Apollo 9: LM P20 After Phase Burn V80E OprErr?

[Wedge313]

Hi,

Just completed the phase burn (thanks to a four-year old thread with input from Indy). Starting the LM P20, checklist has us V95E to inhibit updating the SV. Then we start P20, and manually maneuver to the tracking attitude.

After the maneuver (I can see the CSM out the window) we hit PRO, followed by a V80E to start updating the SV. When I do this V80E, I get an OPR ERR light.

I think I'm following the checklist correctly. Any reason I'm getting an OPR ERR here?

Thanks.

 

[rcflyinghokie]

Hmmm that sounds correct on first read. You ENTER on the N18, manually maneuver, then PRO to exit the N19 then V80. You don't still have the LR spurious test running by accident do you? Try keying a V79 before your V95 and see if that works. If not, would you mind posting a save?

EDIT: One other thing, is your RR up and in LGC?

 

[Wedge313]

Tried V79 before V95, didn't seem to improve the situation. Not sure what I've done wrong here.

Here's a save at the PAMFD checklist "Phasing +4m" point (I'm about 9 minutes after phasing, I'm running a bit behind but I don't think that should matter here?).

Also just a tip, when you arent doing a burn, configure your auto RCS switches to match your DAP (A/C or B/D roll) this will let you use SCS without using all 4 roll quads and using more fuel and having larger rates.

Also, thanks for the tip, but I just haven't gotten around to doing this yet. I'm too busy messing up my Docked DPS and Phasing burns!

 

[rcflyinghokie]

Looks like you did something screwy when you did a V84 previously to update the SEP burn, or something with the RR checkout (extra PRO by accident maybe) causing R32 bit to be no longer set. Maybe entered it wrong, omitted it, or forgot a V80. In any case you can re enable this by making sure you are in P00, doing another V84 for a time in the past with zero dV's. Then do a V80 and you should have no light. Then do a V95 and resume the procedure from there.

 

[Wedge313]

I'd like to get this correct. I think my problems start right after the SEP burn. When I start the CSM P20 and run through the steps, I get to the point where the checklist says, "When attitude OK". What is "OK"? Should the LM be centered in the optics at this point?

 

[rcflyinghokie]

I'd like to get this correct. I think my problems start right after the SEP burn. When I start the CSM P20 and run through the steps, I get to the point where the checklist says, "When attitude OK". What is "OK"? Should the LM be centered in the optics at this point?

Basically that just means when your auto maneuver is complete. It says "attitude OK" because since the vehicles are moving, the attitude can actually change from the time you begin maneuvering to the first completion.

The LM will likely not be centered in the optics because the optics need to drive first.

I wrote those steps as kind of an abridged version since A) we don't have the CSM solo procedures for 9 and B) They are as time permits.

I'd be happy to explain the full version of what you can/should do and why (if you have the time, of course)

 

[Wedge313]

I'd be happy to explain the full version of what you can/should do and why (if you have the time, of course)

Thank you for the offer. I want to get into the CSM side of this exercise, but for now I'm still trying to figure out where I'm going wrong with the LM procedures.

You were correct with your V84 call, when I input a V84 before starting the LM P20 I don't get the OPR ERR light. But I'm getting a slew of problems with the P20 and P34 programs, lots of error messages and unexpected DSKY displays. I'm currently re-doing the scenario from the point just before I undocked, and working forward slowly trying to follow along with the copy of the Apollo 9 LM G&C checklist. Hopefully I'll find my error this time through (I'm wondering if I when I ran V84 I got the dV sign wrong, - vs +?). I'll hopefully get to it tomorrow AM.

Meanwhile, I don't suppose there's a copy of the Apollo 9 LM AOH, or an AOH that reflects the procedures with the Apollo 9 software?

Thanks for the help!

 

[rcflyinghokie]

Thank you for the offer. I want to get into the CSM side of this exercise, but for now I'm still trying to figure out where I'm going wrong with the LM procedures.

You were correct with your V84 call, when I input a V84 before starting the LM P20 I don't get the OPR ERR light. But I'm getting a slew of problems with the P20 and P34 programs, lots of error messages and unexpected DSKY displays. I'm currently re-doing the scenario from the point just before I undocked, and working forward slowly trying to follow along with the copy of the Apollo 9 LM G&C checklist. Hopefully I'll find my error this time through (I'm wondering if I when I ran V84 I got the dV sign wrong, - vs +?). I'll hopefully get to it tomorrow AM.

Meanwhile, I don't suppose there's a copy of the Apollo 9 LM AOH, or an AOH that reflects the procedures with the Apollo 9 software?

Thanks for the help!

What kind of errors are you getting in P34? N49s? 525s? If so you are likely correct on a V84 issue or you have a side lobe lock on.

You have the Apollo 9 G&N dictionary that is pretty much the software procedures. What procedures were you looking for?

 

[Wedge313]

What kind of errors are you getting in P34? N49s? 525s? If so you are likely correct on a V84 issue or you have a side lobe lock on.

You have the Apollo 9 G&N dictionary that is pretty much the software procedures. What procedures were you looking for?

I think all the problems related to P20. After starting P34 I kept getting 525 alarms (SV/RR LOS > 3 deg). F 06 49 would also pop up, and I don't know what "delta SV" is (or should be), as well as what delta R or delta V should be. Should I accept? Reject? Recycle? An occasional F 06 05 displayed. Lots of stuff. I was hoping the expanded description in an AOH might help me out. But it all tells me I was way off somewhere, which is why I abandoned that attempt and went back to the undocking and started over.

On that note, I just finished the phasing burn. Just wanted to check that I did this correctly...

At phase TIG - 2 min when the checklist says "Trim AGS errors to 0", I rolled the LM to 000, and tweaked the pitch and yaw to center the FDAI needles. At this point the CSM was centered in the boresight just before ignition, FDAI RPY 000,285,000, slightly different than the PAD pitch of 283. Does that orientation sound correct?

And then starting P76 in the CSM, the checklist asks to enter "desired" dVs and TIG. Do we enter the LM phasing burn dVs and TIG?

Thanks

 

[indy91]

I think all the problems related to P20. After starting P34 I kept getting 525 alarms (SV/RR LOS > 3 deg). F 06 49 would also pop up, and I don't know what "delta SV" is (or should be), as well as what delta R or delta V should be. Should I accept? Reject? Recycle? An occasional F 06 05 displayed. Lots of stuff. I was hoping the expanded description in an AOH might help me out. But it all tells me I was way off somewhere, which is why I abandoned that attempt and went back to the undocking and started over.

"SV/RR LOS > 3 deg" means that the direction to the CSM as the LGC knows it differs by more than 3 degrees than the direction that the RR is pointing to. So either LGC or RR is wrong, in the LGC it would be the state vector, with the RR it would be a side lobe lock-on. Delta SV means, when the LGC takes a mark using RR range and range rate data, the state vector is going to be updated in the LGC by a certain amount. If that update exceeds a threshold (5000 ft or 5 ft/s) it does not automatically incorporates the RR data but shows you that amount that the state vector is going to be updated by (N49, units are 0.1 NM and 0.1 ft/s). So it then gives you a choice for the update. If the update is too high then it could be a bad mark, or your initial state vectors are just quite inaccurate.

I've always felt that the Apollo 9 rendezvous stands or falls with the undocking. They didn't run P47 for undocking, but undocking does cause a DV on both CSM or LM. So it is very important that after undocking you fire the thrusters to have station keeping at the desired distance, I think 50 ft or so. The state vectors in CMC and LGC for CSM and LM are identical until you do the V84 for the CSM sep maneuver. If you just let the CSM and LM drift apart after undocking you are starting off with a not insignificant state vector difference, that could easily cause your P20 issues.

On that note, I just finished the phasing burn. Just wanted to check that I did this correctly...

At phase TIG - 2 min when the checklist says "Trim AGS errors to 0", I rolled the LM to 000, and tweaked the pitch and yaw to center the FDAI needles. At this point the CSM was centered in the boresight just before ignition, FDAI RPY 000,285,000, slightly different than the PAD pitch of 283. Does that orientation sound correct?

Yeah, good enough. The AGS isn't a very clever system. If you give it automatic attitude control for a burn and your current attitude is far away from the burn attitude, you get really high attitude rates. So what you want to do there is to get to the burn attitude manually (that's the "Trim AGS errors to 0") and only then give the AGS automatic control, so that it doesn't have do a big maneuver.

And then starting P76 in the CSM, the checklist asks to enter "desired" dVs and TIG. Do we enter the LM phasing burn dVs and TIG?

Yes, P76 (and V84 in the LGC, which does the same thing) is how you tell your computer that the other vehicle has done a maneuver. So you enter the DV and TIG of the maneuver. If you want to get fancy, instead of using the TIG from the PAD you can see that e.g. the burn took 26 seconds so you add half of that to the TIG. P76/V84 "simulate" the burn as an instant velocity change, so using a TIG of halfway into the burn gives you a bit more accurate state vector. But it's not strictly required, after one or two marks with sextant or RR this error would already be cancelled out. And the CSM sep maneuver is short enough that you should just use the actual TIG and not do any math there haha.

 

[Wedge313]

I've always felt that the Apollo 9 rendezvous stands or falls with the undocking. They didn't run P47 for undocking, but undocking does cause a DV on both CSM or LM. So it is very important that after undocking you fire the thrusters to have station keeping at the desired distance, I think 50 ft or so. The state vectors in CMC and LGC for CSM and LM are identical until you do the V84 for the CSM sep maneuver. If you just let the CSM and LM drift apart after undocking you are starting off with a not insignificant state vector difference, that could easily cause your P20 issues.

My first attempt this may have come into play, I know I had some drift going on between the CSM and LM. This time through the scenario after the undocking I worked hard to get the CSM and LM station keeping as close to stable as I could. As you said, without V47 I don't know which vehicle was drifting the most (probably both, action/reaction etc.), but I started by zeroing out the LM's drift away from the CSM about 50 ft. away, then fine-tuned it with the CSM, back and forth until I had them an estimated 50 ft. apart, then got the LM facing the CSM, and both vessels "frozen" relative to each other. So hopefully the SV's are pretty close before the SEP burn.

And after the phasing, I've started P76 in the CSM, and the optics have the LM in the SXT, it's searching a little back and forth but the LM stays in the SXT so the CSM seems to know where the LM is. So up to this point this attempt seems to be going better.

I'll get a fresh pot of coffee going tomorrow morning and dive into the LM P20, hopefully it goes a little more smoothly.

Thanks for the explanation of the P20 errors.

 

[Wedge313]

OK, things proceeding much better, I'm now at a point about 10 minutes before insertion. The P20/P34 all went well this time, no errors.

A couple of questions.

What exactly was the whole TPI0 about? Just an exercise to test P20 and P34?

During the whole process, I kept manually pitching the LM to orient toward the CSM. One time I let it get away a bit and got a F 50 18 message, so the LGC was telling me to maneuver. Why are we doing this in ATT HOLD? would the LM track the CSM if we were in AUTO?

Thanks.

 

[rcflyinghokie]

What exactly was the whole TPI0 about? Just an exercise to test P20 and P34?

That was part of it, this was called the "mini football" maneuver. This orbit placed the LM in a position to return to the CSM easily and in one orbit should something go wrong in the LM. It also, as you mentioned, allowed the crew to test P20 and P34 before committing to a full rendezvous sequence.

During the whole process, I kept manually pitching the LM to orient toward the CSM. One time I let it get away a bit and got a F 50 18 message, so the LGC was telling me to maneuver. Why are we doing this in ATT HOLD? would the LM track the CSM if we were in AUTO?

Sundance does not automatically orient the spacecraft to the CSM after the initial N18 maneuver like Luminary. So if you drift beyond a certain LOS angle (I cannot remember the threshold offhand) it will give you a new N18 angle to orient to. The reason you do it in ATT HOLD and min impulse is so you keep the LM manually oriented to boresight the CM +Z and simultaneously null the RR error needles.

 

[Wedge313]

Beginning P32, entering the TPI TIG. The checklist says "Load TIG of TPI (With +3 Min Time Bias)". My PAD TPI TIG is 97 47 28.72. Does that already include the bias? Or do I add 3 minutes to the PAD value and enter 97 50 28.72? The LGC is going to calculate its own TPI TIG later anyway, isn't it?

And following along reading the Apollo Flight Journal... what is the DFI? They keep turning the DFI power on and off for these burns.

Thanks

 

[rcflyinghokie]

Beginning P32, entering the TPI TIG. The checklist says "Load TIG of TPI (With +3 Min Time Bias)". My PAD TPI TIG is 97 47 28.72. Does that already include the bias? Or do I add 3 minutes to the PAD value and enter 97 50 28.72? The LGC is going to calculate its own TPI TIG later anyway, isn't it?

Correct you are adding 3 minutes to that initial time to correct for the conic calculations used by the LGC here. This time is used to compute CSI. The LGC will compute a new TPI time of course later based on CSI/CDH but this is to give the initial starting point.

And following along reading the Apollo Flight Journal... what is the DFI? They keep turning the DFI power on and off for these burns.

So LM-3 was equipped with an array of recorders for testing including R&D instrumentation and the Development Flight Instrumentation (DFI) package. This allowed recording and transmitting of a bunch of telemetry values not included in the normal telemetry array to further prove the flight readiness of the LM. This was only in LM-3 and was not included in subsequent LM's which is why you don't see the panel switches for it in our LM.

 

[Wedge313]

Slowly working my way through the rendezvous.

On both the CSI P32 and CDH P33 checklists there's a line that reads "If Ydot > 2fps, insert negative Ydot in R2". My Ydot worked out as 0000.6. What would I enter here?

The first time I'm asked to enter my CDH time was before I received the PAD. How would I determine that? I took the CSI time (96 09 00), added the calculated CSI/CDH dT (41+18), and then added the bias 1+45 to get a CDH time of 96 52 03.

Shortly after I received the CDH update PAD, showing a CDH TIG of 96 53 40.07, about 1 min 37 sec different than my calculated CDH. Also, my calculated dVZ was -00099, the PAD dVZ is -00022.

Now, after the CDH final comp, I need to enter the CDH TIG. Should I go with my calculated TIG or the PAD TIG? Same question for the dVZ, use the calculated or PAD value?

Thanks.

 

[rcflyinghokie]

On both the CSI P32 and CDH P33 checklists there's a line that reads "If Ydot > 2fps, insert negative Ydot in R2". My Ydot worked out as 0000.6. What would I enter here?

This is the out of plane correction. If you are computing Ydot in PGNS, you have .6 fps, so you can omit entering the negative Ydot into your computation.

The first time I'm asked to enter my CDH time was before I received the PAD. How would I determine that? I took the CSI time (96 09 00), added the calculated CSI/CDH dT (41+18), and then added the bias 1+45 to get a CDH time of 96 52 03.

For CDH you want to use what the LGC provides, the pad is just a ground solution but you want to use the LGC solution.

Now, after the CDH final comp, I need to enter the CDH TIG. Should I go with my calculated TIG or the PAD TIG? Same question for the dVZ, use the calculated or PAD value?

Same as CSI and TPI, you leave the LGC values in there and dont type anything new in your time or dVs.

 

[indy91]

The current MCC solution for the CDH burn uses a time of ignition that gets calculated differently in the RTCC than in the LGC. That kind of happened on the actual mission, too, so mission control took the LGC time for the CDH burn, re-calculated the burn for that time and that became the CDH PAD, so exactly identical TIG as the LGC. There will be a fairly big update to the Apollo 9 MCC in the near future and I will just pull that CDH time from the LGC memory and use it as TIG. But only if it is somewhat close to the RTCC calculated TIG, otherwise the CDH PAD would be a failure as a backup solution, because it needs to work right even if you have screwed up the LGC calculations.

For the LGC time, when you first start P33 it already has the CDH time that got calculated in P32. So you don't need to add any CSI/CDH DT. P33 already shows you that exact time. So you only need to add the 1m45s bias that is caused by P32/P33 not working quite right in Earth orbit (conic calculations where integrated trajectories would be needed for accurate results).