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Why is trash from the ISS sent down in some of the cargo vehicles. Would it not make more sense to dump it overboard in the downward + retrograde direction (as described here) and use reusable cargo craft even if the down mass is less than the trash volume?

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    $\begingroup$ opening a hatch to jetision each piece of rubbish is wasteful $\endgroup$ – JCRM Mar 28 '18 at 21:45
  • $\begingroup$ @Jcrm there is a small airlock on the JAXA Kibo module that might be good for this. $\endgroup$ – geoffc Mar 28 '18 at 22:26
  • $\begingroup$ Every airlock cycle wastes a finite amount of gas. $\endgroup$ – Organic Marble Mar 29 '18 at 4:03
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    $\begingroup$ further, every item of rubbish placed into a departing pressurised vessel reduces the volume of gas lost to that vessel when cargo was removed $\endgroup$ – JCRM Mar 29 '18 at 8:31
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    $\begingroup$ If you had a long linear accelerator, de-accelerating the garbage would push the ISS back to a higher orbit. The specific impulse of garbage is pretty bad, but hey, it's free reaction mass. $\endgroup$ – MSalters Mar 30 '18 at 8:38
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Dumping it into orbit, even retrograde, will still leave objects in orbit, slowly falling down until they burn up. But for that entire period of time, they become possible hazards to anything in that orbit or lower.

A launcher with some minor amount of velocity would speed up the deorbiting, but it would still be there. You would probably want it somehow integrated into an airlock of the appropriate size. Using Quest (US Segment) or one of the Russia segment airlocks would probably waste too much atmosphere with each cycle to be worth it. The JAXA Kibo module has a small experiment airlock that might be better suited, but probably would want something more designed to task.

The Progress/ATV/Cygnus vehicles are there, they are empty, safer to put the trash in there, than anything else.

Ironically, I always thought that filling a Dragon up with any extra volume/mass of garbage would be an interesting business model. Sell the stuff to nutty fans like me. Would you buy space garbage? I probably would, at least once, and there are millions of nutso's like me, all around the world.

Conversely when they swapped out the Hubble solar arrays, they just 'threw' the olds ones away. They are large, so easily trackable. Visually reflective, so trackable. Being large in surface area and light (Aka: Fluffy, and NOT Gabriel Iglesias, even small atmospheric affects become magnified quickly.

Re-reading your question I see implied a secondary question, which is, why are Progress/ATV/Cygnus not recovered, like Dragon/Soyuz are?

That is because re-entry is hard and tricky. In theory Progress should be a piece of cake to make re-entry, since it is basically a modified Soyuz. Just put back the landing features on Progress. (Yes it is not that simple, but you know what I mean. Would cost upmass and so on).

But Cygnus/ATV were never designed to re-enter and land without burning up.

If you are not carrying super valuable stuff (Humans, as Soyuz does) or plan on being reused (Like Dragon has been) then it is not worth the cost/lost upmass that recovery would require.

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  • $\begingroup$ @OrganicMarble True dat. You could have just edited in that fix you know. $\endgroup$ – geoffc Mar 28 '18 at 18:19
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    $\begingroup$ I don't like to edit stuff that changes the meaning in other people's answers. $\endgroup$ – Organic Marble Mar 28 '18 at 18:23
  • $\begingroup$ The comment in the question hits on this, but there's also the issue of getting the trash that's inside the station outside. $\endgroup$ – Tristan Mar 28 '18 at 22:22
  • $\begingroup$ Yeah, who wouldn't pay a fortune for a rag soaked with authentic astronaut sweat... $\endgroup$ – Philipp Mar 29 '18 at 11:38
  • $\begingroup$ @Philipp Admit it, a bag of astronaut poop that was in orbit? Would you really turn it down? I think NASA is very short sighted in this regard. I will be writing to CASIS and see if I can monetize this idea now. $\endgroup$ – geoffc Mar 29 '18 at 11:50

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