[SpaceProgram] DARPA-RA-11-70 100YSS Notification

[Atrus]

Except, there really isn't that much difference in gravity from the surface
of the earth, 10km or in orbit.

g on the surface:
http://www.wolframalpha.com/input/?i=solve+%5Bg+%3D+%286.67*10%5E-11+*+5.9442*10%5E24%29+%2F+%286378100%29%5E2%2C+g%5D

g 10km up:
http://www.wolframalpha.com/input/?i=solve+%5Bg+%3D+%286.67*10%5E-11+*+5.9442*10%5E24%29+%2F+%286378100%2B10000%29%5E2%2C+g%5D

ISS orbit (410 km up) :
http://www.wolframalpha.com/input/?i=solve+%5Bg+%3D+%286.67*10%5E-11+*+5.9442*10%5E24%29+%2F+%286378100%2B410000%29%5E2%2C+g%5D

This is why launching rockets on a platform will only make the actual
launch more difficult. You still have to reach escape velocity to obtain
orbit, the only thing you would be doing by launching a rocket at a higher
altitude would be the face that you would have to hit that velocity in a
shorter distance.

Tim Butram



On Mon, Jan 2, 2012 at 7:48 PM, Stuart Young <cefiar at gmail.com> wrote:

> On Jan 3, 2012 11:27 AM, "Atrus" <atrus6 at gmail.com> wrote:
> >
> > What exactly is the benefit of having a high altitude launch platform?
> You would still need to reach essentially the same escape velocity, but
> only have ~half the distance to achieve that velocity. That seems like a
> worse trade off (assuming that your perceived benefit is less air
> resistance).
>
> Benefits (apart from air resistance):
>
> 1. Less gravity to escape (inverse square law).
> 2. Less fuel to carry in the actual rocket (less mass to move to get a
> payload to escape velocity), which should make things simpler (no need for
> multiple stages, simpler avionics).
> 3. Less differences in engine design (high/low atmospheric pressure
> compensation in design not necessary) which simplifies engine and avionics
> design.
>
> And that is just the ones that I can think off of the top of my head.
>
> Btw: Written from my phone, while on site at a client, so pls excuse any
> errors in the text.
>
> --
> Cef
>
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