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Author Topic: Apollo 7 vAGC SPS Burns  (Read 5493 times)
Phixit
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« on: January 09, 2010, 11:59:23 PM »

All,

I'm new to NASSP, but I'm having a blast with it. I'm working through Apollo 7 in vAGC right now, but have hit a snag. I've set up to do the SPS burn and it starts on schedule, but the CSM quickly goes out of control. Basically it starts to tumble and the rcs can't compensate. I have attached the scenario I'm working with (saved a little over a minute before the burn).

I'm not sure if this is part of it, but when I do V37E 40E to have the AGC align the CSM it does not move, but almost immediately begins flashing "V50 N18". However the FDAI is lined up with the yellow needles.

Thanks for the help and thank you very much for the sim.  Happy

-Rob

* apollo_7_sps_issues.scn (76.41 KB - downloaded 90 times.)
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pattersoncr
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« Reply #1 on: January 10, 2010, 07:48:15 AM »

What checklist are you following?
Are the gimbal motors running?
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Phixit
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« Reply #2 on: January 10, 2010, 08:00:17 AM »

What checklist are you following?
Are the gimbal motors running?

Thanks for the reply. I'm using the latest cvs build and the excel checklist that came with it: "Doc\Project Apollo - NASSP\Flightplans\Apollo 8\Apollo 8 Flightplan vAGC.xls". The gimbal motors are running, unless there is something I have to do besides flip them to start momentarily and then let to return to center.
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Gunner_CAF
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« Reply #3 on: January 10, 2010, 11:22:53 AM »

Your running A7 with A8 checklist?  You should have a checklist for both A7 and A8 in the Flightplan folder.  The missions are quite different and the procedures in the tabs are also different.  I just did a TLI burn for A8 last night and I have been comparing the tabs in the two checklists.

Gunner
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Phixit
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« Reply #4 on: January 10, 2010, 11:53:06 AM »

Your running A7 with A8 checklist?  You should have a checklist for both A7 and A8 in the Flightplan folder.  The missions are quite different and the procedures in the tabs are also different.  I just did a TLI burn for A8 last night and I have been comparing the tabs in the two checklists.

Gunner

Sorry I mistyped in my last post, I am using an Apollo 7 checklist: "Doc\Project Apollo - NASSP\Flightplans\Apollo 7\Apollo 7 Flightplan vAGC.xls". I guess I wrote that last post way too early in the morning. So I think I'm using the right one. Any ideas?
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Tschachim
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« Reply #5 on: January 10, 2010, 12:18:11 PM »

Could you provide a scenario saved before you start P40? I can't tell if the orientation of the spacecraft is wrong (and why), it's too short to the burn.

Cheers
Tschachim
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Gunner_CAF
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« Reply #6 on: January 10, 2010, 12:24:27 PM »

All,

I'm not sure if this is part of it, but when I do V37E 40E to have the AGC align the CSM it does not move, but almost immediately begins flashing "V50 N18". However the FDAI is lined up with the yellow needles.


Rob, you may be onto something here.  When you do P40, the CSM should start aligning to the attitude for the burn.  Most of the burns in A7 (except for burn 5) are short and you should be pointing mostly prograde, or retrograde.  When V59 N18 flashes, the angles displayed on the DSKY should match the Flight Director.  Unless you happen to be close to the correct attitude, it takes several minutes for the CSM to align and the DSKY flashes.

If the CSM is spinning out of control, it sounds like the gimbal motors may not be on.  The correction during the burn should be controlled by the gimbals, not the RCS.

I suggest backing up a bit and make sure your not missing anything in the checklist.


Gunner
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Phixit
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« Reply #7 on: January 10, 2010, 01:13:46 PM »

Thanks for the replies.

Could you provide a scenario saved before you start P40? I can't tell if the orientation of the spacecraft is wrong (and why), it's too short to the burn.
Found one, see attached. It is at about TIG -20:00 and I'm starting P40 around TIG -15:00, according to the checklist.

If the CSM is spinning out of control, it sounds like the gimbal motors may not be on.  The correction during the burn should be controlled by the gimbals, not the RCS.

I suggest backing up a bit and make sure your not missing anything in the checklist.

I'm pretty sure the gimbal motors are on, but I will start the SPS burn checklist again and see how it goes. One question before I go back through. When I activate the DAP (V48E) should I change line 1 if it does not read 10002? If I remember correctly it had a different number, but I didn't change it. (should of put that on my original post, but forgot)

I should be able to get to it tonight, I'll let you guys know. Thanks for the help. What is it with space simulators and great support communities?  Very Happy

* apollo_7_p40.scn (77.13 KB - downloaded 98 times.)
« Last Edit: January 10, 2010, 01:22:52 PM by Phixit » Logged
Gunner_CAF
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« Reply #8 on: January 10, 2010, 01:22:57 PM »

I just ran your scn file.  Wow, I see what you mean Happy

It looks to me like the your pointed in the wrong direction, the gimbal motors are trying to steer you in the right direction, but your initial attitude is too far off so it puts you into a spin.

From my flight data from A7, this first burn dVx was 20.3 ft/s, dVy and dVz were 0.  The DSKY is indicating a total change of 20.73 ft/s so that is close.  The problem is you are pointed down (twards earth) and I think you should be pointing more in the prograde position.  The SPS Gimbal indicators (Panel 1) are not centered so it looks like the gimbals are trying to correct for the attitude and this is what is causing the spin.

Everything else looks set correctly except for the dV setting on the EMS, this should be set at 20.7, not 207.0.  This isn't the problem with the spin.

My guess is it is something with the alignment when you do P40.

Good luck!

Gunner
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Tschachim
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« Reply #9 on: January 10, 2010, 06:31:32 PM »

One question before I go back through. When I activate the DAP (V48E) should I change line 1 if it does not read 10002? If I remember correctly it had a different number, but I didn't change it. (should of put that on my original post, but forgot)

Yes, your DAP isn't running. Change the "V48 line 1" to 11102, also you need to activate the DAP with V46E after that.

Cheers
Tschachim
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Phixit
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« Reply #10 on: January 10, 2010, 11:40:57 PM »

Yes, your DAP isn't running. Change the "V48 line 1" to 11102, also you need to activate the DAP with V46E after that.

Thanks, this worked! I went back through and when I activated the DAP I used this command and everything went to plan. 1st SPS burn down, now 7 more to go.  Very Happy

Everything else looks set correctly except for the dV setting on the EMS, this should be set at 20.7, not 207.0.  This isn't the problem with the spin.

Thanks, missed that the AGC displayed in 0.1 ft/sec intervals at that point. However I tried that this time around, set it to 31.8 (this time the AGC said 318.2). When the burn happen this number decreased past 0 to something around 300. However the third line of the AGC (velocity gained in fps) said 32 ft/s. Also the PeA and ApA after the burn agree with the predicted. So I think the burn did fine and the EMS just displayed it wrong. Not sure.

Anyway, thanks for all your help guys!  Very Happy
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Tschachim
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« Reply #11 on: January 11, 2010, 07:38:58 AM »

However I tried that this time around, set it to 31.8 (this time the AGC said 318.2). When the burn happen this number decreased past 0 to something around 300.

If your dV is 318.2 ft/s, you need to set the EMS to 318.2.  Happy
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Phixit
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« Reply #12 on: January 11, 2010, 08:11:02 AM »

If your dV is 318.2 ft/s, you need to set the EMS to 318.2.  Happy

My dV is actually 31.82 ft/s. I was talking about during P30, when you set the info for the burn. The AGC displays the total dV in 0.1 ft/sec. So it says 318.2 then, which should mean I enter 31.8 on the EMS correct? Does the EMS display ft/s or 0.1 ft/sec? Thanks.
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Tschachim
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« Reply #13 on: January 11, 2010, 08:21:57 AM »

My dV is actually 31.82 ft/s. I was talking about during P30, when you set the info for the burn. The AGC displays the total dV in 0.1 ft/sec. So it says 318.2 then, which should mean I enter 31.8 on the EMS correct? Does the EMS display ft/s or 0.1 ft/sec? Thanks.

The EMS displays 0.1 ft/s, it has a decimal point, so you need to set it to "31.8" if your dV is 31.82 ft/s.

The AGC displays 0.1 ft/s, too, but it has NO decimal point, so it cannot display something like "318.2". If your dV is 31.82 ft/s, the AGC will display "318".
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Phixit
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« Reply #14 on: January 11, 2010, 08:56:31 AM »

The EMS displays 0.1 ft/s, it has a decimal point, so you need to set it to "31.8" if your dV is 31.82 ft/s.

The AGC displays 0.1 ft/s, too, but it has NO decimal point, so it cannot display something like "318.2". If your dV is 31.82 ft/s, the AGC will display "318".

Okay, so if the AGC says 03182, that means I should set the EMS to 318.2?
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