Apollo 9: P52 Opt 1 (Preferred) at T+5:10:00 Question

Wedge313

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Hi again, I'm coming up on the Apollo 9 first SPS burn. Flight plan calls for a P52 Opt 1 alignment, followed by an alignment check. I'm not understanding something here....

I've copied the PAD, uplinked the target load and run P30. Then the PAMFD Checklist has us start P40 which displays F50 18 (which for me displayed my current RPY of 190,350,003. My PAD RPY is 000,356,001), then select P00.

Then the checklist leads me into P52 Opt 1. My new F 06 22 ICDU angles show the same as my current RPY. What REFSMMAT are we supposed to be aligning to ? I haven't uplinked a new REFSMMAT. The flight plan pg. 1-2 has a comment "The preferred IMU orientation for SPS No. 1 is calculated onboard, and the IMU is realigned to that orientation during the fourth night pass". When/how was I supposed to calculate that?

If I was doing my own RTCC, I think I would have uplinked a P30 REFSMMAT to do this burn. But I'm missing the preferred orientation. As a result when I V49 to the SPS-1 burn attitude my orientation is wrong, my SXTS check has me staring at the earth.

Please let me know what I'm doing wrong here. Thanks.
 

thermocalc

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hi Wedge313,
maybe i may help you this time :)
when you do P30 followed by P40, next you can do the P52 option 1, and so you should be able to realign the platform (depending on which attitude you are before, you may risk a gimbal lock upon torquing, if you get the alarm just yaw 30 deg one direction or the other and recycle via V32 until you see you can torque it, normally it works for me to avoid it). you should do it at around 5h10m (the p52 option 1)
After you may do the alignment check, and if i remember well you are supposed to move the whole CSM spacecraft to get the star centered in the optics.
after, when preparing for the sps-1 burn, setting the PAD RPY angles via V49 , at the TIG you should be close to 0-0-0.
hope it works for you.
 

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Wedge313

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(depending on which attitude you are before, you may risk a gimbal lock upon torquing
This is my issue, when I do the P52 opt 1 there is no torqueing, the RPYs before and after the "NO ATT" are the same. I'm not changing anything.
 

indy91

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P40 is calculating a preferred REFSMMAT the same way as the RTCC would do with the P30 (heads up) REFSMMAT option. Run P30, make sure V48 has the right trim angles because they used in the REFSMMAT calculation, and then enter P40 for just the first display. Then you should get 0,0,0 for the SPS-1 burn attitude.

It just so happens that the SPS-1 REFSMMAT is nearly identical to the launchpad REFSMMAT. From the transcript:

004:53:03 Roosa: Houston confirms the PAD. I would also now like to give you your gimbal angles used in the PAD REFSMMAT for SPS-1.

004:53:14 McDivitt: Go.

004:53:16 Roosa: Roger. It's roll 00, pitch 359, yaw 001.

When you enter P40 later again, does it not give you 0,0,0 as the burn attitude? The sextant star problem is because it's a heads-up alignment and it will usually need to be done a lot of time before TIG. Kind of difficult to get it right in the Checklist MFD. Sometimes the check needs to be done before the P40 checklist starts, sometimes it can be done at the "nominal" time between 10-15 minutes before TIG. In this case the flight plan has the sextant star check at about 5:30h GET.
 

Wedge313

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Run P30, make sure V48 has the right trim angles because they used in the REFSMMAT calculation, and then enter P40 for just the first display. Then you should get 0,0,0 for the SPS-1 burn attitude.
I did the DAP V48, took the gimbal angles (PTRIM, YTRIM) off the PAD. When I run P30 it looks like it loaded everything correctly from the uplink. After the last PRO the flashing V37 shows up, and I enter 40E to start P40. F 50 18 pops up with 190,350,003, which are my current RPYs showing on the FDAI. Should this be showing my PAD RPYs of 000,356,001?

I'm going to go back to some earlier save point and run through this again.
 

rcflyinghokie

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I did the DAP V48, took the gimbal angles (PTRIM, YTRIM) off the PAD. When I run P30 it looks like it loaded everything correctly from the uplink. After the last PRO the flashing V37 shows up, and I enter 40E to start P40. F 50 18 pops up with 190,350,003, which are my current RPYs showing on the FDAI. Should this be showing my PAD RPYs of 000,356,001?

I'm going to go back to some earlier save point and run through this again.
You just hit the 40E on the F37 of P30. Then you can exit P40 with V37E00E and enter P52 Option 1 which will have your P30 REFSMMAT in the "desired" slot ready to torque.
 

Wedge313

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You just hit the 40E on the F37 of P30. Then you can exit P40 with V37E00E and enter P52 Option 1 which will have your P30 REFSMMAT in the "desired" slot ready to torque.
That's what I do. But when I get to the P52 option 1 there's no real change in attitude, just a degree or so maybe, as if the new REFSMMAT is the same as the previous. I'll go back and re-do the simulation from some point well before I get the PAD and uplinks, maybe figure out where I went wrong.
 

rcflyinghokie

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That's what I do. But when I get to the P52 option 1 there's no real change in attitude, just a degree or so maybe, as if the new REFSMMAT is the same as the previous. I'll go back and re-do the simulation from some point well before I get the PAD and uplinks, maybe figure out where I went wrong.
As @indy91 said, this first P30 REFSMMAT is almost identical to the launch REFSMMAT so you wont see much change.
 

Wedge313

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As @indy91 said, this first P30 REFSMMAT is almost identical to the launch REFSMMAT so you wont see much change.
OK, cancel the emergency..... after re-doing the P52 opt 1 a few times, it looks like I'm following the procedure correctly. Everything works as advertised, except for the star check, the PAD wants me to check a star that's behind the planet. But the burn goes OK, I just needed to listen to you guys and accept the fact that the REFSMMAT really doesn't change much.

On the bright side, I'm redeeming myself by doing a really good job on the Daylight Star Check :).
 

rcflyinghokie

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OK, cancel the emergency..... after re-doing the P52 opt 1 a few times, it looks like I'm following the procedure correctly. Everything works as advertised, except for the star check, the PAD wants me to check a star that's behind the planet.
Which is behind the planet, the sextant star check for the SPS-1 or the daylight star check?
 

rcflyinghokie

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The sextant star check, for the P40 orientation. The one that shows up on the PAD for the SPS-1 burn.
Hmm it should be 30 minutes before the burn, maybe the pad is using the wrong star check time?

EDIT: No it's computed for 30 minutes before the burn also, and you should be optics up 30 minutes before the burn at burn attitude since its a heads up orientation.
 

Wedge313

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I think this was one of the early attempts, I deleted all the other quicksaves. But this should show you the PAD and what I was looking at at about 5:40 or about twenty minutes before the burn.
 

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rcflyinghokie

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This scn is about 8 minutes before the burn. The star check is TIG -30min.
 

Wedge313

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That's the only save I have before the burn, I started the V41N91 a while before the save and was trying to figure out my error. I abandoned that scenario because in real time, following the PAMFD checklist for the P52 and following Alignment Check, and eventually the V49 to the burn attitude, by the time I got to the SXTS check all I saw in the SCT was planet.

But you've got me thinking about something.... following the PAMFD checklist, the Alignment Check seems to eat up a lot of time. I'm probably doing it incorrectly. Could you describe the procedure to me, maybe I was eating up too much time doing too much maneuvering, and getting to the star check too late, after it passed beneath the horizon? I've been getting to the check around 5:40, about 20 minutes before the burn. So that's probably where I'm going wrong.
 

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Hello,

Maybe some of these quicksaves I did during my second practise run for 9 help? Note that they are generated running the release 1944 of NASSP 8 beta.

Best regards,
 

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Wedge313

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Thinking that doing the star check too late was my problem, I found a save point at 4+57, just before I did the target load uplink, and ran through the whole procedure again. To expedite the process I maneuvered to my expected burn attitude first, hoping to avoid a 405 alarm I've been getting when starting P52. Then I did the P30, started P40, V37N00, and into the P52 opt 1.

After doing the P52, I skipped the Alignment Check, because I don't really understand what I'm doing with this procedure and it's been eating up a lot of time. I went right to the V41N91 star check, beginning at about 5:19.

By getting to the star check earlier than I have been, my SXTS star (15) was in view. But while it was close to the SCT cross-hairs, it was not close enough. It was not in view in the SXT. This may be because I'm omitting the Alignment Check?

But my goal here was to see if the SXTS was in view if I did the star check earlier than I have been doing, and it was. However, at 5:29:30 the star was right on the horizon, and by 5:30 it was obscured. This is probably because my orbit (109.4 x 100.2) is a little lower than the flight plan (112 x 109), so I'm moving faster.

But I think if I can learn what to do with the alignment check, and get through the whole process more quickly, I'll be OK.

Thanks for the help.
 

rcflyinghokie

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After doing the P52, I skipped the Alignment Check, because I don't really understand what I'm doing with this procedure and it's been eating up a lot of time. I went right to the V41N91 star check, beginning at about 5:19.
Basically the alignment check you are checking the auto and manual abilities of the sextant/telescope. In a nutshell, you are doing a P52 option 3 three times with manual star selections in which you manually maneuver the spacecraft to have the star and then verify it with the auto driving of the optics.
By getting to the star check earlier than I have been, my SXTS star (15) was in view. But while it was close to the SCT cross-hairs, it was not close enough. It was not in view in the SXT. This may be because I'm omitting the Alignment Check?
What do you mean by not close enough? If it is visible in the sextant its a good star check. The further you are from your burn time though the further away it can be from "center"
 

Wedge313

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First off, I appreciate you taking the time to help me work through this...

What do you mean by not close enough? If it is visible in the sextant its a good star check.
See screenshots. It's near the SCT crosshairs, but not close enough to been seen in the SXT.

make sure V48 has the right trim angles because they used in the REFSMMAT calculation,
Another learning opportunity for me.... before the PAD and P30 target load, the DAP is set at 21111, 11111 and the gimbal angles are -00135 and +00133.

The PAD gimbal angles are +00105 and -00023.

I tried this a couple of ways. First I left the V48 gimbal angles as they were, then ran through the P30, started P40 then exited with P00, ran P52 opt 1, V49 to the burn attitude (PAD 000/356/001) then V41N91. The SXTS looked like the photos.

The second time, I did the uplink, then changed the V48 to 21102, 01111 and changed the gimbals to the PAD angles +00105 and -00023. Then I ran P30, started P40 exiting with P00, P52 opt 1, then V49 to the burn attitude. The SXTS star looked slightly closer to the center of the SCT but still not visible in the SXT.

I'm doing these about 50 minutes before the burn, but even if I wait until 30 minutes before the burn the star is not visible in the SXT.

In a nutshell, you are doing a P52 option 3 three times with manual star selections in which you manually maneuver the spacecraft to have the star and then verify it with the auto driving of the optics.
"manually maneuver" to what? Do I need to have a star centered in the SCT crosshairs? Or just visible in the SCT? After I choose a star and manually enter it, what maneuvering do I do before I choose and manually enter the second star? When I start over with the V32, do I maneuver again to a totally different set of stars? We go through this three times, and this confusion on my part is why I'm eating up so much time.

And will this alignment check correct what looks like an incorrect alignment?

Apologies for dragging this out, but I'd like to try and understand what I'm doing wrong.
 

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