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The issue with a gun to get things into orbit is that you need to provide enough force right at the beginning to get into space. That would destroy most anythin

The issue with a gun to get things into orbit is that you need to provide enough force right at the beginning to get into space. That would destroy most anything. So you could shoot something into orbit, but it will be a largely mangled hunk of metal by the end of it. If I were in 1910, trying to get something into space, I'd use a hot air balloon to go a few miles, then shoot a gun. Ideally, it would be done at the equator, where the tangential speeds are higher and getting into orbit is easier.

pg 17y ago
We can deal with mangled hunk of metal problem in version 2. For now I'm just asking whether one could get anything into orbit by shooting it from this gun.
- ivankirigin 17y ago
  Step 1: figure muzzle velocity required to get into orbit. Step 2: make a basic model for air resistance, which feeds back into velocity Step 3: does that feedback converge or diverge? If divergent, impossible. Step 4: make that material I don't know enough aerodynamics to model high speed air resistance well. The way we handle it coming back to earth is to add a layer that will be shed in heat to protect the object. That adds mass.
- lutorm 17y ago
  No, Daniel's right. Or the true answer is yes, any time you throw something up into the air, it's in orbit. It's just that the orbit intersects the Earth's surface. Orbits are (to a good approximation) closed ellipses, so anything shot from the Earth's surface will come back to surface level no matter how fast you shoot it. Another way to think about the problem: An orbit is determined by both the energy and angular momentum of the object. (A circular orbit has the highest angular momentum of any orbit with the same semimajor axis.) From a point injection of these, like from a gun, you can get enough energy but never enough angular momentum to get the perigee higher than the Earth's surface. For that you need some tangential thrust (at a location that's not the apogee). The most energy-efficient way to get into orbit consists of two tangential impulses. The first one raises the apogee to the desired height, the second one is injected at apogee to circularize the orbit. (Though it's strictly only applicable for changes in orbit, not from launches from the ground: http://en.wikipedia.org/wiki/Hohmann_transfer_orbit http://en.wikipedia.org/wiki/Hohmann_transfer_orbit)
- smhinsey 17y ago
  If I was setting out to do it, I'd think about a three part system. First would be the gun on the surface, the second would be a launch vehicle, and the third would be a satellite in orbit to act as a target. The gun fires the launch vehicle at the target. The satellite (I picture it as a donut, with the projectile aimed at the center) uses an electromagnet to "fix" the launch vehicle's orbit. Aside from whatever physics I am ignorant of, I think the big question mark here is power as I would expect the draw of the magnet to be beyond what you could plausibly provide with solar panels. It's also questionable how well this would scale. It doesn't seem like something you would ever think of using to launch crewed vehicles or things like the Hubble, but if the marginal cost of your launches is low, it seems like individual cargo capacity is less important. You could launch raw materials, small parts and assemblies, and maybe even things like human consumables.
  - ivankirigin 17y ago
    The influence of magnetic forces decays at r^2 in distance, making any sort of magnetic tractor beam extremely unfeasible.
    - smhinsey 17y ago
      I'm having trouble explaining it in words, but I'm thinking of it as more of a funnel you aim at than a discrete beam.
- billswift 17y ago
  See my note above - the problem is the need to circularize the orbit so the projectile doesn't just hit the other side of the Earth. EDIT: I just had a thought, if you have a facility in orbit, you could use a gun to shoot perfectly vertically to the orbital height, then capture the projectile before it fell back. Nope, that still wouldn't work - The capturing vehicle would need to add velocity to the projectile to raise its velocity from the eastward component of the radial velocity of the launch site to the orbital velocity.
  - ivankirigin 17y ago
    You've described a Sky Hook. It's a great idea: http://en.wikipedia.org/wiki/Skyhook http://en.wikipedia.org/wiki/Skyhook You're right that you don't want to accelerate it too much when caught. One of the coolest applications of sky hooks is _landing_ when there is no atmosphere. You extend or contract the tether to decrease or increase the angular momentum, and balance it with the decreasing potential energy of landing. You can land softly without rockets.
jacquesm 17y ago
Hard to deal with recoil issues when firing from something that is not anchored. You'd have to have a pretty massive balloon.

pg 17y ago

We can deal with mangled hunk of metal problem in version 2. For now I'm just asking whether one could get anything into orbit by shooting it from this gun.

ivankirigin 17y ago
Step 1: figure muzzle velocity required to get into orbit. Step 2: make a basic model for air resistance, which feeds back into velocity Step 3: does that feedback converge or diverge? If divergent, impossible. Step 4: make that material I don't know enough aerodynamics to model high speed air resistance well. The way we handle it coming back to earth is to add a layer that will be shed in heat to protect the object. That adds mass.
lutorm 17y ago
No, Daniel's right. Or the true answer is yes, any time you throw something up into the air, it's in orbit. It's just that the orbit intersects the Earth's surface. Orbits are (to a good approximation) closed ellipses, so anything shot from the Earth's surface will come back to surface level no matter how fast you shoot it. Another way to think about the problem: An orbit is determined by both the energy and angular momentum of the object. (A circular orbit has the highest angular momentum of any orbit with the same semimajor axis.) From a point injection of these, like from a gun, you can get enough energy but never enough angular momentum to get the perigee higher than the Earth's surface. For that you need some tangential thrust (at a location that's not the apogee). The most energy-efficient way to get into orbit consists of two tangential impulses. The first one raises the apogee to the desired height, the second one is injected at apogee to circularize the orbit. (Though it's strictly only applicable for changes in orbit, not from launches from the ground: http://en.wikipedia.org/wiki/Hohmann_transfer_orbit http://en.wikipedia.org/wiki/Hohmann_transfer_orbit)
smhinsey 17y ago
If I was setting out to do it, I'd think about a three part system. First would be the gun on the surface, the second would be a launch vehicle, and the third would be a satellite in orbit to act as a target. The gun fires the launch vehicle at the target. The satellite (I picture it as a donut, with the projectile aimed at the center) uses an electromagnet to "fix" the launch vehicle's orbit. Aside from whatever physics I am ignorant of, I think the big question mark here is power as I would expect the draw of the magnet to be beyond what you could plausibly provide with solar panels. It's also questionable how well this would scale. It doesn't seem like something you would ever think of using to launch crewed vehicles or things like the Hubble, but if the marginal cost of your launches is low, it seems like individual cargo capacity is less important. You could launch raw materials, small parts and assemblies, and maybe even things like human consumables.
- ivankirigin 17y ago
  The influence of magnetic forces decays at r^2 in distance, making any sort of magnetic tractor beam extremely unfeasible.
  - smhinsey 17y ago
    I'm having trouble explaining it in words, but I'm thinking of it as more of a funnel you aim at than a discrete beam.
billswift 17y ago
See my note above - the problem is the need to circularize the orbit so the projectile doesn't just hit the other side of the Earth. EDIT: I just had a thought, if you have a facility in orbit, you could use a gun to shoot perfectly vertically to the orbital height, then capture the projectile before it fell back. Nope, that still wouldn't work - The capturing vehicle would need to add velocity to the projectile to raise its velocity from the eastward component of the radial velocity of the launch site to the orbital velocity.
- ivankirigin 17y ago
  You've described a Sky Hook. It's a great idea: http://en.wikipedia.org/wiki/Skyhook http://en.wikipedia.org/wiki/Skyhook You're right that you don't want to accelerate it too much when caught. One of the coolest applications of sky hooks is _landing_ when there is no atmosphere. You extend or contract the tether to decrease or increase the angular momentum, and balance it with the decreasing potential energy of landing. You can land softly without rockets.

jacquesm 17y ago

Hard to deal with recoil issues when firing from something that is not anchored. You'd have to have a pretty massive balloon.