3 ms·

> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?

by pdonis 2y ago

samstave 2y ago
You sent me down a fun rabbit hole for rail-guns, nano-tubes, super conductors, velocity requirements, megajoules required to launch 1,000KG payload into space: Imagine a U/C channel of carbon nano tube and corresponding super conducting magnets that act as the rail-gun in the same way an aircraft carrier does... (The maths in this thread are pretty cool): You may enjoy this fun short read: https://chatgpt.com/share/616a4cfb-d091-4d09-97a9-e3e7d3e850af https://chatgpt.com/share/616a4cfb-d091-4d09-97a9-e3e7d3e850...
marcosdumay 2y ago
When it's free-floating above the atmosphere and can be as long as you want... sure, why not?
s1artibartfast 2y ago
Yes, that would be the proposal. Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the railgun projectiles start at Vmax and decelerate. Higher altitude would remove much of the friction problem.
- FiatLuxDave 2y ago
  Existing light gas guns can already hit 8 km/s: https://en.wikipedia.org/wiki/Light-gas_gun https://en.wikipedia.org/wiki/Light-gas_gun The biggest advantage of very high altitude reducing the friction problem isn't just that it stops your projectile from turning into plasma, it is that the size of the minimum viable projectile is reduced. People keep focusing on getting people or vehicles into orbit, but the main advantage of a gun-to-orbit system is that the packet size can be made very small. Think machine gun instead of cannon. This means a smaller gun and thus smaller capital investment. Instead of the balloon-supported long gun that mikewarot suggested, imagine a balloon at 30 km altitude supporting a 5 meter long gun and a few tons of both propellant and <1 gram pellets. A target satellite is shot in a long continuous burst, leaving the satellite with a lot more mass and a slightly disturbed orbit. Later shots from a different location and direction can be used to compensate for the added impulse to the satellite's orbit. This could be a cheap way to get a bunch of metal into orbit, or possibly even fuel and oxidizer.
  - pennomi 2y ago
    You want to fire thousands of bullet size pieces of metal into low earth orbit? Holy Kessler Cascade, Batman!
    - FiatLuxDave 2y ago
      While that's not my intention, if you actually wanted to damage satellites and cause a Kessler Syndrome scenario, it's hard to find a system that would have a bigger bang-for-your-buck. I was rather envisioning a target satellite that is designed to absorb the pellet as an inelastic collision. It would probably resemble something like this: https://en.wikipedia.org/wiki/Black_body#/media/File:Black_body_realization.svg https://en.wikipedia.org/wiki/Black_body#/media/File:Black_b... . Of course, if it didn't work as designed, then it could be a problem. The point was that a high altitude low-mass-per-shot gun system could get mass into orbit with a similar energy cost as a space elevator with significantly less upfront capital cost and no need for miracle materials.
- amy-petrik-214 2y ago
  [flagged]
  - batch12 2y ago
    Please use your llm elsewhere.
- pdonis 2y ago
  > Existing ship mounted railguns already shoot projectiles around 3km/s. Projectiles of what mass? And with what acceleration? As I understand it, with feasible railgun lengths the acceleration is well above the limit of human tolerance, and the projectile mass is significantly smaller than a typical payload put into LEO by conventional rockets.
waterproof 2y ago
Yeah, why not? Even if the railgun described was perfectly vertical, it would have 20km of length (vs presumably ~10m max for a military railgun that hits mach 3+). If I'm doing the math right, at 20km of length you need an acceleration of about 160 Gs to reach 8 km/s over that length. Survivable for some payloads. If the railgun is sloped at a 1% grade, it has ~2,000km of length. On that track, a comfy 1.6 Gs of acceleration for 500 seconds gets you up to 8 km/s.

> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?

by pdonis 2y ago

> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?

You sent me down a fun rabbit hole for rail-guns, nano-tubes, super conductors, velocity requirements, megajoules required to launch 1,000KG payload into space: Imagine a U/C channel of carbon nano tube and corresponding super conducting magnets that act as the rail-gun in the same way an aircraft carrier does... (The maths in this thread are pretty cool): You may enjoy this fun short read: https://chatgpt.com/share/616a4cfb-d091-4d09-97a9-e3e7d3e850af https://chatgpt.com/share/616a4cfb-d091-4d09-97a9-e3e7d3e850...

marcosdumay 2y ago

When it's free-floating above the atmosphere and can be as long as you want... sure, why not?

s1artibartfast 2y ago

Yes, that would be the proposal. Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the railgun projectiles start at Vmax and decelerate. Higher altitude would remove much of the friction problem.

FiatLuxDave 2y ago
Existing light gas guns can already hit 8 km/s: https://en.wikipedia.org/wiki/Light-gas_gun https://en.wikipedia.org/wiki/Light-gas_gun The biggest advantage of very high altitude reducing the friction problem isn't just that it stops your projectile from turning into plasma, it is that the size of the minimum viable projectile is reduced. People keep focusing on getting people or vehicles into orbit, but the main advantage of a gun-to-orbit system is that the packet size can be made very small. Think machine gun instead of cannon. This means a smaller gun and thus smaller capital investment. Instead of the balloon-supported long gun that mikewarot suggested, imagine a balloon at 30 km altitude supporting a 5 meter long gun and a few tons of both propellant and <1 gram pellets. A target satellite is shot in a long continuous burst, leaving the satellite with a lot more mass and a slightly disturbed orbit. Later shots from a different location and direction can be used to compensate for the added impulse to the satellite's orbit. This could be a cheap way to get a bunch of metal into orbit, or possibly even fuel and oxidizer.
- pennomi 2y ago
  You want to fire thousands of bullet size pieces of metal into low earth orbit? Holy Kessler Cascade, Batman!
  - FiatLuxDave 2y ago
    While that's not my intention, if you actually wanted to damage satellites and cause a Kessler Syndrome scenario, it's hard to find a system that would have a bigger bang-for-your-buck. I was rather envisioning a target satellite that is designed to absorb the pellet as an inelastic collision. It would probably resemble something like this: https://en.wikipedia.org/wiki/Black_body#/media/File:Black_body_realization.svg https://en.wikipedia.org/wiki/Black_body#/media/File:Black_b... . Of course, if it didn't work as designed, then it could be a problem. The point was that a high altitude low-mass-per-shot gun system could get mass into orbit with a similar energy cost as a space elevator with significantly less upfront capital cost and no need for miracle materials.
amy-petrik-214 2y ago
[flagged]
- batch12 2y ago
  Please use your llm elsewhere.
pdonis 2y ago
> Existing ship mounted railguns already shoot projectiles around 3km/s. Projectiles of what mass? And with what acceleration? As I understand it, with feasible railgun lengths the acceleration is well above the limit of human tolerance, and the projectile mass is significantly smaller than a typical payload put into LEO by conventional rockets.

waterproof 2y ago

Yeah, why not? Even if the railgun described was perfectly vertical, it would have 20km of length (vs presumably ~10m max for a military railgun that hits mach 3+). If I'm doing the math right, at 20km of length you need an acceleration of about 160 Gs to reach 8 km/s over that length. Survivable for some payloads. If the railgun is sloped at a 1% grade, it has ~2,000km of length. On that track, a comfy 1.6 Gs of acceleration for 500 seconds gets you up to 8 km/s.