Why does the ISS have to be destroyed?

Question

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.

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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...

Answer 1

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:

• Reusing the US Modules like the Russians plan
• Boosting the ISS and structural Integrity
• How much fuel to deorbit the ISS
• Moving ISS to the Moon
• What would happen if we stopped maintaining the ISS?

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

Don't forget about the more "mundane" reasons, like legal ones. ISS is a large structure that has a lot of potential liability attached to it, and nobody is going to invest money on preserving something that is going to end up as a non-operational burden. Leaving it in a place like the graveyard orbit, even if it was technically "safe", would be like disposing of sensitive classified documents by burying them under one's lawn, instead of properly destroying them by shredding and incinerating the remains.

Answer 6

I believe the solution to salvaging the ISS resides within a plan to dismantle its modules and move them, one-by-one into a more stable orbit wherein they can be reassembled. Granted, this is a piecemeal approach; but it would be similar to the early beginnings of the ISS: Components were sent into space; each at an exorbitant cost and connected to one another over time. The energy required to move individual components from the existing orbit of the ISS would be far less than the payload costs of sending them to space from the surface of the earth. Someone needs to do the math on this, heh?