[AR] Re: SpaceX Single Stage to Orbit
- From: "John Stoffel" <john@xxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 28 May 2019 16:11:09 -0400
"Craig" == Craig Fink <webegood@xxxxxxxxx> writes:
Craig> On Tue, May 28, 2019 at 7:05 AM Nels Anderson <nels.anderson@xxxxxxx>
wrote:
Craig> On 5/27/19 2:50 PM, Keith Henson wrote:
The not-so-obvious thing they do is using the wings to unload gravity
drag. They do this even after the switch to rocket mode. The wings
save an incredible amount of delta-v compared to a rocket that took as
long to get to orbit.
Craig> How incredible could the savings be? Total losses, not just gravity,
Craig> for a conventional rocket to LEO might be 1000 m/s out of a total
ideal
Craig> delta-V of about 9000 m/s. Saving a significant fraction of that
1000
Craig> m/s ain't peanuts if you're operating well into the rocket equation's
Craig> exponential regime, where a rocket-powered SSTO . But given how
lousy
Craig> hypersonic L/D's, I would think it's almost as much a matter of
trading
Craig> gravity losses for drag losses as saving gravity losses.
Craig> Gravity Losses are a function of Time, so flying to orbit with
Craig> an air-breathing engine is going to be acceleration limited
Craig> along the way. Meaning more time spent doing it. But as the
Craig> vehicle gets closer and closer to orbit, the amount of lift
Craig> necessary to offset the "Effective Gravity" goes to zero at
Craig> orbital insertion.
Craig> Effective Gravity = GravityEarth - CentripetalForce
Craig> So, the faster the vehicle flies, the required lift decreases
Craig> to zero at insertion.
Craig, can you please show your math that makes you believe that
flying to orbit in an air breathing jet is possible? What is your
craft using for air at 50 miles of height? And what speed are you
going at that height?
Have you looked at the Perlan 2 glider that was flying at 70,000+
feet? How about the SR-71? How come the black bird couldn't fly
higher or faster? Can you explain your numbers?
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