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Old November 6th 17, 12:23 PM posted to sci.space.policy,sci.physics,rec.arts.sf.science,sci.astro
Jeff Findley[_6_]
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Posts: 2,307
Default SpaceX BFR tanker as an SSTO.

In article ,
says...


Since we're discussing in the context of the Raptor engine I'll use
estimates for methane engines. I'll use a rocket engine analysis program to
estimate the possible vacuum Isp with methane fuel:

http://www.propulsion-analysis.com/index.htm

The specs of the Raptor in its latest incarnation are given he

https://www.freelists.org/archives/a...Xl97QZZkJ3.jpg

If you use the cited combustion chamber pressure of 250 bar of the Raptor,
but give it an expansion area ratio of 300, possible with altitude
compensation, then the vacuum Isp can be in the range of 390 s according to
the rocket engine analysis program.


That image of the Raptor on freelists.org site is not available. It's
available he

http://spaceflight101.com/spx/wp-con...17-Musk-19.jpg


Sure, it's theoretically possible to do such things. But, SpaceX has
actually been somewhat conservative on how they've approached engine
design. Altitude compensation would add a new facet of "bleeding edge
technology" which would introduce more risk into their program
(especially schedule risk since this is a relatively unknown area beyond
past ground testing).

That and they've long ago decided that a fully reusable TSTO is the way
to go. If they're successful at landing the BFR first stage on the
launch platform, that would eliminate *a lot* of work to get it ready to
fly again. They should be able to inspect it, stack the BFR upper stage
on top, refuel it, and fly it again.

SpaceX hasn't been successful due to using bleeding edge technology.
They've been successful by avoiding bleeding edge technology.

The one thing they did embrace, because they had to, was supersonic
retro-propulsion with liquid fueled rocket engines. They only did that
because their initial "simpler" plan, which was parachute recovery of
first stages in the ocean, quite simply didn't pan out.

Jeff
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