General Question Simulation to Real Life NASA Comparison II

[PaulG]

Ok, thank you all who answered and posted in http://orbiter-forum.com/showthread.php?t=5744 it was quite helpful.

I can now get into orbit perfectly, onto the "onramp to the ISS". In fact, because of all the posts, its the 2nd easiest thing for me to do! Landing the shuttle is also a snap now.

But my next question is this, HOW does NASA get the shuttle to meet up with the ISS? Let me just say, I know how to approach and dock, I do it quite easily with DG. My question, is simply how does NASA do it with the shuttle?

I have seen the tutorial, but here is the problem, the one I have seen happens to have both the node AND the ISS over the shuttle position. Most of the time this isn't the case. In the most recent shuttle mission, the shuttle launched far away from the position of the ISS.

So, I get into orbit with a MECO at approximately 40km PeA and 240km ApA. Is this the altitude that the real shuttle reaches?

So, then, prograde level to bring PeA up. But, I'm ahead of the ISS so I need to slow down. I know how to do that, increase the orbital diameter...and wait.

So, what does the real shuttle bring its orbit to?

Thanks,
Paul

 

[Tommy]

I think the shuttle stays in the lower orbit and catches up to the ISS. It can take a few days, but the shuttle doesn't have enough delta-v to go to a higher orbit to let the ISS catch up. I seem to recall that some shuttle missions have had rendevous five days or more after launch for this reason.

 

[Arrowstar]

From what I understand, the orbiter periodically performs a burn to slowly raise the orbit of the orbiter to match that of the ISS and thus A) arrive at the ISS, and B) arrive at the ISS slowly enough where you can stop.

 

[tblaxland]

So, I get into orbit with a MECO at approximately 40km PeA and 240km ApA. Is this the altitude that the real shuttle reaches?

Pretty close to it.

So, then, prograde level to bring PeA up. But, I'm ahead of the ISS so I need to slow down. I know how to do that, increase the orbital diameter...and wait.

So, what does the real shuttle bring its orbit to?

Roughly circular to begin with and then it is slowly raised over the course of a couple of days so that it gradually matches the station's orbit. But it always stays below the stations orbit and it just waits until it catches up the station from behind.

 

[PaulG]

Thanks. So it brings the orbit to about 240k PeA 240 ApA?

I tried this out last night and it worked well. Basically, I held this orbit until I was starting to get close to the ISS. Then, I raised ApA to the ISS altitude. About 3-4 orbits out, I started to increase PeA to slow down my speed (match ISS). At that point, a rendezvous was pretty simple with low dV and decent distance.

I guess I was thrown off by the fact it took over 200k seconds....which is about 2 days anyway.


Thanks!

 

[Urwumpe]

Well, you should also learn the sense behind the NASA maneuvers The Shuttle does more maneuvers than minimal needed, for making the calculations of following maneuvers simpler and reducing the effect of inevitable measurement errors.

http://www.shuttlepresskit.com/STS-88/REF54.htm

 

[ar81]

Imagine that ISS orbit is passing on top of you.
You throw a stone called "space shuttle" so it reaches ISS.
You have almost no plane alignment because it is very fuel expensive.
Shuttle travel below station orbit to reach it, using third law of Kepler, AFAIK.

 

[PaulG]

Yes, I know. Question was, how does the shuttle do it in real life. Got the answers above, thanks.

 

[Bj]

Imagine that ISS orbit is passing on top of you.
You throw a stone called "space shuttle" so it reaches ISS.

Except the space shuttle is more like a flying brick than a stone...

 

[ar81]

Except the space shuttle is more like a flying brick than a stone...

It is a stone with the shape of a flying brick and some exotic materials.:lol:

 

[PaulG]

Thanks, this is quite helpful. I was on nasa's site reading the chronology of the last flight and saw many of these terms, but didn't know what they meant.

Thanks again for the comments!
Paul

Well, you should also learn the sense behind the NASA maneuvers The Shuttle does more maneuvers than minimal needed, for making the calculations of following maneuvers simpler and reducing the effect of inevitable measurement errors.

http://www.shuttlepresskit.com/STS-88/REF54.htm