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

[Luke Weston]

Furthermore, if you want to launch a rocket from some sort of platform
carried by a balloon or something - well, it may be practical to do
this with a small model rocket or something, but it's going to be
highly impractical to carry the weight of any meaningfully large
rocket.

Cheers,
  Luke


On Wed, Jan 4, 2012 at 1:49 PM, Atrus <atrus6 at gmail.com> wrote:
> 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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