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Project Apollo - NASSP 6.4.3 released!
http://nassp.sf.net
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| | |-+  P52 IMU Realign Apollo DSKY Error
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Author Topic: P52 IMU Realign Apollo DSKY Error  (Read 3550 times)
dseagrav
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« Reply #15 on: January 05, 2017, 07:44:55 AM »

It would be zeroed in real life; Cores are magnetic and have negative state (all zeroes, or all ones if the memory signals are active low instead of high) if never set. By the time the AGC is mounted in a spacecraft the memory will have been initialized to zero during or after the acceptance tests.

You may be thinking of bit rot; That's a different phenomenon (and we don't simulate it)
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indy91
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« Reply #16 on: January 05, 2017, 07:51:10 AM »

Just tried a P52 option 1 with a Desired REFSMMAT of all zeros. It lets me progress through the new IMU angles all the way until the first star is automatically chosen and then it throws me out of P52 with a 1301 program alarm, which is: "Arcsin or arccos input is greater than one". That alarm makes sense, if the REFSMMAT is so bad then some of the calculations with the REFSMMAT will break down. The actual REFSMMAT is still intact in the scenario, so it certainly looks like that this is what happened to @Puma.
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Puma
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« Reply #17 on: January 05, 2017, 09:31:01 AM »

Thank you for your quick response, could you explain Desired REFSMMAT and what I should do with it? in other hands can I fix my current mission by doing a P51? Thanks.
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indy91
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« Reply #18 on: January 05, 2017, 09:57:16 AM »

Sure. The actual REFSMMAT of course defines an orientation with respect to the stars, so that with a current IMU alignment the AGC is able to find stars and celestial bodies. It is chosen so that e.g. for launch the pitch angle of the IMU is 90.  Throughout a mission this orientation is changed sometimes. It might be chosen so that during a burn the IMU angles are 0, 0, 0. In the process of changing this orientation, changing the REFSMMAT, you don't want to loose your alignment. So the REFSMMAT that you want to use after an alignment, the so called "Desired REFSMMAT", is just the new REFSMMAT stored in a temporary location until the P52 option 1 is done. At that time the Desired REFSMMAT is copied into the memory location of the actual REFSMMAT.

The AGC itself can calculate a Desired REFSMMAT. You would give the AGC the burn parameters in P30, then go into P40 for a short time and then do a P52 option 1. This might sound complicated, but you will do that a few times later in the Apollo 7 mission. The other source of a Desired REFSMMAT is a ground uplink. In this case the ground has done some calculations for the REFSMMAT that the AGC can't do. This uplink is the one you missed at 4:45h GET. And trying a P52 option 1 without a Desired REFSMMAT causes bad things to happen, as you have noticed.

A few posts above I already posted a fixed scenario for you. If you really want to try to fix it yourself, then you just have to do the steps I did. The uplink was still stored in the scenario, so I first accepted the uplink. I described the procedure in the post with the fixed scenario. Then I did a P51 to get an initial alignment and then I did a P52 option 1 to align the IMU to the uplinked REFSMMAT.
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Puma
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« Reply #19 on: January 05, 2017, 10:34:30 AM »

all those thing should be included in the checklist? is this really realistic? I mean does the astronauts this all this in that way? for me it looks more as a flying controller simulator than a space flight simulator, maybe I am wrong. Have you ever tried this:

https://www.indiegogo.com/projects/go-for-launch-mercury-vr-educational#/

you may download the free demo here:

https://dl.orangedox.com/r9vGCk0tbGhIEMTSDV

Is there any chance that Orbiter could be something like that?
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meik84
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« Reply #20 on: January 05, 2017, 01:34:36 PM »

Quote
all those thing should be included in the checklist? is this really realistic?
It should be in the word checklist at least, but I don't think we have to include a contingency/recovery procedure (which it is, IMHO) in checklist MFD.
Quote
I mean does the astronauts this all this in that way?
The CMC runs the original software, so yes, they did. And yes, they sometimes messed up with the CMC, too. Jim Lovell caused an average 'Ooops!' on Apollo 8 (which almost got him an unscheduled EVA -Frank Borman intended to throw him out of the window for that) and had to do the whole P51/P52 smash, just like you.
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for me it looks more as a flying controller simulator than a space flight simulator
*shrug* Spaceflight is the culmination of engineering, so don't expect too much action... Wink Many Apollo astronauts held degrees in mechanical, electrical or aeronautical engineering. Buzz Aldrin held the nickname 'Dr. Rendezvous' because he described the mathwork behind orbital rendezvous in his thesis. Doesn't sound like a steel-eyed, cold-blooded superhero, huh?
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jalexb88
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« Reply #21 on: January 05, 2017, 02:13:56 PM »

all those thing should be included in the checklist? is this really realistic? I mean does the astronauts this all this in that way? for me it looks more as a flying controller simulator than a space flight simulator, maybe I am wrong. Have you ever tried this:

https://www.indiegogo.com/projects/go-for-launch-mercury-vr-educational#/

you may download the free demo here:

https://dl.orangedox.com/r9vGCk0tbGhIEMTSDV

Is there any chance that Orbiter could be something like that?

I don't know for sure about that program but a lot of those other simulators don't use a real-time physics engine so it's more of a "scripted" experience which makes it easy to only simulate the "astronauts perspective" part. In orbiter/NASSP however, we must simulate the ground support portion because nothing is scripted, we are using real Newtonian physics and if you screw up your maneuver or alignment by a fraction you will miss the target by a large amount. in NASSP we must use either the MCC simulation (PADs and uplinks with the MCC menu) or using an MFD such as RTCC MFD to accomplish what the people on the ground did. Space flight is not a one-man affair like flying an airplane, its a whole team of people most of which are on the ground, the "flight controllers". In an ultra-realistic sim like orbiter, this must be simulated.
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