https://www.scmp.com/news/china/science/article/3255351/nasas-dream-comes-true-china-plans-build-giant-rail-gun-launch-hypersonic-planes-space

  • SubstantialNothingness [none/use name]
    ·
    4 months ago

    I don't know the answer to your question (unfortunately) but I've run into this idea before, and it seems that it's an idea that has been passed around for many years now including by NASA. As I understand it, one of the perks is that you don't have to carry your fuel and engines - so you don't have to move nearly as much mass. You could launch a satellite with just a protective shell around it. So the magnets don't have to instantaneously exert as much force as the rockets do during their entire burn. I assume these planes would be drones so they might be rather small.

    If the idea is that they're sending up people with railguns then it's simply bullshit afaik. It would have to be rail-assisted and the output would be marginal. (edit: super long barrels have apparently been discussed for human launches [with rockets for later stages], but it appears to be generally considered unfeasible right now.)

    The acceleration even for drones would be mind-numbing. Definitely some bleeding-edge engineering challenges on making something that can survive that. I'm not really well-informed on it so I won't speculate in detail, but I do get the impression that most of those challenges are theoretically solvable with today's science. However it would be a breakthrough for many applied science fields.

    If any nation could do this, imo, it's China. They're really taking the lead in almost every measure right now (including the most important outside of welfare imo - research). It's not their fault if the 5eyes want to fear-monger about falling behind. (It is incredibly aggravating, though.)

    • KobaCumTribute [she/her]
      ·
      4 months ago

      You'd still need engines and fuel onboard, or you couldn't circularize the orbit. The idea is more just get something out of the atmosphere with something that doesn't itself have to be dragged along for the ride, then do the rest of it once you don't have atmospheric drag and you aren't fighting directly against gravity anymore.

      It's kind of the same as the idea of "what if the first stage was a big air-breathing plane that just, like, flew really high and really fast?" that keeps cropping up, just finding a way to make the first part of the process less absurdly expensive.

      But no matter what you can't put something into orbit with a single input of velocity unless that was enough to remove it from the Earth's sphere of influence entirely, because you can't make the lowest point in an orbit higher than the point you're currently at.

      • SubstantialNothingness [none/use name]
        ·
        4 months ago

        I think you could theoretically angle it so that the trajectory leads it to fall into orbit, no?

        Presumably these planes would have some means of propulsion once they were out of the atmosphere, otherwise their usefulness would be very limited. I did say "rockets [...] during their entire burn" but I should have said the lift rockets, which iirc is most of the weight so it's still a big deal. However I agree that in no way would this circumvent the need for propulsion outside of the atmosphere for most intents and purposes.

        Anyway, it's all probably a pipe dream with the upcoming climate change challenges. But the science is fun and apparently some experts consider this more-or-less feasible.

        • MoreAmphibians [none/use name]
          ·
          4 months ago

          Absolutely impossible. The problem isn't the angle, the problem is that orbits are circular. The "orbit" would have to go around in circular motion until until it reaches the point where it exited the railgun (after accounting for the rotation of the earth and all the other nonsense you need to account for).

      • WetBeardHairs@lemmy.ml
        ·
        4 months ago

        I think the next evolution after the raillaunch would be a hybrid engine that breathes air and functions in a vacuum so we could have small SSTO craft.

    • Awoo [she/her]
      ·
      4 months ago

      What if the interior of the railgun accelerator was all a vacuum and the exit point was really really really really tall? So that impact with atmosphere at the exit of the gun was lower.

      • Hexbear2 [any]
        ·
        4 months ago

        This is what StarTram is, the launch system maintains a vacuum. The system won't work without that feature.

      • MoreAmphibians [none/use name]
        ·
        4 months ago

        The problem is that you still need an additional acceleration in order to get into an real orbit. In any theoretical orbit (without an acceleration) you'll always go around in a circular motion until you reach your starting point, if your starting point is in the atmosphere then you'll go around your orbit until you hit your starting point in the atmosphere again. This will obviously cause your orbit to decay. There are a few solutions.

        1. Just use a rocket engine. This is the simplest and most practical solution. Vacuum engines are very efficient and you don't need that much fuel.
        2. Use a skyhook. This is a giant spinning thing in orbit. Your spaceship "grabs on" to an end of a line and takes momentum from the already orbiting skyhook station in order to get in orbit yourself.
        3. You might be able to do something weird with the Moon's gravity in order to change your orbit. This would take a while and you would need a huge velocity from the railgun and your orbit would be very high and probably no circular, but there's no physics reasons it wouldn't work (I think).
        • WetBeardHairs@lemmy.ml
          ·
          4 months ago

          I love the idea of combining the rail launch with a skyhook. Skyhooks always sounded like they would fail due to atmospheric concerns which this would alleviate.