[AR] Re: Flying to Orbit with Hydrogen?
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 18 Dec 2019 15:27:34 -0500 (EST)
On Wed, 18 Dec 2019, John Stoffel wrote:
Henry> Using an EELV instead meant [X-37] could go up inside a payload
Henry> fairing, eliminating the aerodynamic and structural issues.
I wonder if launching a pair of them belly to belly on something big
would let you get away from a fairing? The loads *might* balance out,
though I could see some funky issues...
You'd still have problems with things like gust loads -- crank in enough
angle of attack, and both sets of wings will be pushing the same way.
...the Atlas would normally launch a pretty lofted trajectory, and the
Centaur Single RL-10 would then do most of the horizontal boosting to
achieve orbital velocity. Which honestly does seem to not make sense,
since the *key* metric is orbital (horizontal) velocity as soon as you
can get above a good fraction of the atmosphere. Esp since the Atlas is
just dumped into the Ocean.
Remember that the normal Atlas V configuration is optimized for launch to
GTO, not LEO. Yes, its upper stage doesn't really have enough thrust for
an optimal ascent to LEO, but this is more than balanced out by lower dry
mass (and hence better mass ratio) for the final push to GTO. The whole
reason why the DEC (Double Engine Centaur) configuration existed was to
provide better performance for launches to LEO; the reason nobody's yet
flown a DEC (that I'm aware of) was that LEO customers have been few, and
none of them has needed absolute maximum payload, so nobody was willing to
pay a bit extra to get DEC up to flight status.
Even two RL10s probably is less thrust than you would really like for an
Atlas V second stage for LEO. Most likely the trajectory is still lofted
some, to give the Centaur extra acceleration time before it falls out of
the sky. But doing anything about that -- either a major RL10 upgrade, or
a stage redesign for more than two engines -- would run up the price a
lot. And it's at least better than the single-engine version.
Henry
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