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Apollo 7 Rendezvous Procedure
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abr35
Project Team Member
Full Member
Posts: 35
Apollo 7 Rendezvous Procedure
«
on:
June 15, 2011, 03:32:00 PM »
I saw elsewhere on the forum that there was trouble coming up with a procedure for the rendezvous with the S-IVB. Is this still the case? Because I think I've figured out a way to do the corrective combination and coelliptic burns using the EOCA and IMFD. First I just want to make sure I'm correct on the purpose of the maneuvers, as I understood them from the Apollo 7 Press Kit:
SPS Burn #1 (CCM) - Raise the CSM orbit to establish a central angle of +1.32 degrees one orbit later. Also the CSM should be end up in a position 8nm below the S-IVB. This maneuver was calculated by the ground.
SPS Burn #2 (CSI) - Lower the apogee, making both orbits concentric circles. The perigee and apogee of the CSM should be 8nm below the perigee and apogee of the S-IVB. delta-Height should be about zero after this burn and the central angle will slowly decrease. This maneuver was also calculated on the ground.
TPI - Place the CSM in a transfer orbit to the S-IVB. If everything was done correctly up until now, it should be a relatively small burn, with two opportunities for midcourse correction. It was calculated on board using P34.
If all this is correct, I'll post the procedure so people can give it a whirl and iron out the bugs. Otherwise it's back to the drawing board for the time being
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eddievhfan1984
Full Member
Posts: 231
Re: Apollo 7 Rendezvous Procedure
«
Reply #1 on:
June 15, 2011, 05:45:01 PM »
Do we have any MFDs available to Orbiter 2010 that can display such parameters and calculate a burn for it?
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abr35
Project Team Member
Full Member
Posts: 35
Re: Apollo 7 Rendezvous Procedure
«
Reply #2 on:
June 15, 2011, 07:52:52 PM »
Not that I'm aware of. Here's how I went about the rendezvous (
it works, but I'm not sure if it's accurate
):
Corrective Combination Burn:
The following is done an hour before the burn.
1) Open the SYNC ORBIT MFD and select AS-205-S4BSTG as your target. Press MOD until it displays all DLng. DLng is you're current phase (or central) angle.
2) Subtract DLng from the target central angle (+1.32). Watch you're signs here!
3) Now take the orbital period of the S-IVB (T in the Orbit MFD) and divide it by 360. This is how long it takes the S-IVB to travel one degree in it orbit.
4) Multiply the answers to numbers 2 and 3. This is you're orbital time to gain, if you add this number to you're current orbit time, you will have a central angle of
about +1.32 one orbit after the burn.
Here's the entire calculation:
x = +1.32 - DLng
y = T(S-IVB)/360
z = xy
T(CSM) + z = Target Orbital Period After NCC1
5) Now subtract 14.3km (roughly 8nm) from the PeA of the S-IVB. This is you're target PeA for the burn.
6) Open the EOCA spreadsheet and configure the MJD, state-vectors, and propellant.
7) For the burn type select 11 (Orbit Adjust + LPe)
LPe: LPe of S-IVB
PeA: S-IVB PeA - 14.3km
ApA: Adjust so the the "T ~" field is equal to the Target Orbital Period
Now you should be 1.32 degrees behind the S-IVB and 8nm below it after one orbit.
Press F9 to calculate the burn. Select a solution, load the P30 fields and execute.
Mid-Course:
The press kit mentions a possible MCC just after passing the apogee between SPS Burn 1 and Burn 2. I originally tried to avoid this maneuver because it was not performed,
but I've found that it really helps you arriving at the proper location for CSI.
1) Open IMFD Delta-Velocity program.
2) Adjust the TIG so that the burn take place near or after the apogee.
3) Adjust dVf so that PeA = S-IVB PeA - 14.3
4) Adjust dVo to place the perigee underneath the S-IVB's. (Unfortunately you have to eyeball this one with the Orbit MFD)
5) Continue to readjust dVf and dVo so that both PeA and LPe are as desired.
6) Use the Apollo MFD to upload the burn.
Note:
This part of the procedure is admittedly sloppy. It gets the job done very well, but I'd perfer to have some way to calculate this. That would make things much
easier on the Mission Control programmers.
Coelliptic Sequence Initiate:
This burn is very easy if everything has been done correctly up to this point. I'd like to come up with a way to correct for minor errors in the CCM and Mid-Course,
though.
1) Open IMFD Orbit Insert program.
2) Set Eccentricity to the S-IVB Ecc value.
3) Use the Apollo MFD to upload the burn.
This should cancel out any delta-H and
Terminal Phase Initiation:
Historically the astronauts ran P34 to calculate TPI. I've noticed the Transfer program of IMFD works as a reliable back-up though. Tangenial Tansfer also works, though
with less reliability (it some times spits numerous burn vectors at you in rapid succession). You can use the Rendezvous MFD for midcourse as opposed to P35. I'll work on
this some more though so we can have a precise procedure.
There you have it! It definitely gets you a nice clean rendezvous with the S-IVB. I'm not sure how historically correct it is but I believe it comes pretty close. I
practiced burns 1 and 2 in NASSP and ended up pretty much where I wanted to be. The lack of 100x time accel caused me to decide to perfect the whole procedure using AMSO
though, so I'm not sure how well P34 works on the transfer.
If anyone wants to test this procedure and report on their results that'd be great. If anyone has any changes or comments that'd be great too. This is not yet what I'd
consider a final draft. Also, I'd really like to minimize the guess work and include more calculations. That way there is the possibility of having MCC-H do this for us,
just like in reality.
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meik84
Project Team Member
Sr. Member
Posts: 299
Re: Apollo 7 Rendezvous Procedure
«
Reply #3 on:
June 16, 2011, 09:28:57 AM »
Cool!
That's easier than I thought. I'll give it a try soon, but I'll have to start from scratch -I threw away all my quicksaves for this reentry thing...
The idea behind the CCR is good, I didn't know that this EOCA sheet can do that.
The midcourse... hm. From what I read in the mission report, they underestimated the atmospheric influences, which led to a 4 mins earlier TPI (up to 12 mins later/earlier was tolerated). I guess we should be this "historical inaccurate" (and spare the midcourse), too.
Regarding the CSI: shouldn't it be enough to reach a orbit with CSM PeA/ApA = SIVB PeA/ApA - 14.3 km (incl. the central angle, of course)?
For the TPI: the real astronauts had to rely on the CMC for this, as tracking data wasn't available in this short of time (furthermore, something went wrong on the ground during the real Apollo 7 and Houston didn't even have telemetry during TPI). From what I've heard in the forum, P34/35 work very well. The only thing we need to find out is the right GET for TPI.
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abr35
Project Team Member
Full Member
Posts: 35
Re: Apollo 7 Rendezvous Procedure
«
Reply #4 on:
June 16, 2011, 11:46:27 AM »
Right now the only reason why I have the midcourse is that the EOCA come close to putting the perigee where we want it, but sometimes its too high or the LPe is slightly off. As far as I'm aware the EOCA is still a beta, so it's possible the LPe shift mode isn't fully developed yet. It seems as if it tries to put it in the right spot but it can be off, sometimes significantly and sometimes only slightly. This could be as simple as me miscopying state vectors, or the AGC leaving too high of a residual velocity, so we'll see how it goes in testing. The midcourse is in there to correct for this until there's a better fix.
For the CSI: That works too
Either method should be solid but yours probably leaves more room for error during the CCM which is always a good thing.
I was able to get a TPI GET using tangential transfer a few times. You just slew through the TEj until you get the lowest Dist at intercept. Unfortunately, the IMFD seems to get confused and gives me multiple solutions if I move the TEj too quickly. Probably has something to do with the proximity of the orbits.
So basically if we can refine the CCM and get a reliable way to calculate TPI GET we should be in business. I have a rendezvous scenario if you want it, but the entire rendezvous procedure will be one hour off. I learned the hard way the EOCA only allows burns 60+ minutes away.
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Tschachim
Project Apollo - NASSP
Administrator
Hero Member
Posts: 3687
nassp.sf.net
Re: Apollo 7 Rendezvous Procedure
«
Reply #5 on:
June 17, 2011, 09:55:55 AM »
Great job with the rendezvous here guys, you're really running the show!
I moved the thread to Development as this is no planning anymore, I hope you don't mind.
I have no clue about rendezvous yet, but I'd like to make a few comments in general:
Just as a reference there are a couple of threads on that subject:
"Possible help to developers-Apollo 7 RNDZ", including an interesting booklet link:
http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=2391.0
Posts in "Steps before Apollo 7":
http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=1456.msg18941#msg18941
"Apollo 7: Calculating the CSI Burn":
http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=2279.0
"Apollo 7: Calculating the Corrective Combination Burn":
http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=2276.0
Irnenginer wrote a little bit about that in the Apollo 7 wiki article:
http://nassp.sourceforge.net/wiki/Apollo_7
Reading that it looks like we should cover the 2 RCS phasing burns before the SPS burns, too?
I just cleaned up the article a little bit and delete the links to the obsolete wiki checklists. In case someone wants to write docu / tutorials about Apollo 7
, please use the article as a starting point or to link to detail articles about this mission and ignore the Quickstart Mode for now, we'll deal with that later.
I don't know of Christophe is still around here, he probably will kill me reading that, but I'd be happy if we can do all "ground calculations" with IMFD (and LTMFD for Moon stuff and ProjectApolloMFD for upload). I think this would be more convenient for the user as there's one navi tool only, which is usable in-game. If I understand all that correctly this isn't possible with IMFD yet, but Jarmo, the author of IMFD, was very helpful with stuff like that and did a lot of stuff in IMFD / LTMFD for us, so perhaps he might want to help here, too. If this is a good idea for all and given that I'm not the rendezvous guru here, it would be cool if you guys could contact Jarmo for that and ask for help, his email is here (or PM in the Orbiter forum):
http://koti.mbnet.fi/jarmonik/Orbiter.html
Of course, if someone wants to code the calculations by himself, that's fine, too and we should put that in ProjectApolloMFD directly then.
Thanks and Cheers
Tschachim
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meik84
Project Team Member
Sr. Member
Posts: 299
Re: Apollo 7 Rendezvous Procedure
«
Reply #6 on:
June 19, 2011, 04:17:15 PM »
Quote
Reading that it looks like we should cover the 2 RCS phasing burns before the SPS burns, too?
We could do that -but I don't think it's necessary. Both burns had the only purpose to bring distance between the CSM and the SIVB. Correction of plane misalignment etc. was done with the CCR.
As we talk about phasing: the EOCA is flawed somehow. I put in the right PeA and ApA, but what EOCA puts out is wrong: I get ApA/PeA which are up to 5 nm away from desired altitude when I burn with this data. This could also be the cause of the midcourse problems abr35 is talking about.
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eddievhfan1984
Full Member
Posts: 231
Re: Apollo 7 Rendezvous Procedure
«
Reply #7 on:
June 19, 2011, 06:30:58 PM »
Well, EOCA has variable accuracy, right? What are your EOCA configuration settings?
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meik84
Project Team Member
Sr. Member
Posts: 299
Re: Apollo 7 Rendezvous Procedure
«
Reply #8 on:
June 20, 2011, 04:15:09 AM »
Solution accuracy is set to 0 (high), if you mean that. Interestingly, EOCA predicts the apoapsis of my current orbit 5 nm to high, too
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abr35
Project Team Member
Full Member
Posts: 35
Re: Apollo 7 Rendezvous Procedure
«
Reply #9 on:
June 20, 2011, 08:52:01 AM »
I never picked up on that issue with the EOCA, but it is without a doubt why I had to do the mid-course. One quick question: do we plan on always using the MFDs to calculate maneuvers? Or will the "spacecraft" (as in the Orbiter vessel) be doing that one day? Because I was thinking: if Jarmo gets the rendezvous stuff into the LTMFD, it'd become like an Apollo Guidance MFD. Then we have our required MFD count down to one, which in and of it's self is a big step. From there, if we really want to be ambitious, we can try to get the Checklist MFD to interact with it. Then we would have the beginnings of a Mission Control simulation. One step at a time though, of course. I'll get in touch with Jarmo and see if he can help us get Rendezvous stuff into the LTMFD or IMFD.
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meik84
Project Team Member
Sr. Member
Posts: 299
Re: Apollo 7 Rendezvous Procedure
«
Reply #10 on:
June 20, 2011, 03:44:53 PM »
Quote
do we plan on always using the MFDs to calculate maneuvers? Or will the "spacecraft" (as in the Orbiter vessel) be doing that one day?
As long as we want to use the CMC for the maneuvers (which was the case in reality), we will always need MFDs. It'd be a good thing to have one MFD for all tasks, though.
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abr35
Project Team Member
Full Member
Posts: 35
Re: Apollo 7 Rendezvous Procedure
«
Reply #11 on:
June 22, 2011, 05:41:55 PM »
OK I have a rough TPI procedure. You need to know the approximate time of ignition, but P34 is able to search within one orbit if you specify a line of sight angle.
V37E 34E
F06 37 - Time of Ignition
F06 55
R2 LOS Angle - If set to +00000 the LOS Angle will be calculated from TIG, otherwise Noun 37 is used as a starting point to find when the line of sight = Register 2. If you specify Register 2 it alters TIG, if you don't it alters line of sight.
R3 Angle from TPI to Intercept (.01 deg) - This is the angle between the burn and the intercept. It must be entered or the AGC thinks you want to intercept the target at ignition and bad things happen. A +12000 will intercept in a third of an orbit, and seems to work fine. I'm going to try to find the real value
PRO
F16 45
PRO
Wait
F06 55 - R2 Iterated
PRO
Wait
F06 58 PRO
HP after maneuver
dV TPI
dV TPF
F06 81 PRO
dVx
dVy
dVz
F06 69 PRO
not sure what any of these are
F16 45 PRO
marks
Time until maneuver
MGA angle
F37
30E
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eddievhfan1984
Full Member
Posts: 231
Re: Apollo 7 Rendezvous Procedure
«
Reply #12 on:
June 22, 2011, 07:20:47 PM »
Yeah, the GNC checklist says that Noun 69 involves entry data (R1 is BETA, commanded roll position, R2 is G-force, and R3 is SC velocity, if I read it correctly).
And with the EOCA, I know I have it configured properly, but I've done an hour's worth of iterative calculations, and still no solid burn data.
«
Last Edit: June 23, 2011, 11:01:49 PM by eddievhfan1984
»
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jarmonik
Full Member
Posts: 130
Re: Apollo 7 Rendezvous Procedure
«
Reply #13 on:
June 25, 2011, 05:30:05 AM »
There is a pretty good description of rendezvous retrieval targeting maneuvers (CSI, CDH, TPI, TPM) in this document (
http://www.ibiblio.org/apollo/Documents/HSI-208454.pdf
) in a page 225 but but I have no idea what's CCM ? Is that an apollo 7 specific maneuver of some kind ? Obviously, if you want to rendezvous the S-IVB then you have to move away from it at first by executing a few burns.
The calculations doesn't sound very hard but what need to be calculated exactly ? and what are the user input parameters ?
Based on the document the user input parameters for SCI are t1, t3, E and N. But it's very likely that t1 and t3 are computed in ground and therefore aren't exactly an input parameters in the Orbiter.
I made a clean installation of the letest NASSP from the CVS and there seems to be no scenarios except the launch scenario. Therefore, I would appreciate if someone could attach a scenario when the CSM is in orbit undocked form S-IVB and ready for maneuvers.
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meik84
Project Team Member
Sr. Member
Posts: 299
Re: Apollo 7 Rendezvous Procedure
«
Reply #14 on:
June 25, 2011, 07:47:57 AM »
Quote
F06 69 PRO
not sure what any of these are
That's the components of dV in the specified line of sight at TIG, in contrast to N81, which shows the components of dV referenced to LVLH at TIG.
That N55 is one of the problems I'm still facing: we need either TIG or the LOS angle. Which one was used in reality (and, more important, how were they calculated?)? Which value was used for CENTANG?
Edit: Had look at the flight plans: CENTANG was always +13000, elevation angle was +02745 for Apollo 7 and +02660 for Apollo 11. I strongly believe that the elevation angle had the sole purpose to specify the pitch angle the CSM pointed to at TIG, so that the optics pointed at the SIVB (resp. the LM) and the burn could still be executed. This saves time, fuel and reduces the workload for the lonely CMP.
Quote
And with the EOCA, I know I have it configured properly, but I've done an hour's worth of iterative calculations, and still no solid burn data.
Welcome to the club. I've tried several times and still get those 5nm difference between EOCA and orbiter.
«
Last Edit: June 25, 2011, 08:58:10 AM by meik84
»
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