Text 4254, 81 rader
Skriven 2006-07-18 16:25:00 av Robert E Starr JR (4726.babylon5)
Ärende: Re: Congratulations NASA
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* * * This message was from Josh Hill to rec.arts.sf.tv.babylon5.m * * *
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On Tue, 18 Jul 2006 20:22:28 +0100, Andrew Swallow
<am.swallow@btopenworld.com> wrote:

>Josh Hill wrote:
>[snip]
>
>> [snip] And
>> some think that having been burned by the troublesome high-tech
>> shuttle they've gone to the opposite extreme and deprived us of the
>> opportunity to continue making progress towards economical reusable
>> vehicles.
>> 
>Any such reusable vehicle will need proper retro-rockets to slow it 
>down.  To develop one try designing a cargo only one to return 1 tonne 
>to the Earth first and scale up.
>
>It would be nice if the engines can be used for both take off and
>landing.  Permanently attaching the take off only engines to the
>landing compartment was a weird design.

>During vertical take off the astronauts do not look out of the
>window, so they can be near the back of the vehicle.  The
>discardable fuel tank can go anywhere, including at the front
>and side.

Problem with using the engines for landing is that you need to carry
the fuel with you, and in an SSTO design you have to carry all the
engines to orbit. Orbital refueling would solve the fuel problem, but
you'd need an extraterrestrial source of fuel, which would be way too
expensive at this point. So for now, more or less conventional TSTO
(or 1-1/2STO) seems to be a more practical approach.

The practicality of reusing the engines depends in general on the cost
of recovering and refurbishing them. You could I think design a very
cool vehicle that would reduce those costs, but then you'd run into
another problem -- there are so few high payload spaceflights that the
design, testing, and factory tooling costs would be higher than the
money you would save.

Which isn't to say I don't think we should have done something of the
sort. We could have built an elegant air breathing first stage/H2+O
second stage reusable TSTO, forex. But it would have been expensive,
like building two systems, and we'd have needed more than one size or
type of vehicle.

Or we could have gone back to the original DynaSoar concept, and
mounted an unpowered winged vehicle on top of a conventional booster.
Or used a lifting body approach of the sort the Russians have been
talking about. As I understand it, the reason NASA didn't go with
these concepts is that capsules are safer, in that they can
accommodate an escape tower which allows separation from the vehicle
early in the flight.

One nice idea -- build attachable boosters that contain fuel tanks,
rocket engines, and small jet engines for return. Lets you recover the
valuable engines while retaining modularity so you can accommodate
different payloads. Here's a Russian proposal:

http://www.buran.ru/htm/strbaik.htm

-- 
Josh

"I love it when I'm around the country club, and I hear people talking about
the debilitating
effects of a welfare society. At the same time, they leave their kids a
lifetime and beyond
of food stamps. Instead of having a welfare officer, they have a trust officer.
And instead
of food stamps, they have stocks and bonds."

- Warren Buffett
                                                                           
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