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> Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up. Orbit doesn't work like that. Getting 200, 300 mi

> Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up. Orbit doesn't work like that. Getting 200, 300 miles up is the easy part - the vast majority of the required energy comes from going sideways at 7800m/s.

Zelizz 7y ago
I think they were suggesting that you could save fuel for once you're out of atmosphere, so that you're not fighting air resistance when you start a burn to get into orbit.
- mikeash 7y ago
  You could save a decent chunk of your fuel this way. Maybe 25% or so. In exchange for that, you have to build your rocket and satellite to withstand 10,000 gees of acceleration and hypersonic flight through the lower atmosphere. And somehow build a rail gun that can fire something the size of an office building.
  - aeneasmackenzie 7y ago
    You use an extremely long track, not high acceleration.
    - mikeash 7y ago
      Hard to do if you’re aiming straight up.
      - CapricornNoble 7y ago
        You'd have to re-purpose something like a deep mining shaft from a diamond mine, then stick a giant rail gun in it, almost like Germany's V-3 cannon[1] but on steroids. [1]https://en.wikipedia.org/wiki/V-3_cannon https://en.wikipedia.org/wiki/V-3_cannon
      - imtringued 7y ago
        No we aren't aiming straight up because we need to get into orbit. We need to go sideways as fast as possible. As long as you're not aiming at the ground you will always aim "up" but not straight up.
        mikeash 7y ago
        “Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up.” Firing sideways could save you much more fuel but also means you’re in the lower atmosphere at much higher speed and for much longer.
chillwaves 7y ago
Could the targeting system account for the sideways movement?
- DuskStar 7y ago
  Do you mean in order to use this as an ASAT or ABM system? In that case, probably - though you'd still need some sort of terminal guidance to actually achieve a hit. If you mean "account for the sideways movement" as "give the satellite the horizontal component of the required orbital velocity" this doesn't work for a variety of reasons - #1 is that the railgun is 2000m/s and orbit is 7800m/s, and #2 is that things going 7800m/s (17450mph) at or near sea level tend to get very, very hot very, very quickly which is not particularly great for railgun projectiles and utterly disastrous for things like solar panels.
charlesju 7y ago
Maybe I should rephrase and emphasize that I think this is interesting not necessarily immediately practical. From what I understand about rail guns, they're not even practical yet to deploy for military ground to ground purposes, let alone to get things into space. I think I'm taking a lot of liberties to imagine a future where we figure out a ton of challenges to get all the engineering to match the theory of making this happen. And in general, I believe we should take an optimistic approach to the future, given that getting humans into space in scale would be a marvelous accomplishment for the human race.

Zelizz 7y ago

I think they were suggesting that you could save fuel for once you're out of atmosphere, so that you're not fighting air resistance when you start a burn to get into orbit.

mikeash 7y ago
You could save a decent chunk of your fuel this way. Maybe 25% or so. In exchange for that, you have to build your rocket and satellite to withstand 10,000 gees of acceleration and hypersonic flight through the lower atmosphere. And somehow build a rail gun that can fire something the size of an office building.
- aeneasmackenzie 7y ago
  You use an extremely long track, not high acceleration.
  - mikeash 7y ago
    Hard to do if you’re aiming straight up.
    - CapricornNoble 7y ago
      You'd have to re-purpose something like a deep mining shaft from a diamond mine, then stick a giant rail gun in it, almost like Germany's V-3 cannon[1] but on steroids. [1]https://en.wikipedia.org/wiki/V-3_cannon https://en.wikipedia.org/wiki/V-3_cannon
    - imtringued 7y ago
      No we aren't aiming straight up because we need to get into orbit. We need to go sideways as fast as possible. As long as you're not aiming at the ground you will always aim "up" but not straight up.
      - mikeash 7y ago
        “Imagine putting one or many of those new Space X internet satellites into a rail gun that goes straight up.” Firing sideways could save you much more fuel but also means you’re in the lower atmosphere at much higher speed and for much longer.

chillwaves 7y ago

Could the targeting system account for the sideways movement?

DuskStar 7y ago
Do you mean in order to use this as an ASAT or ABM system? In that case, probably - though you'd still need some sort of terminal guidance to actually achieve a hit. If you mean "account for the sideways movement" as "give the satellite the horizontal component of the required orbital velocity" this doesn't work for a variety of reasons - #1 is that the railgun is 2000m/s and orbit is 7800m/s, and #2 is that things going 7800m/s (17450mph) at or near sea level tend to get very, very hot very, very quickly which is not particularly great for railgun projectiles and utterly disastrous for things like solar panels.

charlesju 7y ago

Maybe I should rephrase and emphasize that I think this is interesting not necessarily immediately practical. From what I understand about rail guns, they're not even practical yet to deploy for military ground to ground purposes, let alone to get things into space. I think I'm taking a lot of liberties to imagine a future where we figure out a ton of challenges to get all the engineering to match the theory of making this happen. And in general, I believe we should take an optimistic approach to the future, given that getting humans into space in scale would be a marvelous accomplishment for the human race.