[AR] Re: VSS Unity powered flight
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 6 Apr 2018 16:15:08 -0400 (EDT)
On Fri, 6 Apr 2018, Paul Mueller wrote:
I'm also not clear on what is inherently wrong with their
concept...horizontal launch, reusable first stage (WhiteKnight), suborbital
only, hybrid propulsion, nitrous oxide oxidizer, feathering, horizontal
runway landing? Or a combination of these? Or something else entirely?
I can't speak for Rand, but I would guess it's hybrid propulsion, with a
side order of nitrous oxide oxidizer. :-) The rationale for the choice of
propulsion system was weak from the start, got weaker with a fatal nitrous
accident, got weaker still with all the fuel difficulties they've been
having, and definitely isn't going to hold up well in sustained use.
A nitrous hybrid might perhaps, arguably, have been the preferred way to
win the X-Prize. But anybody's who's got to load a new multi-ton fuel
grain into the vehicle for every flight is not planning for a serious
flight rate. To make money, you *want* a serious flight rate, and that
puts a *big* premium on a vehicle design whose only consumables are
liquids you pour into tanks.
There are some other issues with things like CG management, but the sheer
awkwardness of refueling is probably at the top of the "why big hybrids
are a bad idea for reusables" list.
Henry
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