I've also never been a fan of the feathering. Both it and the hybrid
were gimmicks that Burt came up with because he didn't trust or
understand liquid propulsion.
On 2018-04-06 16:15, Henry Spencer wrote:
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