Jeff Findley wrote:

In article ,
says...
Actually they haven't. Superchilled RP1 drives up costs in order to
improve performance. Going for reusability drives up manufacturing
costs and design costs because you have to make things that can be
used dozens of times without attention (so you need better materials
and tighter designs without pushing for extra performance, figure out
some way to avoid 'coking' on an RP1/LOX engine, etc). It's the
normal engineering evolution of launch vehicles that was stalled while
most payloads were government.


As far as engines go, this isn't really true. All liquid fueled engines
are designed to be fired multiple times, at least on the test stand.
That's how they're qualified. Henry Spencer used to say (paraphrasing
here), there is absolutely nothing fundamental about a liquid fueled
rocket engine that makes it expendable.


Well, actually it is. You go into engine design knowing how many
'refires' the engine needs to stand. If it needs to stand 3 with some
safety margin, the robustness required is a lot less than if it needs
to stand up to 36 of them with the same safety margin. That is going
to drive up manufacturing costs (which you hopefully get back through
the savings by reusing hardware).


Same goes for tanks and plumbing. They pretty much have to be
"certified" for a certain number of fill and drain cycles even if
they're "expendable" in order to account for tanking tests, aborts, and
etc.


And they have to be "certified" for a magnitude (or multiple
magnitudes in the case of something like BFR) more fill and drain
cycles if they're supposed to be reusable.


Solids on the other hand are single use, excepting for complete tear
down to component parts accompanied by extreme cleaning.


Solids are expensive for what they bring to the table when compared to
liquids, even if you fully expend all hardware. I really don't
understand ULA's love affair with them.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw