Hopefully, Blue Origin will be solving that problem in a very few years.
On 2018-02-05 09:24, Henry Spencer wrote:
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