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Zelenka
10-16-2008, 08:43 PM
Hi all,
Can anyone help me out here - I need to know the average time it would take the space shuttle to get to the International Space Station, and what sort of factors might affect that time.

It's for a YA SF story for NaNoWriMo and I've got the same sort of setup but on an alien planet / space station. I want to keep things as correct as possible given that the technology is fairly similar though. I've been through a load of pages on NASA's site and some other sites that were (I have to admit) a bit too technical for my poor brain, but so far I've not been able to find this info.

Any help would be greatly appreciated.
Jess

Sarpedon
10-16-2008, 08:49 PM
Well, Russia just sent a Soyuz pod to the ISS.

http://news.bbc.co.uk/2/hi/science/nature/7665782.stm

Here's a link to the launch video. Near the end, the commentator says that the link up to the station will occur 'two days from now.'

A subsequent news story says the capsule arrived 'slightly ahead of schedule.'

I doubt the shuttle will be either faster or slower. I think the amount of time is more dependant on the problem of synchrenizing orbits. Some trips may be faster, some slower.

Zelenka
10-16-2008, 09:31 PM
Fantastic, thank you! I'll check out the link. Since it's not Earth I don't have to be 100% spot-on-accurate, but I still like to keep things within the bounds of possibility. At least now I know what sort of time-frame I'm looking at for that section of the story.

Vincent
10-16-2008, 09:39 PM
Remember that the shuttle will reach orbit very quickly. A matter of minutes. Then both the shuttle and the space station will be in their own unique orbits- they're both circling the Earth every, what, 90 minutes? The rest of the time till docking would be spent reaching the right altitude and drawing those orbits closer.

MelancholyMan
10-16-2008, 10:38 PM
What you are talking about is called an "Orbital Rendezvous" maneuver and is pretty complicated. It is usually done through a series of what are called, "Hohmann Transfers," alternately elipticizing and circularizing the orbits. Warning: It is highly non-intuitive.

For instance, if the ISS is ahead of you, you would actually slow down in the direction of your motion to reach it. What this does is lowers the perigee on the other side of the orbit causing you to orbit faster. Then, once you've caught up, you would wait until you are at perigee, then apply a delta-V (change in velocity) in your direction of motion to circularize your orbit. Everything in space is done by calculating the magnitude and direction of your delta-v, then applying it at the right time.

The mission is planned out well in advance and the shuttle would fly an ascent trajectory specifically designed to put it in the right place to rendezvous with the ISS after the maneuvers. It is very important that the shuttle reach orbital insertion within a few kilometers(or less) of where it needs to be. There will never be any guess work since the missions are completely and totally modeled using what are called Six Degree of Freedom Simulations, or 6-DOFs. That's actually what I do for a living.

Knowing where these two objects are is of primary importance. During ascent the position of the shuttle will be maintained by onboard instruments consisting of an inertial measuring unit that sense acceleration and rotation and software that takes these measurements and calculates your position using it's own internal 6-DOF. Once in orbit it will maintain this navigation solution and will also receive updates from ground-based radars. The ISS also has an IMU and radar navigation solutions. Ground based measurements can determine the position of satellites to within a few feet.

The entire process is usually designed to take a day or two and is entirely dependent on the orbital insertion position of the shuttle with respect to the ISS. As they get close they are very careful, with closing velocities between the shuttle and the station on the order of just a few meters per second, coming down to inches per second on final approach. Collisions in space are very, very bad, just ask the Russians.

If you have any more questions feel free to PM me.