[AR] Re: shuttle SRBs (was Re: Re: Phenolic regression rate)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Mon, 5 Feb 2018 12:24:54 -0500 (EST)
On Mon, 5 Feb 2018, Nels.Anderson@xxxxxxx wrote:
Not to mention Starliner (Atlas V 422) or Dream Chaser (552), just in
case you're concerned that politics may be seeping into NASA's analysis
of SLS's SRBs.
Small one-piece solids, especially ones with fixed nozzles, have a rather
better record than big segmented solids. So particularly if you have few
alternatives, it's easier to convince yourself that they're acceptable.
(Right now, if you've got a moderately hefty manned spacecraft to go up on
a US launcher, your choices are few. Single-core no-strapons Delta IV has
less payload and higher cost than no-strapons Atlas. Delta IV Heavy is
impossibly expensive. Falcon 9 might not be available to a spacecraft
that competes with Dragon. SLS is uncertain, unavailable, and not least,
astronomically expensive. So if you want to buy a liquid-only US launch,
then fitting on an Atlas 402 has to be a design priority from the start,
and it may rule out lifting bodies in particular, because they're heavier
than capsules.)
As of a few years ago, the Russians were proposing solids for -- get
this -- parachute-less controlled soft landings of Federatsiya (known at
the time as PTK NP), the proposed new crewed spacecraft. "Throttling"
would be achieved by vectoring motors in pairs to control cosine losses.
The reason for solids rather than liquids was a requirement for one-year
lifetime in orbit.
Soyuz has always used small solids as braking rockets for landing. When
the overall mass ratio is small, it's easy to overbuild the solids to make
them very reliable -- there are passenger airliners certified to use solid
JATOs for rocket-assisted takeoff.
Using them for rocket-only landing seems a bit excessive, though. Surely
one could find a long-lived oxidizer without going that far...
Henry
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