Re: DIY space transport

Kelly McDonald wrote:

On Sat, 16 Jul 2005 13:08:06 GMT, Scott Lowther
<scottlowther@xxxxxxxxxxxxxxxxxxxxxx> wrote:



Pete Lynn wrote:



I note that with the similarly inspired SpaceX Merlin, (a very nice
engine by the look of it), ISP is still quite low, (~304 vacuum ISP).




Isp is over rated. It's cost per pound that matters, not pounds of payload per pound of vehicle. Having a reliable engine with decent but unimpressive Isp that you can run and run and run with minimal worry or maintenance would be a hell of a good thing to have. The Saturn Ib's H-1 engine was really quite depressing as far as Isp... but it was not only inadvertantly reusable, it was reusable after dumping in salt water and having two guys tear apart, clean and hose down with WD-40 over the span of a work week or so.




The SSME is a prime example of this. Performance at the cost of
everything else.

Indeed. For Shuttle derived, I've been seeing prices of 90 *MILLION* dollars a pop (about four-five times the cost of an RSRM), with special "expendable" SSME's runnign about $30,000,000. After some investigation (i.e. asking someone who knows more than me), it turns out that the sole difference betweent he expendable and reusable SSME is... paperwork. Exactly the same production line, same drawings, materials, everything. Just $60,000,000 more paperwork.

It seems a lot of people in the know consider the RS-68 to be a pig, due to it's lower Isp. You know what? Who gives a rats ass. If it takes a slightly bigger vehicle and more propellant to get to orbit with the same payload... I'll choose RS-68 over SSME any day. Stretching a core stage costs almost nothing. The cost of additional propellant is trival. But saving *dozens* of megabucks per engine seems like the way to go.



--
"The only thing that galls me about someone burning the American flag is how unoriginal it is. I mean if you're going to pull the Freedom-of-speech card, don't be a hack, come up with something interesting. Fashion Old Glory into a wisecracking puppet and blister the system with a scathing ventriloquism act, or better yet, drape the flag over your head and desecrate it with a large caliber bullet hole." Dennis Miller
.

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