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Old 03-13-2019, 07:29 PM   #181
indy91
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 One other question that's been bugging me since I've been looking more closely at the rendezvous portion of shuttle flight plans...see picture.
Let's assume a target is in a 400km circular orbit, while a chaser vehicle is in an elliptical 380x400 orbit (so mean altitude being 390km). The velocities in each case will be:

Target: 7672.6 m/s
Chaser at perigee: 7689.6 m/s
Chaser at apogee: 7666.9 m/s

So the average speed of the chaser is definitely faster than the target and it will catch up in the lower orbit. But at apogee the chaser is going slower than the target, which means it will not catch up, but instead fall back a bit. That's how you get that kind of loop. This effect will be more pronounced if the chaser is in a more elliptical orbit.
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Old 03-13-2019, 08:59 PM   #182
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Originally Posted by Tim13 View Post
 One other question that's been bugging me since I've been looking more closely at the rendezvous portion of shuttle flight plans...see picture.
I think it is due to the distance between the target and the chaser which is not always constantly decreasing. The graph shows that as the chaser passes Apoapsis after the burn the distance on the X axis starts increasing and then it decreades again as it proceeds towards periapsis
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Old 03-13-2019, 11:19 PM   #183
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  But at apogee the chaser is going slower than the target, which means it will not catch up, but instead fall back a bit. That's how you get that kind of loop. This effect will be more pronounced if the chaser is in a more elliptical orbit.
I guess what was tripping me up, was in my mind, if both the target and the chaser's maximum orbit height is 400km, then when the chaser is at 400km during apogee, it would be at the same speed as the target, not slower. So it's the elliptical shape of the chaser orbit that is the key as to why the RDVZ depiction has the "loop."

I do understand what you mean, and your example is a good demonstration of it. I just need to give it a think, to wrap my brain around it.

I hope my questions are not a distraction. I enjoy learning about these things. It keeps the grey matter sharp.

Thanks,

Tim

Last edited by Tim13; 03-13-2019 at 11:27 PM.
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Old 03-14-2019, 12:01 AM   #184
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 I guess what was tripping me up, was in my mind, if both the target and the chaser's maximum orbit height is 400km, then when the chaser is at 400km during apogee, it would be at the same speed as the target, not slower. So it's the elliptical shape of the chaser orbit that is the key as to why the RDVZ depiction has the "loop."

Remember hat the speed depends on radius and semimajor axis. If you are catching up, you are in an orbit with a lower semimajor axis (= shorter orbit period) . Since conservation of energy applies in Orbit that means, since you have less energy available in an Orbit with a lower semimajor axis, that at the same altitude ( = potential energy), you will have less kinetic energy (=speed).
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Old 03-14-2019, 12:17 PM   #185
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...and there's the eureka moment of enlightenment. That makes perfect sense.

Thanks,

Tim
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Old 03-14-2019, 07:14 PM   #186
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Hi y'all - I stumbled across this during a web search for something else.

"Shuttle FDO" obviously caught my eye, as I was a Flight Dynamics Officer in the Space Shuttle MCC from 1986-1997. And, as I read through this, a lot of great details were being discussed - including some pretty savvy/correct comments on maneuver planning. I wrote (or helped write) sections of the FCHB (and some of the FDO workstation trajectory processing software), so glad you enjoyed it.

I'll go back and look through this some more - but in the meantime, if there's anything I can help with, please let me know.

For more info, you can browse through my space sites:

-THE TRENCH-

MCC Overview

What's a FDO?
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Old 03-15-2019, 07:40 PM   #187
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...also, I've been talking with Indy, and he's got a pretty sharp head on his shoulders about this - rather esoteric - topic! Computing (and fully understanding!) rendezvous maneuvers, especially ground-up, is definitely PhD-level orbital mechanics.
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Old 03-15-2019, 08:14 PM   #188
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Welcome to the forum!
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Old 03-15-2019, 08:16 PM   #189
indy91
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Thank you for your kind words. I almost named it "OMP MFD", and for about 5 minutes I actually did, but that acronym clashed with something else Orbiter related, the Orbiter Multiplayer project. The Orbital Maneuver Processor is still most of what this project tries to do, so it would still be a fitting name as well.

Welcome to the forum, Roger! I am sure the SSU guys and me will be able to come up with a question or two to ask you.

And speaking of the OMP, here the next release version: https://github.com/indy91/Shuttle-FD...ag/0.1.8-alpha

The only change in this is:

-Improved accuracy and iteration behavior of NPC maneuvers with non-spherical gravity

With this and non-spherical gravity enabled I tested a STS-82 rendezvous and the NPC maneuver was very accurate. NCC and TI both had only 0.3 ft/s of out-of-plane DV to correct for a remaining plane error.
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Old 03-15-2019, 09:29 PM   #190
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Well, I am more interested in the "boring" questions right now: How is the work of a FDO like beyond the console? (Or how NASAs homepage puts it: "the other 75% of the time"). How is a FDO for example involved in mission preparation?

And of course: In many German workplaces, its common to play more or less evil jokes on the new employees, and from what I can tell, its not unknown in other countries... did anything like that happen to you on our first day at NASA?
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Old 03-15-2019, 09:45 PM   #191
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Originally Posted by Urwumpe View Post
 Well, I am more interested in the "boring" questions right now: How is the work of a FDO like beyond the console? (Or how NASAs homepage puts it: "the other 75% of the time"). How is a FDO for example involved in mission preparation?
Awesome question, and YES ... FDOs were critically involved with mission design and preparation. There was an entire Flight Design organization, which was HUGE, that was responsible for a lot of the pre-flight planning, generic and flight-specific techniques and procedures, post-flight evaluation and updates, etc. The FDO was a key part of that, with the Lead FDO assigned for each flight participating directly with the Flight Design Manager assigned for that flight. Together, they would work with the mission objectives, review if previous missions were similar for reuse, work with the FD teams for trajectory optimization, be the primary interfaces with the crews when new trajectory techniques were to be developed, work with the other Flight Controllers when things overlapped (working with Payloads, PROP, Guidance/GPO, etc.).

Then - there were the simulations. LOTS and LOTS of simulations. We had "generic" (training for both new and experienced teams) sims and "Flight Specific" sims that used the actual assigned crew, performed actual planned flight objectives, etc. The sim types included Ascent sims (including both nominal and abort runs - they'd do numerous ones in a given day, with debriefs after each one), Orbit sims (sometimes "just the one day" and sometimes multi-day "Long Duration" sims to practice planning/handover/execution activities), and Entry sims (which would be either a Deorbit-through-Landing sim or sometimes just the "200K" runs, which would be from 200K feet through landing - so they could do several in a given day).

Remember, too, that FDOs were assigned to multiple flights at any given time - so while I might have been Lead FDO on one or two upcoming flights, I was also assigned to a non-Lead shift for several others... or, as a Senior FDO, would be training new people - so had to both provide sim scenarios *and* sit with the newbies on console for training... or sometimes sit in the generic sims if they wanted a few more experienced team members sprinkled into the mix to show the newbies how to respond to the failures that the Sim team ALWAYS threw at us!

... and, of course, there was the training. Always looking at Flight Rules, new procedures (participating in and defending them in Flight Techniques meetings with crew/Flight Directors asking oh-so-tough-but-necessary questions), documentation updates, and the normal office stuff.

We were *never* without something (really really cool) to do.

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Originally Posted by Urwumpe View Post
 And of course: In many German workplaces, its common to play more or less evil jokes on the new employees, and from what I can tell, its not unknown in other countries... did anything like that happen to you on our first day at NASA?
First Day? Not so much ... but throughout the career? Oh yes indeed!

In the "old MCC" (Apollo era) before we transitioned to the new MCC, the consoles still had pneumatic tube systems for sending hardcopies, notes, etc., to other console stations both in the MCC and in our back-rooms (MPSRs). One of my favorite jokes was to send a p-tube full of "anti holes" (the little paper circles cut out by the three-hole punch so that documents could be put into three-ring binders) to an unsuspecting newbie in the MPSR. They'd hear the p-tube "arrive" with a resounding THUNK, dutifully think "Oh! FDO just sent me something, I'd better go open it right away!"

Which, of course, would result in the newbie being showered with anti-holes.

On a side note, and "not intended as a joke", jelly donuts do *not* travel well in p-tubes.
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Old 03-16-2019, 04:20 AM   #192
Gingin
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Welcome RamJet, nice to have a real life FDO there
Be ready for many questions though

Very nice FDO site.

Quick question, on which STS missions did you work on ?
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Old 03-16-2019, 10:25 AM   #193
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Welcome to the community RamJetFDO! I hope you will not only have the patience to read our questions but also to understand our frustration when we try to do something with FDO MFD and it doesn't really go as expected..

---------- Post added at 11:25 AM ---------- Previous post was at 11:14 AM ----------

BTW since a good starting point in order to work with FDO MFD is to have the original STS mission plans available (details about phasing and rendezvous burns) we have the "Attitude Timeline" in the Flight Plan only for some of the missions (if I remember well STS-114 to STS-118 only). Do you know if the same info are available for the other STS missions (I searched on the web but could not find anything really useful)?
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Old 03-18-2019, 05:48 PM   #194
Tim13
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Only in an orbiter forum, does a real FDO show up, and we all get excited. I love being part of a nerd nation! LOL.

This made my day.

Tim
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Old 03-18-2019, 07:23 PM   #195
RamjetFDO
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Originally Posted by Gingin View Post
 Welcome RamJet, nice to have a real life FDO there
Be ready for many questions though

Very nice FDO site.

Quick question, on which STS missions did you work on ?
Thanks for the kind greetings... and, in some form or the other, I was a part of STS-26 through -86, though my first flight on console was for the GRO deploy on STS-37. My last flight was STS-86 (and I had done all of the Mir missions prior to that).
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