[AR] Re: Falcon Heavy use cases
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Thu, 8 Feb 2018 11:04:47 -0500 (EST)
On Wed, 7 Feb 2018, John Schilling wrote:
1. It is foolish to use anything but cheap, dense propellants in your
Earth launch stage... 2. It is foolish to use anything but LOX/LH2 for
your orbital insertion stage... 3. It is foolish to use different
propellants on different stages... ...Elon has made his choice...
And given that Falcon 9 gets a substantial payload to GTO or a Mars
trajectory with two stages of LOX/kerosene, and that we've just had a
demonstration of how to get bigger payload and/or higher delta-V by just
piling up more LOX/kerosene, I'd say the case for rule #2 is really a
trifle weak...
*Provided*, that is, that you're designing the whole vehicle and there are
no externally-imposed size constraints. LOX/LH2 looks much more appealing
if you're trying to add an upper stage to an existing first stage, because
that limits upper-stage mass, and LOX/LH2 definitely delivers more
performance per kilogram (maybe not per dollar, but per kilogram, yes).
Some of the LOX/LH2-upper-stage fixation from the 60s came about because
both Centaur and the Saturn upper stages (as originally conceived) were
being added to existing boosters (Atlas and Saturn I respectively).
Another example is that LOX/LH2 is really appealing for air launch, where
(unless you feel like spending a *lot* of money and time on aircraft
development) your rocket is tightly constrained by what an existing
carrier aircraft can lift.
Henry
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