JF Mezei wrote:

On 2017-05-11 08:56, Fred J. McCall wrote:

True. And they still have a higher power to weight ratio than any
other rocket engine, which means they still have to push those things.


If you have an existing very precise design for the SSMEs, I am trying
to understand why you can't automate with current manufactruring
technology which is by far more precise than any human operator.


I'm sure you are trying to understand that. But I don't think you
will because you don't understand how this stuff works.


I am in no way saying that producing an SSME would end up cheaper than a
Merlin. But modern automated tooling should be able to produce parts
that are well within tolerances of the SSMEs an thus make that engine
less outrageously expensive than back in the 1970s when it was first
produced.


But not as much less as you seem to think.


In terms of disposable vs re-usable, if you're keeping same design and
materials, does it make a difference when you build it whether it will
be flown a couple times (tests + 1 flight) versus re-used many many times?


They're not keeping the same materials. That's how they're making it
cheaper.


Any reduction in build quality would severely increase risk of explosion
on the one flight it does (or preceeding test firings), right?


Wrong.


I can understand how reusability comes into play when you design a new
engine from scratch since you have to choose materials and designs that
will last for dozens of hours of firing instead of maybe 30 minutes.


30 minutes is a preposterously long firing time for an expendable
engine.


But if taking an exsiting design that targetted reusability, wouldn't
newly built SSMEs be inherently re-usable even if not intended?


No, because part of the redesign changes materials.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
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