Re: DIY space transport

On Sat, 16 Jul 2005 18:48:44 GMT, Scott Lowther
<scottlowther@xxxxxxxxxxxxxxxxxxxxxx> wrote:

>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.

I'm just hoping that Griffin keeps repeating the engineers mantra,

KISS

Kelly McDonald
.

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