Re: Does NASA save money reusing SRB's?

Scott Lowther <scottlowther@xxxxxxxxxxxxxxxxxxxxxx> wrote in
news:3A%Pe.1005$Xo3.748@xxxxxxxxxxxxx:

>>The other red flag is that solid strap-ons have been used for decades
>>by many other countries (particularly Ariane) and other domestic
>>expendable launch systems, yet nobody else reuses their solids.
>
> Soyuz has launched over 6000 of their strap on liquid boosters, and
> haven't recovered a one. Would they be cheaper recoverable? Dunno. At
> thier flight rate... probably.

If anything your point about Soyuz raises the question whether reuse of
strap-ons *in general* saves money. If it did wouldn't *somebody* in
the world (besides NASA) have at least tried it, after concluding it had
potential during their paper studies? The Soviets spent a staggering
amount of money developing the Energia/Buran system from scratch -- why
didn't they spend a tiny fraction of that at some point to make Soyuz
strap-ons reusable -- amoritized over the *thousands* of Soyuz stage-
flights?

If nobody has done something (reusing stages), it's wrong to say we know
it's a good idea. This is one thing I've grown tired of hearing from
people in the industry as if it's a proven fact (somehow apparently known
by everyone except those who choose never to build them). We have two
data points on reusable space vehicles that have been built and flown:
Shuttle and Buran. While it's true that Buran was cancelled for
cost/benefit reasons, since it was such a blatant copy of the Shuttle I
think we can say it isn't a second independent data point. So that
leaves us with only one data point -- the Shuttle, and we know it was a
failure on cost/benefit. All the other talk of reusable systems are
simply speculation or at best paper studies. For all we know there are
problems common to any reusable system that we haven't identified yet
because we haven't built more than one system to see the pattern.

The fact nobody besides NASA has tried to do it suggests others don't
believe it's a good idea. That's not to say they can't all be wrong
(since nobody tried it), but the fact that many minds from many cultures
have looked at the same issue and come to the same decision is something
we shouldn't ignore.

Personally I think there's more potential for reusing strap-ons than any
other stage, and I hope that somebody actually builds one to get us more
data on their advantages/disadvantages. Odds are it will take several
iterations before we get to something that doesn't have unexpected
problems and comes out ahead on cost, or it may simply prove that
expendables are always cheaper. I hear the Air Force wants to do a
demo, though I doubt they'll have the money as long as we're in Iraq.


> Titan III solids were seriously examined for reusability. Being steel
> cases, that made sense. However, a lot of modern solids are smaller
> and made from composites, like the GEM motors, of which somethign like
> 800+ have flown; the GEMs static test fired on the pad have shown that
> they are *not* refurbishable.

Yes, I figured small solids would be less suitable than large ones for
reuse. That's why I cited Atlas-V and Ariane-V as examples, because
they have large solids. As you point out Titan is also something to
look at, though I chose to use examples of recent designs that are
currently in production.


>>Either you save money by recovering/reusing solid strap-ons or you
>>don't,
>
> Same goes with liquid.

Yes, but with liquids there tend to be a lot more differences in terms of
engine design & cost, stage size, burn time, etc that make blanket
statements about them less appropriate. Strap-on solids have a lot more
in common with each other than their liquid counterparts have with each
other, so we can draw conclusions about solid strap-ons as a group with
greater confidence than we can with their liquid counterparts.

Soyuz, if memory serves, uses peroxide powered turbines to pump storable
propellants in a strap-on application. Titan used storables to power
their turbines and they were 1st stage engines rather than strap-ons.
SSME is a closed-cycle high pressure LOX/LH2 main engine located apart
from its tanks. And so on. My point is that there tends to be a lot
of factors with liquids that complicate apples-to-apples comparisons and
the ability to assess their potential for reusability.


> One issue would be cranking up the productionr ate of the case
> segments. This is non-trivial. I gather the lead time for a new
> segemnt is on the order of *years*.

Yes, I wasn't trying to suggest that it would be trivial for NASA to
switch. "NASA can't change" = might have cost less if chosen from the
start, but future recurring saving don't justify the cost of changing
now, or it is a political impossibility. "NASA won't change" = would
still save money going forward but are too stupid or conservative to make
the right decision.
.

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