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Aerospace How do balloon-launched satellites even reach outer space?

  1. Dec 11, 2012 #1
    I recently saw an Elon Musk talk on YouTube where he commented on how if Earth's gravity were just a little stronger, then it would have been impossible to generate enough thrust to get into space. He cited that as the reason why only a handful of national governments have successfully reached space.

    However, I know of a few independent projects involving sending satellites to space via balloons. Peter Forsythe, a British 13-year-old, managed to do it. There's a handful of Kickstarter projects trying to get funding to do the same thing, SkyCube is one example.

    It seems like something isn't adding up. If thrust is a fundamental requirement for reaching space, then how exactly are these balloon-based satellites pulling it off? They surely don't have enough thrust.

    If anyone could clear this up for me it'd be really helpful. Thanks!
     
  2. jcsd
  3. Dec 11, 2012 #2
    Skycube and most of the others launch via rocket (skycube was intended to descend with a balloon -- not ascend). PongSats (Peter's cool experiment) have not gone into 'space' when launched by balloon. The record for any of them is just over 100k feet.

    You cannot get to space by balloon. The maximum altitude you can reach is very 'space like' for a person but still has way too much atmosphere for anything to freely orbit there. Low earth orbit altitude starts around roughly 530k feet.
     
  4. Dec 12, 2012 #3

    berkeman

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    And even if you had a rocket launched from a balloon at high altitude, it might make it high enough to call it "in space", but it will fall right back down to Earth, since it would not have anything close to orbital velocity in the radial direction.
     
  5. Dec 13, 2012 #4

    BobG

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    Even the two communications satellites that were literally balloons were launched by a rocket.

    Echo project

    There's also different definitions for where 'outer space' begins, since the atmosphere actually just gradually tapers off in density.

    About 60 miles is one definition. By that time, the atmosphere is so thin that the speed an airplane would need to generate lift and so on would be greater than the speed necessary to obtain orbit. But, that wouldn't be a functional orbit because, as thin as the atmosphere is, it's still thick enough that atmospheric drag would pull a spacecraft back down to Earth before you'd get any use out of it unless you continuously fired the rocket to maintain an orbital speed.
     
    Last edited: Dec 13, 2012
  6. Jan 18, 2013 #5
    Alot of a rocket's thrust is wasted in accelerating its own fuel, in fighting gravity, and in combatting air drag. These factors compound and feed upon themselves in a circular feedback loop (more needed fuel means even more fuel to accelerate that fuel, etc.) resulting in insanely large rockets.

    By starting out higher (such as with a aballon), you reduce all these factors and therefore you need a smaller rocket to reach space.
     
  7. Jan 21, 2013 #6

    enigma

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    Smaller rocket, sure. Much smaller? Not so much.

    Air drag in the first minutes of launch is almost insignificant next to the 7.75 km/sec orbital velocity.
     
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