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If a large parachute were attached to the ISS, how long would it last? I know that there is very little atmosphere where the ISS orbits, but also that the atmosphere is thick enough that it needs a few boosts every now and then. Would the ISS survive a few orbits with a parachute? How often would it need to perform reboosts to remain stable? Would the parachutes even expand in the thin atmosphere and would they significantly increase drag? If not, how low would the ISS have to be for the parachutes to have a noticeable effect? If the parachutes would be noticeable at the current altitude, how high would it have to be for the parachutes to go largely unnoticed? In general, are drag characteristics considered at all when looking at low earth orbit vehicles?

The size of the parachute should be big enough that if the ISS were to descend into the thicker parts of the atmosphere (ground level), its terminal velocity should be around 20 m/s (pretty fast, but not terribly fast). The ISS masses approximately 370,000 kg right now. Plugging this in to the drag equation, (and using 1.5 as the drag coefficient for the parachute, I made that number up, I don't know if that is the actual drag coefficients for parachutes), we get that the diameter of the parachutes about 112 meters (which is pretty big so I might have done the math wrong).

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    $\begingroup$ Define "large", please. It depends on the diameter. $\endgroup$ – Rikki-Tikki-Tavi Sep 22 '15 at 0:04
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    $\begingroup$ @Rikki-Tikki-Tavi is completely correct. A small "chute" will be in the shadow of the station, a larger one will increase drag beyond what the station has now. Depending on the material, the chute may thin out and degrade because of UV and monoatomic oxygen, though. $\endgroup$ – Deer Hunter Sep 22 '15 at 1:20
  • $\begingroup$ @Rikki-Tikki-Tavi How about this: the parachute should be large enough that if the ISS were to descend on this parachute, its terminal velocity at ground level should be around 20 m/s. I don't know how big that would make the parachute, but it should be pretty big. $\endgroup$ – soktinpk Sep 22 '15 at 23:34
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I'm only going to tackle your final question:

In general, are drag characteristics considered at all when looking at low earth orbit vehicles?

Yes, drag characteristics are considered for LEO vehicles that need to stay up for a long time (like the ISS) or are flying particularly low, like the Gravity Field and Steady-State Ocean Circulation Explorer.

The ISS rotates its solar panels into a minimum drag position while passing on the night side of Earth.

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