What determines ISS altitude?

[vt_hokie]

I'm curious, what drove the decision to place the ISS in its current altitude range (~220 statute miles, iirc)? Is it simply a tradeoff between atmospheric drag and ability to deliver payload? Placing the station in a 300+ mile high orbit, like that of the Hubble, would certainly reduce drag and hence reduce the number of reboosts needed. On the other hand, NASA already suffered a significant hit by putting the station in a 51.6 degree inclination orbit, and I'm guessing that reaching a higher orbit of that inclination would not be feasible without cutting payload capacity significantly. Would the space station have been placed higher had it been in a 28.5 degree inclination orbit? Also, I forget, how high can a manned station go before radiation exposure becomes unacceptable? I assume it's wherever the inner Van Allen belt starts...

 

[giofx]

because it have to be serviced by the russian who launch from baikonur... in fact Mir was on the same altitude/inclination.

 

[vt_hokie]

I was wondering if, after the station is more or less completed, it might be feasible and/or desirable to boost the station to 250 miles or more in order to reduce drag somewhat.

 

[giofx]

so you will need more propellant for the shuttle, soyuz, progress and the ariane-ATV to get to the station.

 

[vt_hokie]

True, and if they put it in a 150 mile orbit, they would need less propellant to reach it! Everything is a tradeoff...

 

[giofx]

"Good for you, you used the word propellant rather than fuel. Thank you. "<br /><br />its only one of the first things i learned from you or najab... <img src="/images/icons/smile.gif" /><br /><br />and we don't want to speak as the avarage media, don't we? <img src="/images/icons/tongue.gif" />

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>because it have to be serviced by the russian who launch from baikonur... in fact Mir was on the same altitude/inclination.<p><hr /></p></p></blockquote><br /><br />To elaborate a bit, it's because it has to be serviced by Soyuz rockets from Baikonur <i>and</i> Shuttles from Florida. The altitude is actually lower than what the Russians would prefer. It's more efficient to get to ISS from Baikonur (which is at 51 degrees north latitude, and it's not a coincidence that that's the same as the ISS's orbital inclination) so they can afford to fly a bit higher into that inclination. If the ISS is higher, it doesn't need to be reboosted as often. For this reason, while the Shuttle was unavailable for the last two years, they pushed the ISS into a higher orbit, out of the Shuttle's reach. They allowed it to drop back down in time for STS-114, of course.<br /><br />So the orbit is basically the best compromise between Soyuz rockets from Baikonur and Shuttles from KSC.<br /><br />The Russians actually originally intended Mir-2 (the core of which ultimately became Zvezda, during its greatly extended planning phase) to be in an orbit which Shuttles cannot acheive. It would've been a polar orbit, servicable by Soyuz rockets launched from the far north site of Plesetsk. This was intended to resolve the problem of renting space from a foreign country after the breakup of the Soviet Union and the loss of Kazakhstan. But for a variety of reasons this never became a reality. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>