Question about Apollo 8 P22

Zuppermati

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Hello everyone

I'm currently at T+76:05:00 in Apollo 8, when you're supposed to perform a P22 on site B-1. However I'm really struggling to understand what am I supposed to do (or better, to understand if I'm doing it right).

Basically: at the time of P22 you're supposed to roll to ORDEAL roll = 0, pitch = 5 and yaw = 0. By setting the trunnion to 10 degrees as required, you are basically pointing at the moon horizon, correct? At the same time, you are required by the checklist to keep a pitch rate so that you are always pointing to the horizon, correct? (by the way: is there any noun for verb 16 which allows you to display the exact ORDEAL angles?)

Ok: at this point, after the whole P22 initialization, the checklist mfd tells me to "Identify the landing site B-1 at acquisition time". I suppose it means to wait till the site appears from the horizon (which can be seen by using the display function). Correct? Now what puzzles me is the next point of the checklist: "Evaluate lighting between landing site and terminator": just what on earth am I supposed to do?

Anyway: if I skip it, the next step is to go OPT MODE - CMC and hit PRO: at this point, from what I get, the optics should start tracking the site and the checklist tells me to "Evaluate auto-optics tracking of the landing site B-1". The issue is that I don't know if it's doing a good job or not: from what you can see in this image its not perfectly centered (notice that I zoomed a lot on that image), so I don't know how to evaluate it.

At the same time I'm puzzled about the fact that according to the official CMP checklist, at page 17, it talks about performing a serie of MARKs when v51 is shown but both dsky and the checklist mfd doesn't mention it anywhere.

So the thing is: am I doing this right? Regards.
 

indy91

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I think at 76:05 they didn't do a full P22 yet, but just checked the landmark, if it is easy to find, if the lighting is good etc. Only one orbit later didn't the really start with the landmark tracking.
 

Zuppermati

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Hi, sorry for the late reply but I was actually trying to understand the proper P22 procedure that you have to perform "one orbit later".
Just to check if I got the standard procedure right: the checklist wants you to point to ORDEAL R = 0, P = 5, Y = 0 and start an orbital pitch rate to keep the ORDEAL attitude. After the initial P22 setup, you have to point the trunnion to 10 degrees upward (this time it doesn't point to the exact horizon) and wait for the landmark to appear. In my save file, it shows up at around T+77:28:00. Then i have to wait for a couple of seconds (from what I understand, you shouldn't do this when the landmark is at the horizon) and pitch down in order to archive a pitch rate of 0.3 deg/sec (I don't understand the purpose of this maneuver: is this to extend the time the landmark is visible?).
Now: from what I got, I have to use the wasd keys to point the optics to the landmark and perform 5 MARK with an interval of 20 seconds between each other, correct? With this procedure I got relatively low deltas, so I guess it's right but I might be missing something.

PS: there is nothing wrong with performing a ground controlled state vector update before P22, right?
 

indy91

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Yeah that procedure is correct. You put the trunnion to something higher than 0° to have a better field of view around the landmark once it comes up. The pitch rate starts at "acquisition", which is a point defined when the CSM is at 35° elevation angle from the landmark, so not when the CSM comes over the horizon as seen from the landmark (that would be 0° elevation angle).

Here a picture from the Apollo 11 Flight Plan that illustrates the procedure: https://history.nasa.gov/afj/ap11fj/a11fp/a11-fp-3-064a.jpg That time is T2 on the P22 PADs.

The same flight plan also contains a profile for the CSM alone, without the 0.3°/s pitch rate, so just staying in orb rate. So there isn't one correct technique. The advantage with the pitch rate is as you say, the landmark is longer in the field of view of the sextant. But also, the rate at which the landmark moves through the field of view is smaller during the middle part of the marking sequence. That makes it easier to keep the sextant on the landmark.

Even spacing of the marks helps with the accuracy of the state vector calculated from the marks. And it's no problem uplinking an accurate state vector before the P22.
 

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Hi, sorry again for the 1 month delay between answers. I was actually trying to perform all the P22s required before going back to you but my personal life got in the way. Anyway I wanted to thank you. I finished everything and everything went fine.

PS: by the way, I noticed that the MFD checklist doesn't mention a "fail to reject" procedure in the event of delta values too high, unlike P52 or P23. Does that mean that any delta value is fine with P22? Cause I also noticed that I received alternatively high and low deltas, ranging from 00100 to all zeroes depending on the landmark
 

indy91

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Not really sure, the mission techniques document even suggest that DR and DV would always be 0, which is only the case if the W-Matrix isn't used. Not sure why they would do that, but in any case it would mean to accept all P22 sightings no matter how bad they were. They got a new state vector uplink on almost every revolution anyway, so they wouldn't have used a broken onboard state vector for long.
 

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Hello

I have some issues on the attached quicksave. (Orbiter 2010 P1 - NASSP 7)

Around GET 78:00:00 my AGC hangs, it´s on P00 and the COMP ACVY light comes on, and remains on. 10 seconds before 78:05:00 I do a Verb 96 as I was reading this thread, and everything seems to return to normality.

The main problem I have, is that when I run P22 I think that I do all the steps correctly; I am on Ordeal R0, P5, Y0, Trunnion to 35º, load the landmark code 10001, optics to CMC, speed to HIGH, Coupling to resolved. When B1 appears on the center of the telescope, I press PRO, but I get a 404 program alarm, instead of F06 92.

Will try to make a video about this, but if someone could enlighten me on this issues, it would be greatly appreciated.
 

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STS

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Lots if info to read on that thread!

Verb 93 didn´t fix my issue, but as stated there, performing a CSM state vector update through RTCC MFD fixed my AGC and my P22.

The only question that I have now is, as my AGC locks up a short time before the 421 alarms, at a random moment

...Around GET 78:00:00 my AGC hangs, it´s on P00 and the COMP ACVY light comes on, and remains on...

and to solve it I have to do the V96 to be able to process the state vector:

Is there a way for me to predict that my AGC is going to have this behaviour and I should uplink a new state vector? (I am thinking than on real life I would be called by Houston, as GUIDO would see something weird, but MCC is not so smart on this simulation...)
 

indy91

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Ah NASSP 7, haven't tried you in a while...

Whenever I suspect a state vector related problem I first do a check with P21 if the AGC can find the correct latitude, longitude and altitude. A lot of things have to come together in the AGC for that to work accurately: AGC clock, time of launch set correctly, state vector being accurate etc.

Latitude and longitude seem a bit off, but the altitude is really off (22NM, unlikely in a 60NM circular orbit...). A check on the apoapsis and periapsis heights with V82 reveal that the state vector must be really bad, 82.6NM x -785.3NM (yes, that's a minus). That's really no basis to start a P22 with, so I would suggest uplinking a new state vector with the PAMFD. Not sure how that happened though, the scenario is before the first P22, right? The orbit seems accurate, nice and circular, so LOI-2 must have been good.

Time of liftoff (TEPHEM) and AGC clock seem accurate, so no issue there. Using the landmark code 10001 uses the landing site vector stored in the memory of the AGC, so there is always a potential issue there, but I checked in your scenario and it still has the same values as in the prelaunch scenario, so everything is fine there.

Using V96 is always only a temporary measure. It stops the AGC from propagating its state vector. If the state vector is really bad or very old then this can lock up the AGC (COMP ACTY light) for a long time or even forever, so V96 at least let's you use the AGC again. But it doesn't fix the issue of a problematic state vector, so you will usually need a new one uplinked.

In the real MCC they had a display called the vector compare display, where they could compare various state vectors to each other, like CMC CSM state vector compared to the current best estimate from ground station tracking. I have implemented that display in the RTCC MFD, here an older picture:


But it will not make its way to NASSP 7 and it's still quite experimental. I was just working on it yesterday actually. That display can tell you very quickly how good or bad a state vector is. The first column has various orbital parameters and the other columns then have the difference to the base vector in the first column.
 

STS

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Latitude and longitude seem a bit off, but the altitude is really off (22NM, unlikely in a 60NM circular orbit...). A check on the apoapsis and periapsis heights with V82 reveal that the state vector must be really bad, 82.6NM x -785.3NM (yes, that's a minus). That's really no basis to start a P22 with, so I would suggest uplinking a new state vector with the PAMFD. Not sure how that happened though, the scenario is before the first P22, right? The orbit seems accurate, nice and circular, so LOI-2 must have been good.
This scenario is after the first P22, wich I think went good. Both LOI-1 and LOI-2 went good.

I´ll do V82 before each P22, to check if my state vector is correct, and if it´s not I´ll uplink a new state vector from RTCC MFD, as that fixes my problem.

Very promising displays you show there for Nassp 8! :cheers:
 
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