Re: Soyuz TMA-12 faulty

Dale Carlson wrote:
On Thu, 29 May 2008 03:07:51 -0500, Pat Flannery
<flanner@xxxxxxxxxx>
wrote:

Jeff Findley wrote:

It's a given that expendables are more prone to failure than a
reusable vehicle of the same complexity.

Hold it.
"Same complexity"? It's not possible to make a reusable vehicle as
technologically simple as a expendable, as it has to do everything
a
expendable has to do...plus be recoverable. So right there you have
added some sort of recovery system (parachutes, wings, landing
gear, etc.) plus, you have to add some sort of TPS on the
recoverable part that reaches orbit and returns to earth after
releasing the payload.

I'm confused. Isn't this discussion about the Soyuz capsule? The
booster was expendable, and maybe the capsule wasn't reusable,
but it was certainly intended to be recoverable. Might even be
reusable, as a Gemini capsule was, although that wasn't part of the
original intent.

The "capsule" that is recovered is only part of the spacecraft.
Making that reusable would have negligible effect on operations costs
as you'd still be throwing away an orbit module and a service module
on every flight. And even if the reentry module itself is 100 percent
reliable, a failure in a part external to it could still put it into a
flight condition that it could not survive.

The same was true of Gemini--most of the technological guts of Gemini
was in the Equipment Module that was destroyed on reentry on every
flight.

Maybe I'm just not following along closely enough. I'm not sure the
Soyuz spacecraft should be more prone to failure because they are
individually crafted by artisans, and each is a one-off thing with
no
previous experience or testing of the craft. They are essentially
manufactured on an assembly line. Sure, while Atlantis or Discovery
isn't on its "one and only flight to orbit", Soyuz by now should
pretty much be "type certified". Unless something has been altered
in its design or manufacture since the last one, the outcome
shouldn't
change. On the other hand, there's nothing to say that a change in
the processing, and in some aspects "remanufacturing" of our
"reusable" orbiters will bring same results as the last flight. It
seems like the two overlap so much as to not really make much
difference...

You're ignoring manufacturing defects and what's called in failure
analysis the "bathtub curve"--failure rates are high for items fresh
off the line, go down after a period of time, and remain low until
wear, fatigue, and other effects of long term operation start becoming
an issue.

Every experienced delivery pilot has a horror story or two about
things that were wrong with a type certified airplane brand new from
the factory.


--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)


.

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