Author Topic: Why does it take so long to get to ISS?  (Read 21602 times)

Offline Jorge

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Re: Why does it take so long to get to ISS?
« Reply #20 on: 05/12/2009 07:48 pm »
Does anyone know how fast orion could reach ISS?

It is rarely a matter of "could"; Soyuz could do FD1 rendezvous with ISS but the Russians chose FD3, for the same launch window availability/timeline standardization reasons that drove the shuttle there.

Both FD1 and FD3 profiles have been developed for Orion. FD3 is baselined right now but that could change. As with the shuttle, it's a trade off between time-to-rendezvous and launch window availability. Unlike the shuttle, Orion should not require nearly so much on-orbit reconfig. But Orion could very well wind up keeping FD3, just like Soyuz.
« Last Edit: 05/12/2009 07:50 pm by Jorge »
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Offline Spacenick

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Re: Why does it take so long to get to ISS?
« Reply #21 on: 05/12/2009 09:37 pm »
I understand, it would also be interesting how much plane change an Orion can do once in orbit, for example would it be possible to fly a Orion docked to the ISS to a potential Chinese space station or a Bigelow one? Do you think the Mir -> Salyut 7 -> Mir flight will be the last time a manned spacecraft goes from one space station to another, for the next 25 years?

Offline Jorge

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Re: Why does it take so long to get to ISS?
« Reply #22 on: 05/12/2009 09:40 pm »
I understand, it would also be interesting how much plane change an Orion can do once in orbit, for example would it be possible to fly a Orion docked to the ISS to a potential Chinese space station or a Bigelow one? Do you think the Mir -> Salyut 7 -> Mir flight will be the last time a manned spacecraft goes from one space station to another, for the next 25 years?

Mir was deliberately launched in-plane with Salyut 7 so Soyuz T-15 didn't need to do any large plane-change burns.

I expect Orion, like the Apollo CSM on the Skylab missions, will need a propellant offload that will restrict its plane-change capability to within a few degrees of ISS.

I don't rule out a station-to-station flight but it *requires* that the new station be launched - and maintained - in-plane with the old one, as was done with Mir/Salyut 7.
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Online mmeijeri

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Re: Why does it take so long to get to ISS?
« Reply #23 on: 05/12/2009 09:45 pm »
I expect Orion, like the Apollo CSM on the Skylab missions, will need a propellant offload that will restrict its plane-change capability to within a few degrees of ISS.

Why would the propellant offload be needed?
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Offline Spacenick

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Re: Why does it take so long to get to ISS?
« Reply #24 on: 05/12/2009 09:52 pm »
I guess for Bieglow it would make sense to launch any station in an orbit compatible with the other stations available, I'd guess it is a potential safety increase and it might also be dictated by the north atlantic anomaly and by the fact that Bigelow probably wants it's station to be reachable by Soyuz spacecraft (unless  the Russians launch manned Soyuz from koruou in the future that would mean at least 51 degrees)
Will be very interesting to see what Orbit the Chinese will choose for their stations.
If they want to run it for a longer period of time like Mir was they might also want to make it possible to let Russian spacecraft visit, especially since there would be much less political problems then between China and the US
« Last Edit: 05/12/2009 09:56 pm by Spacenick »

Offline Jorge

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Re: Why does it take so long to get to ISS?
« Reply #25 on: 05/12/2009 09:54 pm »
I expect Orion, like the Apollo CSM on the Skylab missions, will need a propellant offload that will restrict its plane-change capability to within a few degrees of ISS.

Why would the propellant offload be needed?

Launch vehicle (depends on which launch vehicle we end up with, of course).
JRF

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Re: Why does it take so long to get to ISS?
« Reply #26 on: 05/12/2009 09:54 pm »
Ah, I see, I had mentally discarded Ares I already. :)
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Offline Jim

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Re: Why does it take so long to get to ISS?
« Reply #27 on: 05/13/2009 12:09 am »
I guess for Bieglow it would make sense to launch any station in an orbit compatible with the other stations available, I'd guess it is a potential safety increase and it might also be dictated by the north atlantic anomaly and by the fact that Bigelow probably wants it's station to be reachable by Soyuz spacecraft (unless  the Russians launch manned Soyuz from koruou in the future that would mean at least 51 degrees)


No he has other requirements.   He is looking at lower inclinations (40 degrees I think I read).  He would like more launch opportunities per day
« Last Edit: 05/13/2009 12:10 am by Jim »

Online mmeijeri

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Re: Why does it take so long to get to ISS?
« Reply #28 on: 05/13/2009 12:16 am »
No he has other requirements.   He is looking at lower inclinations (40 degrees I think I read).  He would like more launch opportunities per day

I thought you always had precisely two opportunities per day, each time you pass through the line of nodes. What am I confusing this with?
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Offline Nomadd

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Re: Why does it take so long to get to ISS?
« Reply #29 on: 05/13/2009 01:46 am »
No he has other requirements.   He is looking at lower inclinations (40 degrees I think I read).  He would like more launch opportunities per day

I thought you always had precisely two opportunities per day, each time you pass through the line of nodes. What am I confusing this with?

 Think of the extremes. A Polar orbit would only give you two chances a day. Maybe less if you can't afford to hit an orbit at least 12 degrees off your launch site. An equatorial orbit, and you could pretty much launch any time. The lower the inclination, the more often it will be within your limits.
« Last Edit: 05/13/2009 01:48 am by Nomadd »
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Offline vt_hokie

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Re: Why does it take so long to get to ISS?
« Reply #30 on: 05/13/2009 03:59 am »
Do you think the Mir -> Salyut 7 -> Mir flight will be the last time a manned spacecraft goes from one space station to another, for the next 25 years?

Wow, I never knew that happened!  Interesting!

Offline Jorge

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Re: Why does it take so long to get to ISS?
« Reply #31 on: 05/13/2009 04:11 am »
Do you think the Mir -> Salyut 7 -> Mir flight will be the last time a manned spacecraft goes from one space station to another, for the next 25 years?

Wow, I never knew that happened!  Interesting!

Here's a good article by Sven Grahn detailing the intricate orbital maneuvering required to make the whole thing happen:

http://www.svengrahn.pp.se/histind/MirtoSal7flyover/MirToSal7Flyover.html

Note that the delta-RAAN between the two stations was maintained within 0.1 degrees for the Soyuz transfers. Also note the many discontinuities in the plot of Mir orbital period - each one of those represents a maneuver by Mir.

Bottom line is that this is a tricky thing to do even when both stations are initially launched into the same plane.
JRF

Offline yinzer

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Re: Why does it take so long to get to ISS?
« Reply #32 on: 05/13/2009 05:06 am »
No he has other requirements.   He is looking at lower inclinations (40 degrees I think I read).  He would like more launch opportunities per day

I thought you always had precisely two opportunities per day, each time you pass through the line of nodes. What am I confusing this with?

In practice, you have a launch window, not a launch instant.  You can launch whenever your launch site is within 50 miles (or something) of the orbital plane.  Your launch site moves due east.  If you are launching into a high inclination orbit, your launch site goes through the orbital plane at a sharp angle, quickly.  If you are launching into a lower inclination orbit, the launch site goes through the orbital plane at a gradual angle, taking more time, giving you longer launch windows.

If you are launching into an orbit with an inclination slightly higher than your launch site, you end up with one very long launch window (which can be thought of as many smaller windows).

Compare the lengths of the horizontal red lines in the attached pictures - the high inclination orbit is ISS, the low-inclination orbit is STS-125.

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Online mmeijeri

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Re: Why does it take so long to get to ISS?
« Reply #33 on: 05/13/2009 12:11 pm »
Thanks!
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