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> The fact that firing it generates high peak power is no more relevant for practicality than the fact that firing a handgun generates high peak power. It's jus

by jjk166 5y ago

> The fact that firing it generates high peak power is no more relevant for practicality than the fact that firing a handgun generates high peak power. It's just combustion. This is not a trivial engineering problem. And in the case of a light gas gun, not only do you need to dump all this energy into a driver to compress the light gas extremely quickly, you also then must bring that driver to a halt extremely quickly without destroying everything.

jhgb 5y ago
I'm not saying that a space gun is simple. But I'm not convinced that it's that much more complicated than a hypersonic centrifuge that provides smaller benefits to begin with. BTW did Quicklaunch even have a driver/piston? I'm not quite sure that it had.
- jjk166 5y ago
  Yeah, quicklaunch actually uses methane combustion to drive the piston, the hydrogen is just the working gas. The whole advantage of light gas guns is that since you don't need your working fluid to do the combustion, you can use gasses with much higher speeds of sound which can thus produce much higher velocities, such as superheated pure hydrogen. I am in total agreement though that spinlaunch is a much worse system though.
  - jhgb 5y ago
    I checked on the Quicklaunch design (https://vimeo.com/29822477 https://vimeo.com/29822477) and the only solid moving mass in the gun is the projectile. So apparently you don't need to "bring [...] driver/piston to a halt extremely quickly" since there is none. They did propose to recover most of the gas by closing the muzzle just after the projectile exit, though. That might be complicated.
    - jjk166 5y ago
      There is a piston. At 2:07 they show a close up of the first stage which they are referring to as the "pump tube", that larger diameter section, where the piston is driven up to speed, pumping the hydrogen into the second stage barrel at high pressure.
      - jhgb 5y ago
        There is no piston. Where do you see one? Did you even watch the video? The whole launch sequence is shown there. There's a pressurized hot hydrogen tank that empties into the barrel. There's no "piston [...] driven up to speed, pumping the hydrogen". The hydrogen flows into the barrel on its own because it has high static pressure at the moment of firing. The presenter literally explains it in detail.

by jjk166 5y ago

jhgb 5y ago

I'm not saying that a space gun is simple. But I'm not convinced that it's that much more complicated than a hypersonic centrifuge that provides smaller benefits to begin with. BTW did Quicklaunch even have a driver/piston? I'm not quite sure that it had.

jjk166 5y ago
Yeah, quicklaunch actually uses methane combustion to drive the piston, the hydrogen is just the working gas. The whole advantage of light gas guns is that since you don't need your working fluid to do the combustion, you can use gasses with much higher speeds of sound which can thus produce much higher velocities, such as superheated pure hydrogen. I am in total agreement though that spinlaunch is a much worse system though.
- jhgb 5y ago
  I checked on the Quicklaunch design (https://vimeo.com/29822477 https://vimeo.com/29822477) and the only solid moving mass in the gun is the projectile. So apparently you don't need to "bring [...] driver/piston to a halt extremely quickly" since there is none. They did propose to recover most of the gas by closing the muzzle just after the projectile exit, though. That might be complicated.
  - jjk166 5y ago
    There is a piston. At 2:07 they show a close up of the first stage which they are referring to as the "pump tube", that larger diameter section, where the piston is driven up to speed, pumping the hydrogen into the second stage barrel at high pressure.
    - jhgb 5y ago
      There is no piston. Where do you see one? Did you even watch the video? The whole launch sequence is shown there. There's a pressurized hot hydrogen tank that empties into the barrel. There's no "piston [...] driven up to speed, pumping the hydrogen". The hydrogen flows into the barrel on its own because it has high static pressure at the moment of firing. The presenter literally explains it in detail.