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ISS might be destroyed soon, de-orbiting for a controlled reentry into the Pacific Ocean.

Why isn't simply pushed away from Earth to an outer stable orbit (not sure if it's possible) or even into an interstellar space voyage?

Maybe it has not any scientific value (specific probes are better and specifically designed for this task) but at least they will not destroy that amazing technological achievement and it may still contribute to research during its sunset (specific instruments may even be carried on board).

I don't think it will use more propellant than a controlled re-entry.


Edit: yes, I'm thinking about all those experiments involving bacterial, fungi and degradation of materials. Also viruses, no safety concerns because there won't be any crew. A slowly moving ISS can run (some of) those experiments for the next 10 years sending results back to Earth. Also new experiments for a possible long-time trip to Mars...

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    $\begingroup$ Everything in space is falling into a gravity well, so even if we managed to boost the ISS out of Earth orbit we would still need to achieve the escape velocity of the sun. Escape velocity from the sun, from Earth orbit is ~40km/s, compared to ~11km/s to lift from Earth's surface. $\endgroup$ – RIanGillis Jan 10 '18 at 16:32
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    $\begingroup$ Since "low Earth orbit is halfway to anywhere" in the solar system, we "only" have to repeat that effort and the ISS can go anywhere! (That was sarcastic. Note the "only".) It took 27 Shuttle flights, 2 Proton flights, 2 Soyuz flights, and 1 Falcon 9 flight to bring the various pieces that eventually became the ISS into low Earth orbit. That was a herculean effort. Maintaining the ISS in low Earth orbit is extremely expensive. Making it go beyond low Earth orbit would be beyond extremely expensive. $\endgroup$ – David Hammen Jan 10 '18 at 18:48
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    $\begingroup$ @DavidHammen I wrongly thought that to move it far enough was a somehow cheap task. I see I was completely wrong about that. I'd love to see it in a "museum" but I understand that any effort (budget) is better placed for future missions. 27+2+2+1 flights?!?! If that was the effort required for the ISS I doubt we will ever see a base on the moon!!! $\endgroup$ – Adriano Repetti Jan 10 '18 at 20:05
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    $\begingroup$ @DavidHammen it's fine, we launch more rockets into space, bit by bit upon many other rockets, then we launch many more rockets to carry all the fuel, and we will eventually reach the required amount to save the ISS! Curse you Tsiolkovsky $\endgroup$ – Baldrickk Jan 11 '18 at 9:22
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    $\begingroup$ Well, it could fall out of the sky and hurt someone $\endgroup$ – Machavity Jan 11 '18 at 16:22
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The ISS is not designed to be run unmanned, entirely. The staff on board, when there are 6 astronauts, between exercise, sleeping, and maintenance get a single person-day of science work completed. (That is an 8 hour days' worth).

The ISS is at a fairly low orbit, so that Soyuz, Dragon, CST-100, Cygnus, and the Shuttle can reach it. De-orbiting it will take significantly less fuel than boosting its orbit to something that will not reenter in the long term. Even more so compared to boosting it to escape velocity from Earth. Nor is it designed to sustain the kind of thrust that would be needed to get to escape velocity using existing hardware on station, or existing technologies. (I am ignore VASIMIR and relying on existing technologies.)

Why not keep it manned longer? We have discussed this in many other questions and answers on the site before:

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    $\begingroup$ I wrongly thought that its orbit wasn't that low to require a huge boosting to be pushed out. If that's required then structural integrity, fuel and engines become an halting problem. What a pity! $\endgroup$ – Adriano Repetti Jan 10 '18 at 14:33
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    $\begingroup$ @peterh VASIMR requires enormous amounts of electrical power, far more than the ISS can provide. (I am not talking about the proposals to test VASIMR at the ISS, although I think those have been abandoned) And the ISS's only purpose is to house humans. There is no reason to continue to operate it unmanned. $\endgroup$ – Organic Marble Jan 10 '18 at 15:40
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    $\begingroup$ @OrganicMarble It was not, the NASA stepped back after Ad Astra had a full working prototype ready to launch. The Ad Astra still works for the NASA, although I doubt what useful can they do. Most probably they are waiting for some new project (maybe for a Mars probe). Currently there are no plans to use VASIMR anywhere. My impression is that something in the NASA/USA top management simply doesn't want a breakthrough in the space exploration and so is it. $\endgroup$ – peterh Jan 10 '18 at 16:49
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    $\begingroup$ "Nor is it designed to sustain the kind of thrust that would be needed to get to escape velocity." I don't see how this is true. It's already in orbit so you can push on it however slowly you want to grow its orbit and then push on it however slowly you want to increase its eccentricity. $\endgroup$ – UTF-8 Jan 10 '18 at 22:28
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    $\begingroup$ "Nor is it designed to sustain the kind of thrust that would be needed to get to escape velocity." The amount of thrust needed is inversely proportional to the time. If it we moved over several years, the thrust would be very small. $\endgroup$ – Acccumulation Jan 11 '18 at 21:35
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Let's explore the options:

  • Try to keep it flying: due to structural and other stress, you would need to replace parts of the ISS. You might end up with a situation like Mir where more time is spent patching the station than actually making use of it and waste a lot of money and time.
  • Just abandon the ISS: Not a good idea, its orbit decays and the ISS would thus fall back to earth uncontrolled. Parts may hit inhabited areas. Maybe even large areas.
  • Increase its orbit a bit so it won't hit earth in the next few years: just a temporary solution that only wastes money and creates headaches.
  • Push the ISS far out (leave earth orbit): a very expensive option, it would require a lot of fuel to push that much mass into interstellar space. AFAIK no currently available solution would be available. The on-board tanks can only hold enough fuel for a measly ∆v of 50m/s, but a ∆v of about 3220m/s is required to reach earth escape velocity from LEO. You would need to develop and build a solution for that and fly a lot of missions.
  • Make the ISS take a controlled dive into the atmosphere where it burns up: Since it's very costly to keep it up, it must come down. With this option, you get to control where and when it comes down and "only" requires to develop and build a modified Progress.
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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – PearsonArtPhoto Jan 11 '18 at 12:24
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    $\begingroup$ Another option is to just nuke it from orbit. (!) $\endgroup$ – Mehrdad Jan 15 '18 at 7:57
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    $\begingroup$ @Mehrdad It's the only way to be sure... $\endgroup$ – Oscar Bravo Jan 15 '18 at 9:37
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    $\begingroup$ @Mehrdad it would crack in half and the Earth could pass between the two pieces, safely preventing Armageddon! Wait... what? $\endgroup$ – Magic Octopus Urn Jun 15 '18 at 12:03
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    $\begingroup$ @Mehrdad space.stackexchange.com/q/31363/4703 $\endgroup$ – Lightness Races in Orbit Oct 17 '18 at 9:32
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The problem with the ISS is that it cannot simply be left in its current orbit, because there is a (miniscule) amount of atmospheric drag acting on the structure to continually slow it down. Since the first module was placed in orbit, we've had to periodically boost the ISS back up to its nominal orbit (e.g. using the space shuttle's RCS engines while it was docked, or the station's main engines on the Zvezda module) to compensate for the effects of drag. There are additional forces which perturb the orbit (irregular density of the Earth, solar wind, variations in atmospheric density and composition, etc.) but drag is by far the biggest factor.

If left alone, this drag force will eventually slow the ISS so much that it falls from orbit on its own, and we won't be able to control when and where that occurs. Something that massive falling from orbit poses a safety hazard, so by intentionally de-orbiting the station at a time and place of our choosing, we can control where it falls so that nobody is put at risk.

Now the considerations for saving the station:

  • We would have to configure the station such that it can remain intact and safe if left unmanned and unmaintained for a long time
  • We would have to move the station into a stable orbit that is out of the way of any other operational vehicles

The first point is actually more difficult than it first appears. The ISS is very heavily dependent upon its crew for repairs, and wouldn't be able to function for more than a few months without maintenance, so most, if not all systems would have to be shut down. You might be able to run some low-power, self-contained experiments on board, but that runs into the next problem:

The station is huge, but actually very delicate. Things like radio antennas and solar arrays would have to be stowed or removed, otherwise they could exacerbate the effects of getting hit by small debris. The solar arrays in particular can also contribute to undesirable rotation of the station (due to gravitational gradient and solar wind effects) which could ultimately damage the station. Without solar arrays, there is no power, and without power, there is no attitude control, monitoring or communications, and most importantly, no thermal control. The station would have to rely entirely on passive heating and cooling, which aren't the most stable things in orbit.

Finally, the station contains a lot of volatile materials such as coolant liquids, water, air, thruster gases, etc. Most of these would have to be vented from the station beforehand, because any leakage later on could act like a small thruster, causing the station to rotate or change orbit in an undesired way. Batteries and fuel cells would have to be removed or fully discharged to avoid undesirable (and potentially explosive) chemical reactions in the uncontrolled environment aboard the station.

Now to the second point: getting the thing out of the way. You actually don't have to go to interstellar space to preserve the station, as some other answerers have suggested; the Moon has been in stable orbit for millions of years and will happily remain so for millions to come. The question is: how far do you have to go to avoid bothering other satellites and rockets? The answer is a graveyard orbit, an orbit a few hundred to a few thousand kilometers above geostationary where old satellites go to die. Objects placed in such an orbit can theoretically stay there forever.

This is the bugaboo: because the ISS weighs a staggering 420 metric tons, it would require an enormous amount of propellant to move that bulk from 400km to 37,000km! (Think Saturn-V levels of propellant.) Nobody wants to pay for the rocket(s) and fuel to do that, or all of the preparatory work for Bullet 1 above.

So while I and many others would agree that we should preserve the ISS as a matter of World Heritage, unfortunately the cost to do so would be, quite literally, astronomical.

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    $\begingroup$ "using the space shuttle's main engines while it was docked" Um, no. The main engines were only used for ascent, and in fact had no fuel in orbit. Only the shuttle's tiniest RCS jets were used to reboost the station. $\endgroup$ – Organic Marble Jan 10 '18 at 20:32
  • $\begingroup$ Also, delta-v is not a function of mass. $\endgroup$ – Organic Marble Jan 10 '18 at 20:38
  • $\begingroup$ Ah, good catch sir! Was typing in a hurry and mixed up my jargon. And good call on the shuttle engines; had to go look that up. Learn something new every day! $\endgroup$ – MikeB Jan 10 '18 at 23:13
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    $\begingroup$ @MikeB, you don't need to go all the way out to the geosynchronous graveyard orbit for long-term storage. An orbit up above the useful Sun-synchronous orbits but below semi-synchronous orbit isn't going to conflict with much, while only requiring a huge amount of propellant. $\endgroup$ – Mark Jan 10 '18 at 23:38
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    $\begingroup$ @Mark, the reason orbits between sun-sync and GEO are mostly empty is because the inner Van Allen radiation belt is there, beginning around 1,000km and extending out to 6,000km. Though this wouldn't be a huge problem if the station is defunct, it is nonetheless a harsh environment that would degrade the station over time. I suppose you could send it between 6,000km and GEO without too much fuss, not a bad idea. $\endgroup$ – MikeB Jan 11 '18 at 0:42
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It doesn't, not really, but there will come a time when it will simply not be worth keeping it up. Eventually the solar panels will not produce enough power, some airtight joint will break, or something similar. Right now the station is planned to be used until 2024. There is a study going on to see if it can last until 2028. The things that they are the most worried about are:

  • Thermal cycling abuse- It seems likely this won't be an issue from studies so far.
  • Solar panels- By the year 2028, the solar panels will have degraded about 30%. This might be an issue, and is the most likely item to cause problems.
  • Electronics are out of date- Might need some fairly major updates. But this could be avoided if required.
  • Cost- The ISS costs NASA bout $3.5 billion to maintain per year. That money could go elsewhere that might be more productive.

The bottom line is, I expect that the ISS will continue to be in use for as long as it makes sense to keep it operating. It cost a large amount of money to get it up there, and I expect until the station could be replaced, it will remain up there.

Of course, this could all be moot. If SpaceX managed to get the BFR working, it will essentially be the size of the space station. That would reduce the operating cost of the ISS somewhat, but it would also make it redundant. There are other companies talking about building their own space stations as well. Mars will likely be a major target then.

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  • $\begingroup$ Then the point is simply that someday it will need to be dismissed and then, well, this is the cheapest option for something not useful for anything else? $\endgroup$ – Adriano Repetti Jan 13 '18 at 12:10
  • $\begingroup$ Yeah. I suppose it could be split into parts and further used, but... $\endgroup$ – PearsonArtPhoto Jan 13 '18 at 15:24

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