Changing the ISS's orbital inclination to match the Moon

In summary: But in the long run, the inclination issue is a big one. Changing it would require a lot of propellant, and it's doubtful that it would be economical to expend that much energy. It might make more sense to simply mothball the ISS and use its power to drive a scaled-up ion thruster.What is the practical feasibility of changing the International Space Station's orbital inclination to match the orbit of the Moon?Changing the inclination of the International Space Station would require a lot of propellant, and it's doubtful that it would be economical to expend that much energy.
  • #1
Alec Dacyczyn
31
11
What is the practical feasibility of changing the International Space Station's orbital inclination to match the orbit of the Moon?

Major future missions beyond the Earth-Moon system (ie: space colonization) will likely require in-orbit assembly of components from multiple launches. And anything big going to of from Earth will likely take advantage of the Moon's gravity. So it would make sense for do this assembly in orbits that match the Moons orbital inclination. It would be very handy to have the resources of a space station to do this.

Unfortunately, the ISS was built at a 51deg inclination so that the Russians would get to it from their high latitude launch sites. This is dramatically different form the Moon's 5.14deg orbit. And the ISS is a lot of mass moving very very very fast. So changing its orbit so dramatically would require a heck of a lot of impulse, far too much than would be economical with chemical rockets.

What I propose is to mothball and vacate the station (put it in minimal power mode) and then use the bulk of the power from the humongous solar arrays to drive a scaled-up ion thruster like what was used in the Deep Space 1 mission to gradually affect a shift in its orbit.

How many months or years would this require? I attempted to work out an estimate, but go stick at the orbital mechanics. The biggest problem is that there is not a single correct answer for the mission profile. You could simply calculate the delta-v at the ascending/descending nodes, or you could increase the apogee, change the inclination now using less thrust, and then lower it back down. This bit is beyond by ability to analyze.

Other parts are easy:
- The Deep Space 1 thruster used 2100W to produce 92mN of thrust. That's 43.8mN per kilowatt.
- The ISS solar arrays output 84 to 120 kW. Call it 100kW. Suppose that while mothballed it only needs 20% of that power to maintain itself. And suppose it's in shade about 50% of the time. The resulting budget for thrusters would be about 1.728G watt-seconds per day.
- 43.8mN/kW * 1.728M kW-seconds = about 75,700 Newton-seconds per day of operation.
- The ISS weights about 420 tons and is moving at about 7.67km/s.
- Ignoring added mass, daily delta-v = 75,700N-s / 420,000kg = 0.180 m/s.
- Not I just need to figure out how much delta-v would be required for such a maneuverer.
(Forgive me if I goofed up that math. Physics class was a long time ago)

Obviously, this would take a good long while. Exactly how long, is the question. Since propellant mass isn't the paramount issue, as it was in Deep Space 1, and resupply launches can be done frequently it may be more practical to sacrifice some specific impulse to get more 'ommph' out of the day's energy allowance and shorten the timeframe. This may be a good project to test that VASIMR thruster that they've has been working on.

Does this half-baked idea sound feasible to anyone?
 
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  • #2
Assuming a circular orbit, the delta v for an orbital inclination change is-
##\Delta v_i = 2 v \text{ sin} \left( \frac{\Delta i}{2} \right)##
where v is the orbital velocity and ##\Delta i## is the change in inclination.

Using the velocity and inclinations from your post, a delta v of approximately 6 m/s would be required.
 
  • #3
websterling said:
Assuming a circular orbit, the delta v for an orbital inclination change is-
##\Delta v_i = 2 v \text{ sin} \left( \frac{\Delta i}{2} \right)##
where v is the orbital velocity and ##\Delta i## is the change in inclination.

Using the velocity and inclinations from your post, a delta v of approximately 6 m/s would be required.

It's current orbital velocity is 7.67km/s. Surely, 6m/s is a 2-3 orders of magnitude too low.
 
  • #4
Alec Dacyczyn said:
What is the practical feasibility of changing the International Space Station's orbital inclination to match the orbit of the Moon?

Major future missions beyond the Earth-Moon system (ie: space colonization) will likely require in-orbit assembly of components from multiple launches. And anything big going to of from Earth will likely take advantage of the Moon's gravity. So it would make sense for do this assembly in orbits that match the Moons orbital inclination. It would be very handy to have the resources of a space station to do this.

Unfortunately, the ISS was built at a 51deg inclination so that the Russians would get to it from their high latitude launch sites.

The velocity of a spacecraft or station is a tangent to the orbital path. Any orbit angle will aimed at the moon's orbital path twice per orbit. Why not build the assembly plant at an angle that is convenient for receiving parts launched from Russian?

A station in the Moon's plane would have more launch windows. If your Earth-Moon traffic is heavy enough that you need daily launch windows you can easily build more than one station. The ISS does would not support a dozen employees. There is no room on the ISS for a casino or tourist sporting activities (ping pong might fit).

Alec Dacyczyn said:
Does this half-baked idea sound feasible to anyone?

I think you might like tethers unlimited. [not pear reviewed journal but is a real company with excellent diagrams] They are building momentum exchange tethers and electrodynamic tethers. Neither item requires propellant.

Should also be aware of Kessler syndrome. Instead of trying to keep mass in orbit NASA tries to launch objects in a way that will make them (or their pieces) fall and burn eventually. Satellites carry extra fuel on launch so that they can be de-orbited.
 
  • #5
websterling said:
a delta v of approximately 6 m/s would be required

Sorry, my bad- should have been approximately 6 km/s
 

Related to Changing the ISS's orbital inclination to match the Moon

1. How is the ISS's orbital inclination currently different from the Moon's?

The ISS's orbital inclination is currently at 51.6 degrees while the Moon's is at 5.1 degrees. This means that the ISS's orbit is tilted at a steeper angle compared to the Moon's almost circular orbit around the Earth.

2. What are the benefits of changing the ISS's orbital inclination to match the Moon's?

Changing the ISS's orbital inclination to match the Moon's would allow for easier and more frequent visits to the Moon. This would also make it easier for astronauts and supplies to travel between the ISS and the Moon, potentially enabling longer and more sustainable missions on the lunar surface.

3. How long would it take to change the ISS's orbital inclination to match the Moon's?

The time it would take to change the ISS's orbital inclination to match the Moon's would depend on various factors such as the type of propulsion system used and the current location of the ISS in its orbit. It could range from a few months to a couple of years.

4. What challenges would arise from changing the ISS's orbital inclination to match the Moon's?

Changing the ISS's orbital inclination would require precise calculations and maneuvers to ensure that the ISS reaches its desired orbit without causing any damage. It would also require additional resources and costs to implement the necessary changes.

5. How does changing the ISS's orbital inclination affect its current research and operations?

Changing the ISS's orbital inclination would not significantly impact its current research and operations as long as it is done gradually and carefully. However, there may be some disruption in experiments and communication systems during the orbital change process.

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