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How fast do we have to go if Earth had no atmosphere?

  1. May 21, 2015 #1
    how fast do we have to go if earth had no atmosphere?
    i'm wondering why don't they send a small, but extremely fast projectile in front of the rocket, which heats and expands the air in front which reduces most of the friction? (maybe like a railgun?)
    does that not reduce the cost?

    or am i being really stupid?
     
  2. jcsd
  3. May 21, 2015 #2

    Drakkith

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    Staff: Mentor

    First, the projectile would be much too quick for the rocket! The rocket starts off at a standstill and only reaches a maximum acceleration of a few g's. This means it takes several minutes for it to reach orbital velocity, while a projectile would be at maximum speed the moment it leaves the barrel.

    There are other issues too. In general it just wouldn't work.
     
  4. May 21, 2015 #3
    because of conservation of energy, the energy you use for rising a rocket into the space is the same as the method you mentioned. Basically the idea is that, you still need same work done to push away those air molecules.
     
  5. May 23, 2015 #4
    The principle you suggest is used on new ships when compressed air is injected all around the vessel for air bubble lubrication. This reduces the drag substantially.

    The problem with a rocket as i understand would be that air as a medium is already very light. "Heating" the air away sounds inefficient to me
     
  6. May 24, 2015 #5
    Terminal velocity = 176 ft/sec. Use that to figure out the drag on the moving object, but that drag would be what you would need to generate to maintain a constant velocity with no acceleration.
     
  7. May 24, 2015 #6

    Drakkith

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    Staff: Mentor

    Why would you want to maintain zero acceleration?
     
  8. May 24, 2015 #7
    energy conservation
     
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