Well the ISS does its orbital maneuvers using docked spacecraft usually (though it can also use its own engines in the Zvezda module), and doing enough of the same would get you enough delta v to get to the Moon's orbit eventually, one gentle nudge at a time. The somewhat fragile structure of the ISS doesn't matter here if the nudges are gentle enough.

Sso would depend on the fuel capacity and capabilities of those spacecraft, and whether they can keep supplying it as it gets further from the Earth.

Typically it boosts a couple of meters per second a month.

How does the International Space Station maintain its orbit and what propellant does it use?

Delta v to get to low Moon orbit from LEO is 4.01 km / second

Delta-v budget

The ISS orbit is highly inclined

I'm not sure if you need to change inclination to get to a lunar orbit, would just end up in a highly inclined lunar orbit.

DO YOU NEED TO CHANGE INCLINATION TO AN EQUATORIAL ORBIT TO GET TO THE MOON?

Unless I'm missing something there. I can't think of an example in practice of a spaceship entering orbit around the Moon or another planet or moon at a high inclination like this.

But theoretically, don't see why you need to change inclination to match the Moon.

The two orbits, the orbit of the Moon and the orbit of a highly boosted ISS would intersect, because any pair of orbits intersects in two places.

Of course wouldn't make it a circular orbit same as the Moon before you rendezvoous. That's possible but wasteful of fuel.

Instead use a elliptical orbit. And arrange so the major axis is in the equatorial plane. Do that - an elliptical orbit inclined, but with major axis in the equatorial plane - and eventually that orbit will intersect the lunar orbit.

You'd do that by boosting at the opposite side of the Earth from the point in its orbit where you plan to rendezvous with the Moon.

Boost each time when the ISS is crossing the equator at perigee - that would keep the perigee low (boosts don't make any difference to the altitude at the point in the orbit where you do the boost) - and raise the apogee.

Because you do your boosts when it crosses the equator - the apogee diametrically opposite in the orbit would also lie in the Earth's equatorial plane.

And when raised high enough then the Moon would intersect it.

Then when that happens, then at some point the moon will be in the right place to capture the ISS with a small delta v to go into capture orbit, -then more delta v to lower and circularize to low Moon orbit.

And you aren't aiming for a rendezvous with the Moon, just an orbital insertion, using gravity of the Moon.

So, is very different from e.g. trying to dock one spaceship with another at a different inclination which you can't do without use of a lot of delta v.

It probably wouldn't be a stable orbit, inclined like that - not sure - some inclined orbits are stable, but the Moon I think is basically spherical unlike Earth so probably would then be gradually perturbed by the Earth and Moon gravity, and flatten out into the plane of the Moon's orbit.

(I'd appreciate corrections from anyone expert in orbital maneuvers as it's a tricky subject I know).

FUEL NEEDED - AT LEAST 143 PROGRESS M1S LOADED WITH FUEL TO CAPACITY

So - well anyway - assuming for now that no extra fuel is needed for inclination changes or Moon orbit capture for an inclined orbit like that - if it just used the same amount of fuel it does for normal station keeping - doubled them to start with but would soon leave the Earth atmosphere - so it goes into higher and higher orbit, then that's 2000 months or 167 years to get to LLO (Low Lunar Orbit).

The Progress M1 can carry 1,950 kg of fuel, and 2,230 kg of cargo, total of 4180 kgs if it is all devoted to fuel.

Progress (spacecraft)

ISS uses 8,000 pounds of propellant a year or about 3,600 kg for station keeping.

Higher Altitude Improves Station's Fuel Economy

So - lets suppose an entire Progresss M1 carried only fuel to the ISS. Then that's enough for 1 year of thrust (roughly), so that's a delta v of about 24 m/second.

Anyway that single load of a Progress M1 is clearly nowhere near enough to get it to the Moon. After all it needs 167 years of this not just one year, to get there.

So in total, 167 years at 3600 tons a year, that's 601 tons of fuel. Around 143 of the Progress M1s.

(This is a rough calculation - hopefully in the right ballpark)

I think in principle could be done, with enough rocket launches.

By sending several Progresses a year - you could do it within a few decades even. But would be expensive and require a huge number of launches to do it that way.

NEED TO BOOST THE FUEL AS ISS GETS TO HIGHER ORBITS

As it goes higher then you would need to send more of them, because more fuel would be needed just to boost the Progress itself to reach the speeds needed to rendezvous with the ISS

Although in an elliptical orbit with perigee not much changed from its present one, the speed at perigee would keep increasing in order to make the apogee further from the Earth. So the Progress would need to accelerate to catch up with the ISS.

Eventually probably would send them in pairs, with one Progress acting as a kind of a final stage to boost the other one up to the ISS as it gets faster and faster with apogee higher and higher.

The ISS itself is only around 419.5 tons so the 601 tons of fuel would outweigh the ISS if I've got that right. Facts and Figures

So - anyway not sure it is worth working it out in detail, but you'd need a fair bit more than 143 of the Progress launches.

LIFETIME OF THE ISS

But there's another thing to consider, that in the harsh conditions of space, the modules only have a lifetime of a few decades, before they deteriorate too much - things like structural weakness due to the continual changes of temperature between day and night, cracks beginning to form etc.

So beyond 2020, then the ISS most of its modules will be de-orbited though some of the newer ones, a couple of Russian ones might be saved and used for a new space station. Unless you sent a Soyuz M1 every few days, it would take so long to get it to the lunar orbit that by the time the current ISS got to the Moon it would be no longer usable for human habitation.

Probably better to have rockets with somewhat higher lift capacity to build a station in LLO. But the ISS also is huge, and you could have a small station in LLO with current technology.

So not too likely with current technology. But it’s a little hard to look forward to the 2020s - maybe we’ll have the capability to do it more easily then? Perhaps as a “museum exhibit” - if that seemed likely, we could boost its orbit first to a higher orbit, still LEO but high enough to postpone its demise for some decades - and then a few decades later hopefully have developed the capability to move it anywhere we want in the Earth Moon system. So if you are really keen to preserve it, well boosting it by a few hundred kilometers to put off the end - that could be worth doing. But is it worth spending millions of dollars to do that, just for a museum exhibit?

WORKED OUT PLANS TO BUILD A NEW STATION AT L1 (A LITTLE SMALLER THAN THE ISS)

Usually the idea is to build it in the L1 or L2 positions. Because those are very close to the Moon, and are stationary above its surface, and though they are technically unstable positions in the gravitational field of Moon and Earth in practise you can do station keeping there with hardly any fuel because spacecraft placed there don't just drift away from it but instead tend to perturb around it in a kind of a spiral so you would just "orbit" around the L1 or L2 positions with occasional station keeping thrusts. Also interestingly, it is easy to get from L1 to L2 with hardly any fuel so you can go back and forth between near and far side of the Moon pretty easily also if you ever want to or need to.

This is a plan to build a station in the L1 position from 2001, which would be built by assembly at ISS orbit and then boost to LLO, it's a student design project from the University of Maryland

Clarke Station - slides - PClarke station - article
ENAE 791 - Spring 2004 - Course Syllabus

Here is a more recent plan which involves four three person missions every year to build it and keep it operational, a bit like the ISS, three months for each mission

Human operations beyond LEO by the end of the decade: An affordable near-term stepping stone

BEST TO DO SOME MORE RESEARCH IN LEO FIRST, GEMINI STYLE

I think myself that it might be a good idea to work on closed system habitats first, and artificial gravity, which we could do in LEO.

That would be like the Gemini missions that they did before Apollo, testing the technology they need in LEO before sending it to the Moon.

This time the reason would be because there is so much we don't know about how humans can live and be healthy in space.

Rather than just do a copy of the ISS, which we know how to do, in LLO - why not first see if we can get a closed system habitat working in LEO?

See if a Biosphere II style habitat with lots of plants in space work for removing the toxic chemicals like methane, hydrogen sulfide, etc, and for at least some of the CO2 scrubbing, if they could take place of some of the complex machinery in the ISS (with them as backup)?

And more recycling of waste than in the ISS?

Doesn't have to be perfect, just some of that.

ISS hasn't explored that way of doing things at all, just a few plants in experiments, but not at all the idea of plants throughout interior of the station like Biosphere II.

Plus some generating of food from plants, e.g. tomatoes etc. in space - would cut down a fair bit on supply from Earth.

It may seem "way out" to do that in a space station like the ISS.

But Mars One and SpaceX are talking about doing just that on Mars. Obviously far easier to do that in LEO than on Mars (and the Mars soil really has no significant benefits here, plants can grow in hydroponics, or using aeroponics). So if we think it might be possible on Mars, why not try it in LEO?

Or - if that is too big of a leap - or has technical difficulties - at least - try using algae to generate oxygen. The Russians have shown that you can generate all the oxygen from algae from a surprisingly small space - so why not fly that technology and see if it works in space?

And at the same time - work on artificial gravity. If we can use artificial gravity then we can have humans living in space for years on end - and that's a huge saving, if you only need to transport the humans every few years rather than every three months.

And if you don't need to send them fuel or water or oxygen every few months either, it might become almost as easy almost to live in space long term as in Antarctica.

Not need to go all the way, to a totally closed habitat, and perfect health for the astronauts so they can live there for decades on end.

If we can be just a bit better at recycling, and some element of artificial gravity to increase the time that humans can spend there comfortably from a few months to several years - might make a huge difference at distance of the Moon. Can continue with the rest of the research in L1.

There are several simple experiments we could do in LEO that would totally change decisions about best design for a station at L1, so seems to me best to do that first.

Even - just a couple of years of that would be enough to make a big difference.

So - a couple or so "Gemini style" early test missions to test closed system habitats in space and using algae for oxygen, and have a go at a more extensive closed system with large plants and growing food like tomatoes etc. Perhaps send up unmanned, monitor, then send humans up to them afterwards. Or - just build in lots of redundancy, so you have complete ISS type environment control but then try to gradually substitute more and more of it with plants and algae while keeping the ISS type system for backup in case of emergency.

Then, as for artificial gravity, then simply tethering a TMA to its final stage would let you do experiments in artificial gravity that might totally change your ideas about what the best design for the station is, and you could get a mission like that underway within a few months with political will to do it.

But if we wanted to build a more or less copy of the ISS style space station at L1 or in LLO I think we could do that within a decade using a budget probably not that different from the ISS though result a bit smaller.