In article ,
says...

In article ,
says...

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).

A more reusable engine also helps to make qualification testing cheaper.
An engine that can be fired multiple times without tear downs is far
cheaper to certify than one designed to be "expendable" and therefore
needs to be torn down more frequently because the margins are thinner.

Along the same line of thinking...

Here's a quote from Sam Gunderson, Blue Origin business development
manager, in a recent Aviation Week & Space Technology article about the
BE-4 engine:

"The things that are positive about methane and LNG [liquefied natural
gas] are that LNG, being a cryogenic, allows us to really do things
differently. It is closer to the temperature of the liquid oxygen, which
makes it easier to launch the vehicle, and it is about one-third of the
cost of RP-1 [rocket propellant]. Where that really comes in is not too
much in operations, but in the test program," Gunderson says. "There are
a lot of seconds worth of testing that have to go into the program."

Cite:

Blue Origin Fires Up BE-4 Methane-Fuel Rocket Engine
Blue Origin marks successful first hotfire of BE-4 rocket engine
Oct 27, 2017 Irene Klotz | Aviation Week & Space Technology
http://aviationweek.com/space/blue-o...-methane-fuel-
rocket-engine

Blue Origin is incorporating quite a bit of tech in that engine to make
it easily reusable. I believe it's got fluid bearings for the
turbopumps which pretty much eliminates bearing wear, if startup and
shutdown transients aren't an issue.

Again, designing an engine more economic to reuse also means it's more
economic to test fire during its development program. The general
consensus is that it costs about $1 billion to develop a new liquid fuel
rocket engine. Anything you can do to lower that development cost is a
good thing.

Jeff
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