[ExI] Power satellites

spike spike66 at att.net
Fri May 1 22:11:36 UTC 2009


> -----Original Message-----
> From: extropy-chat-bounces at lists.extropy.org 
> [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of 
> Stefano Vaj
> ...
> In fact, were the earth more massive, it might even be 
> impossible, if I am not mistaken, to achieve escape velocity 
> with chemical-reaction rockets, given that any such fuel 
> would not contain enough energy to lift itself, let alone any 
> useful payload and the necessary vehicle...
> --
> Stefano Vaj

No.  Well, not exactly.  If the earth were more massive, there is not a
point where achieving escape becomes *impossible* but rather it does quickly
approach impractical.  The process is exponential, but with no brick wall
stopping the whole parade.

>...given that any such fuel would not contain enough energy to lift

Keep in mind that *the fuel* doesn't actually need to lift itself.  I think
you meant if the earth were very much larger, we couldn't build a first
stage that could take off vertically.  Even this isn't quite right,
depending on how much one is willing to go to extraordinary lengths.  If we
were willing to fire up a Saturn V to get one kg to LEO, the earth could be
more massive and we could still get there.

The more interesting question, and perhaps the one you were getting to, was

*Is it possible to do single stage to orbit?*

That question is still open.  My best answer is yes it is, but you hafta go
without payload and no humans aboard, if you intend to recover the vehicle.
Without needing to recover the bird, there is not much point in going single
stage, ja?  

I started my career in aerospace weight engineering.  The annual conventions
back then had a side session where the smart guys would present designs for
SSTO and argue if it is possible.  They still repeat the same arguments 25
years later, and the numbers haven't changed appreciably in that time.  My
attitude has been SSTO is possible, but not practical, with chemical
rockets.  The earth is just big enough to spoil the fun.  Lockheeed worked
on it for a while, then abandoned it.


I intentionally stayed off the project, for I never could convince myself
that the X-33 approach would work.  In any case, this much I can assure you:
NASA screwed this project, Lockheeed didn't.  NASA refused to use known,
practical technology, aluminum structure, opting instead to insist on a
composite tank which I am confident wouldn't have worked.  

The reason I know (from bitter personal experience) is one must always take
into account the following law of nature: composite tanks are always more
problems than you anticipate.  Even if you take law that into account and
anticipate more problems than you anticipate, they are still more problems
than you anticipate. 

Keith's pop up and push notion, where (one version) is a chemical
propelled/laser ablation hybrid, might get us there.


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