very quicky.

During a P52 option 1 (and 2 and 4) you are changing the reference for the alignment. So the direction where the IMU would have all zero angles. For that the IMU has to be rotated by some large amount usually. There are two options for this. Coarse aligning, which is very fast, or pulse torquing, which takes quite a while. During the coarse alignment option you get a NO ATT light and the IMU will not drift by the same amount the spacecraft drifts. So if your attitude rates aren't perfectly nulled during this procedure then you will get some larger errors during the sextant marks and some larger adjustment angles at the end of P52. With the pulse torquing option the IMU keeps on doing its job, so even if you wouldn't do any sextant marks the alignment stays as good (or as bad) as before the P52 option 1.

EDIT: Oh, and while you can technically skip the P52 option 1, I would strongly advice against it. And once the LM gets powered up the LM gets its initial alignment from the CSM. The descent programs in the LGC will not work with the wrong kind of alignment.
It looks like I am indeed getting a program alarm during P52 Option 1, looks like it's 112. I'll see if I can run through the TLC again and actually do the P52 Option 1's this time. I appreciate your help, indy.

Edit: Reloaded a save just before the p52 option 1, looks like im not getting the program alarm this time
 
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indy91

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112 is "Mark reject with no marks being accepted". You mark with the Q button on the keyboard and reject a mark that was just done with the E key, if it was a bad mark. So if you are pressing E at some random time (by accident or so) and there haven't been any marks then you get the 112 alarm. So should be a fairly harmless alarm.
 

Paraso

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112 is "Mark reject with no marks being accepted". You mark with the Q button on the keyboard and reject a mark that was just done with the E key, if it was a bad mark. So if you are pressing E at some random time (by accident or so) and there haven't been any marks then you get the 112 alarm. So should be a fairly harmless alarm.
Got it, silly me :LOL:
I successfully went through the first P52 Option 1 and among other things my pitch appears to have flipped 180 degrees, which I think is good news. I just remembered, I had another run where I did both P52 Option 1's (Albeit very inaccurately) and the attitude values I got were vastly different from what I have now, let me know if these make any more sense.

R 358
P 179
Y 327

Still working my way through the translunar coast, I'll keep you posted.
 

Paraso

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So I made my way all the way to LOI, and this time it was arguably worse than last time? First of all, in all of the P52's following the first option 1 P52, the SCT in its automatic mode would point nowhere near the star designated for that marking (This also applies to the burn SXT star checks). Second, the MCC burn had a similar case to the LOI scenario, where in one of the steps it would rotate to an attitude different from the pad attitude. Third, the pad given values for LOI put me in an attitude not too different from the one the computer gave me (relative to the moon) in the original post, and again this time the computer stepped in and made that problem even worse. Finally, not even seconds after the burn began, the spacecraft desperately tried to keep up with (what I believe were) rapidly changing atittude values, and at some point I think it pointed near pro-grade.
I am the worst at this

Edit: I think it's likely I messed up the preferred P52's
 
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Thespacer

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Finally, not even seconds after the burn began the spacecraft desperatley tried to keep up with (what I believe were) rapidly changed atittude values, at some point I think it pointed near pro-grade
That’s annoying, but a known problem with docked vehicles if you are using the non-beta version of Orbiter. Are you using the beta version?

Don’t lose heart, we’ll help get you into Orbit. The price of entry is high in terms of understanding the sim, but it’s well worth it.
 

Paraso

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That’s annoying, but a known problem with docked vehicles if you are using the non-beta version of Orbiter. Are you using the beta version?
I am indeed using the beta version, I've followed all of the steps detailed in the v8 installation guide on here
 

indy91

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I guess if you aren't in the burn attitude the computer wants at ignition then it will also try to do large maneuvers and possibly spin out of control.

Can you maybe post a scenario just before a P52 option 1 (either for PTC or landing site REFSMMAT, doesn't matter)? Just so that we can see if everything is set up correctly for it in the computer.
 

Paraso

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I guess if you aren't in the burn attitude the computer wants at ignition then it will also try to do large maneuvers and possibly spin out of control.

Can you maybe post a scenario just before a P52 option 1 (either for PTC or landing site REFSMMAT, doesn't matter)? Just so that we can see if everything is set up correctly for it in the computer.
Unsure if you meant before the beginning of the p52 checklist or before the markings themselves, I did the latter, let me know if you need the former.
 

indy91

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Hmm, I can see that the sextant isn't quite tracking the target star. But that's about all I can tell from this. So yeah, a scenario before you start P52 would be more helpful.
 

Paraso

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