Re: DIY space transport

"Scott Lowther" <scottlowther@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:gEcCe.1342$cg.1004@xxxxxxxxxxxxxxxx
>
> 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.

While I agree that the SSME is a bad design, Isp comes after you achieve
low cost, reliability, practicality and T/W, not before. Definitely one
wants to save megabucks by designing as far away from the design edge as
possible, this is what design is about - value for money. But, just
making a rocket bigger to decrease costs is a fallacy.

This is a flight rate type quandary. It is no wonder space is so
expensive when there is this one off mentality to space transport
construction. The first prototype invariably costs twice as much, is
over weight, and works half as well. Prototyping should almost be a
production line with tooling and institutional knowledge being developed
and covered over many vehicles, not just one. Simply opting for a
larger vehicle only makes sense within the one off mentality. Like
flight rate, increased vehicle size reduces the benefits of mass
prototype design and production, the cost and payload benefits of which
can be far more substantial than just making the vehicle larger.

Design often, build often and fly often, within near term markets that
means building small.

Pete.


.

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