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**Jeff Findley[_6_]** · June 21st 16, 11:09 AM posted to sci.space.policy,sci.physics,sci.astro

In article om,
says...

On 2016-06-20 21:55, Jeff Findley wrote:

SpaceX has recovered more than one stage. They've recovered four so
far.

If the first one that was recovered isn't the one which will fly first,
it means that it isn't really flyiable without refurb if another stage
is in a better condition.

Wrong. The first one is special, because it was first! It will
eventually go back to their headquarters in California to be permanently
displayed. Considering the amount of flown space vehicles in museums,
this is not at all surprising.

I have no problem with SpaceX taking its time to examine things. But the
fact that no a single stage has been designated for a reflight yet means
nobody should be making claims that "it'd a proven technology, it will
be able to fly 10 times without refurb" etc etc.

It should. There is nothing fundamental about a liquid fueled rocket
stage from an orbital launch vehicle that prevents reuse. It's just
that no one has *tried* all that hard to reuse one, until now.

Advocates of reusable launch vehicle tech have known this since the days
of the X-15 (earlier if you want to count the German rocket powered
fighter experience). It was rocket powered and the three copies which
were built flew so many times, I can never remember exactly how many
flights were made. Between then and now, engines have been repeatedly
fired on the test stand to test and qualify them. There is no
fundamental problem here that needs solving.

Just because there is higher degree of confindece that what SpaceX does
will happen (as opposed to NASA) doesn't mean that it is a done deal at
this point in time.

You're allowed to be a bit skeptical, but at the same time, there really
isn't much reason for it. A SpaceX first stage has to perform several
burns just to complete it's primary mission, then kill horizontal
velocity, then reentry burn, then landing burn. That's already
demonstrating several rapid restarts in the time span of a few minutes!

Since this is all new stuff, SpaceX has to develop validation tests for
those inspections. I am sure it os far mroe involved than looking at the
stage with a flashlight and using some Palmolive and s sponge to clean
off some burn marks.

What "new stuff"? Visual inspections? Validation firings on a test
stand? What do you expect them to do between flights?

Consider the one that landed "leaning". If landing was hard enough to
cause a leg to crumple, they probably have to do more expensive tests to
ensure the rest of the stack is fine since the other legs transfered the
full force of landing.

Possibly, but I doubt it since that's what the crushable inner core is
supposed to do. It wasn't unexpected at all.

And I would suspect that for each flight, they would have high speed
video of launch and several phases to detect any anomalies. Say they saw
something strange on takeoff, but stack landed fine. They will still
want to investigate.

Certainly, but if there had been a significant problem during that main
burn, there would not have been enough fuel left for a landing in the
first place. The landing fuel would have been burnt to make up for any
performance shortfall during the main burn to put the second stage and
payload on the right trajectory. So a successful primary mission is a
very good indicator that nothing serious went wrong.

In fact, the crumpled leg one is likely a good candidate to help develop
inspection/testing procedures since the likelyhood of something being
broken is higher on that one.

Again, possibly. But, pressurized tanks, which make up most of the
structure of the stage, are really freaking strong. As long as they
don't rupture, the stage as a whole is very likely o.k. I'm sure SpaceX
has done analysis and possibly even ground testing for this case and
already know what to expect. No, analysis and ground testing aren't a
replacement for flight testing, but this assumption that a stage might
be bad just because it's been to space and back is ludicrous.

Go re-read the history of the X-15. It was *always* expected it could
be reflown, barring a very hard landing because that was the case with
every aircraft before it! And even in the case of a hard landing, it
could be torn down and repaired. In all the flights of the X-15, only
one was permanently lost because it broke up and was destroyed during
flight.

Somehow, the launch vehicle guys in both the US and U.S.S.R. got a free
pass to ignore all of that experience with rocket engines and flight
vehicles and clung to the mistaken belief that launch vehicles must be
expendable simply because they started their engineering work with
missiles instead of aircraft. Madness. Simply madness.

It's mind boggling to think that it's taken the better part of a century
to start to meaningfully reverse that wrong headed thinking that never
should have existed in the first place.

Jeff
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