JF Mezei wrote:

On 2017-05-10 18:35, Fred J. McCall wrote:

Uh, what does that have to do with anything? Yes, we could build
bigger and cheaper rocket engines than the RS-25 (and both SpaceX and
Blue Origin are doing so). But those engines aren't RS-25s.

Not what I meant. At the time the SSMEs were built, they pushed the
limits of manufacturing and materials process so very expensive to build.


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.
Part of the redesign is making what changes they can to reduce costs
since the engines don't have to refly, but you can only do so much of
that before you're no longer talking about an RS-25, but some similar
heavier engine.


If, like SpaceX does, you apply moden manufacturing techniques, can't
the cost go down significantlty through the use of automation to create
complex parts with exacting precision?


No.



Engines like RS-25 are still going to require a lot of 'touch labor'.


why?


Because.


If robots build parts with exacting precision, you don't need a human to
use fine sand paper for 2 years to get the thickness just right since
the robot will have done that for you in hours.


Except it doesn't work like that. You're fooling yourself with that
'exacting precision' phrase. There is always some imprecision in the
parts. Without the touch labor on a system that requires very high
precision you will throw away a lot of parts.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn