13 thoughts on “Ion Propulsion”

  1. I am not sure I see the utility in using them just for tankers unless you are talking about moving fuel for landing on Mars to a fuel depot in orbit there or perhaps at one of the Martian moons.

    For an architecture based on ion engines for human solar system flight, I’d put the departure station at GSO. Use a LEO fuel depot and take people through the VAB’s on chemical rockets. Ion may have low a, but on a long trip the continuous acceleration might get you there faster then just using an initial kick in the seat and coasting on a Hohmann. A side effect is a growing station at GSO that might be usable for a satellite repair and refueling business… using small ion engine vehicles to change to slightly higher or lower orbits and allow one to drift forwards or backwards towards ones customer.

    1. You’re not going to want any of your general-purpose human spaceflight infrastructure in GSO/GEO, because geosynchronous altitude isn’t high enough to be clear of the Van Allen belts. This is a high-radiation environment, and while limited human operations may be tolerable it isn’t the place for people who don’t absolutely have to be there. Satellite repairmen and nobody else, and then only if the satellite repair business alone can justify the cost.

      1. I’m wondering… Since the Van Allen radiation belts are particles trapped in a magnetic bottle, how practical would it be to sweep a wedge surrounding a geostationary platform out of the belts? How big is the cyclotron radius of a typical belt ion at that altitude?

      2. I would send in an ion stage that mates with the satellite and boosts it out of the Van Allen belt to a repair facility, then put it back.

        However, I think repairing a satellite in space at a level that’s more than module replacement is a non-starter unless the repair station has some level of artificial gravity. In zero-G, unscrewing a piece of equipment would inevitably lead to a screw floating back behind a wiring harness. Perhaps it could be extracted with a vacuum cleaner, perhaps not. Of course, the whole thing is just an engineering and production challenge, so if a zero-G station did exist then I’m sure a way would be found to reliably handle the task.

  2. I thought this sentence was stated imprecisely:

    First of all, using ion thrusters means it’ll be a slow trip. Rather than hours, it will take the Boeing satellite months to actually spiral out to its operating altitude.

    The new Boeing 702SP bus satellites will weigh about 2 tons each, about half of the conventional 702 bus satellites with hypergolic propellant propulsion systems. This means that a booster like the Falcon 9 can launch two of them to GTO. The ion thrusters will then gradually increase the perigee and lower the inclination until the satellites are in the final GEO operational orbit. Your description made it sound (to me, at least) like the satellites will be left in LEO and will then gradually spiral out to GEO. That would be a much slower process. It will still take months to achieve the final operational orbit but raising the perigee will get it above the van Allen belts in a matter of weeks. The satellites may still need additional radiation shielding but perhaps not as much as it would if they started in LEO.

    1. I expect PM had a word limit for the article, so Rand couldn’t go into the full-blown explanation. This one covers the main points–ion thrust to final orbit, lots of time in the van Allen belts, hence the need for more hardening. I wonder if the apogee of the initial orbit would be beyond GEO.

  3. Ion engines seem to have a catch-22. You need nuclear power to get the most from them, but if you have nuclear power you don’t need them.

    They may always remain in their niche.

    1. I didn’t see anything in the article about what type of nuke they were talking about. I’m guessing it’s for an ion drive–the article looks like they’re talking high Isp low thrust.

      1. They say megawatt class and they do have some nice ion thrusters already. Whatever type of nuke, the short time frame suggest they don’t think it’s a huge engineering problem.

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