3 ms·

The launch mechanism doesn’t have to point straight up; it could point at an angle. Of course that will lengthen the distance traveled through the atmosphere, b

The launch mechanism doesn’t have to point straight up; it could point at an angle. Of course that will lengthen the distance traveled through the atmosphere, but maybe it could still work if the launch vehicle can withstand enough heat.

modeless 5y ago
Doesn't matter what angle you throw it. An object in orbit always returns to its starting point. When the object is released, its orbit intersects the ground (unless it reaches escape velocity). If you want to change the orbit so it no longer intersects the ground, you must impart a huge velocity change to the object after it clears the atmosphere, and the only practical way to do that is to include a rocket engine and propellant and avionics in the payload.
- schoen 5y ago
  That's a very clear argument. Can the effect of air resistance usefully change this, since it's a force acting on the object after it's released? It seems like it's quite bad that the force always points directly opposite the velocity, and I imagine there's a straightforward argument that this can't "improve" the orbit, but I'm not sure offhand how to incorporate that into the analysis.
  - modeless 5y ago
    I think you might be right, the atmosphere might be able to help you a little. However, any orbit you obtained by interaction with the atmosphere would still intersect the atmosphere, and so would decay rapidly. You'd still need a rocket to boost up afterward. Maybe it could reduce the amount of propellant necessary.
  - gizmo686 5y ago
    Air resistance applies a force opposite to the direction of travel (retrograde). At any given instant, the effect is to not change your direction of movement, but decrease your speed of movement. A retrograde force will always lower every point of your orbit (except the exact point where the force was applied, which would remain on your orbit). Since your orbit already has a point that intersects the surface of the planet, your new orbit must also intersect the surface. One minor complication: Technically, air resistance applies a retrograde force relative to the direction of the wind. At low speeds this might actually increase your orbital velocity. However, the speeds where this is relevant are so small that they are not worth consideration.
    - idontwantthis 5y ago
      I wonder if it would somehow be possible to very temporarily decrease air density on the flight path. Heating it or firing a vortex or something.

modeless 5y ago

Doesn't matter what angle you throw it. An object in orbit always returns to its starting point. When the object is released, its orbit intersects the ground (unless it reaches escape velocity). If you want to change the orbit so it no longer intersects the ground, you must impart a huge velocity change to the object after it clears the atmosphere, and the only practical way to do that is to include a rocket engine and propellant and avionics in the payload.

schoen 5y ago
That's a very clear argument. Can the effect of air resistance usefully change this, since it's a force acting on the object after it's released? It seems like it's quite bad that the force always points directly opposite the velocity, and I imagine there's a straightforward argument that this can't "improve" the orbit, but I'm not sure offhand how to incorporate that into the analysis.
- modeless 5y ago
  I think you might be right, the atmosphere might be able to help you a little. However, any orbit you obtained by interaction with the atmosphere would still intersect the atmosphere, and so would decay rapidly. You'd still need a rocket to boost up afterward. Maybe it could reduce the amount of propellant necessary.
- gizmo686 5y ago
  Air resistance applies a force opposite to the direction of travel (retrograde). At any given instant, the effect is to not change your direction of movement, but decrease your speed of movement. A retrograde force will always lower every point of your orbit (except the exact point where the force was applied, which would remain on your orbit). Since your orbit already has a point that intersects the surface of the planet, your new orbit must also intersect the surface. One minor complication: Technically, air resistance applies a retrograde force relative to the direction of the wind. At low speeds this might actually increase your orbital velocity. However, the speeds where this is relevant are so small that they are not worth consideration.
  - idontwantthis 5y ago
    I wonder if it would somehow be possible to very temporarily decrease air density on the flight path. Heating it or firing a vortex or something.