Re: Griffin Wants Inline SDLV and 5 Segment SRB/CEV


"Rand Simberg" <simberg.interglobal@xxxxxxxxx> wrote in message
news:42e7eedd.169387997@xxxxxxxxxxxxxxxxxxxxxxxxxxx
> On Sun, 10 Jul 2005 19:07:35 -0400, in a place far, far away, "Murray
> Anderson" <murraya@xxxxxxxxxxxx> made the phosphor on my monitor glow
> in such a way as to indicate that:
>
> >> >It wasn't necessary to have a fly-back booster - just recover the
liquid
> >> >boosters the way the SRB's are recovered.
> >>
> >> That would still have cost more than they had budget for (solids are
> >> cheaper to develop than liquids, honest), and it's not at all clear
> >> how refurbishable a liquid in that class would be after being dropped
> >> in the ocean, Truax's limited experiments aside.
> >
> >They didn't know how refurbishable the solid would be either.
>
> They did, since they don't refurbish it--they rebuild it from the
> recovered segments, with new grain.
>
It's the same with a liquid booster, except for the engine assembly - you
just refill the tanks.
The engine nozzle and gimballing system of the solid are supposedly
recovered and reused, which would be like the engine assembly on the
liquid - except for the turbopump system.
There would be a difference if the turbopump system were harder to protect
from seawater than the gimballing system on the solid.

> >> >So it's cheaper to develop, with large upper stage, than Delta IV
Heavy,
> >> >which already exists?
> >>
> >> Delta IV heavy doesn't have the payload they want, and getting it
> >> (with man rating) probably will cost more than the development of the
> >> Satay.
> >>
> >
> >The payload was supposed to be 25 tons
>
> Emphasis on "was."
>

And the advantage of the stick is what? It doesn't exist so it can't be
demonstrated not to meet the spec until it flies?

> >which could be met or increased by
> >using two RL10's on the upper stage. They'd have to use a shorter nozzle
to
> >fit them both on, but that's nowhere near as hard as developing the upper
> >stage for the stick.
>
> They apparently disagree.
>
> >> >> >Makes the system safer?
> >> >>
> >> >> Well, they seem to think so. Others' mileage (like mine) may vary.
> >> >>
> >> >
> >> >But the belief is so unreasonable that it's hard to take seriously.
It's
> >> >rather like the pre-Challenger failure probabilities for the shuttle.
> >>
> >> Well, they argue that the SRB actually has an excellent reliability
> >> record, and that the failure that caused Challenger wouldn't be a
> >> problem for the stick.
> >>
> >
> >The record is good for solids, and is consistent with the view reported
by
> >Feynman that you can about halve the failure rate with careful selection
of
> >parts. It still has the characteristic of being hard to turn off, and the
> >steering in the proposed booster is more difficult than in the shuttle.
So
> >they're ignoring the downside and emphasizing the upside.
> >As for liquids, they have similar reliability to solids, and higher
> >performance, so the upper stage can be smaller.
>
> Go argue with "them."
>
> >> >> >As for why the shuttle failed so completely to achieve its goals, I
> >> >wouldn't
> >> >> >be so sure I knew the answer.
> >> >>
> >> >> Again, that's pretty well understood, to people who've studied the
> >> >> issue.
> >> >
> >> >I confess to not understanding. I can understand the high fixed cost,
but
> >> >not really why the number of flights is so small, and can't be
increased.
> >I
> >> >accept that they can't do any better but don't quite see the
connection
> >> >between original design decisions and the flight rate. I'm not talking
> >about
> >> >the fantasies of 50 flights a year, but 10-12 a year would have been
very
> >> >helpful after the space station was started.
> >>
> >> Because they didn't design it for rapid turnaround, again due to
> >> limited development budgets.
> >
> >That's a restatement of the problem in other words, together with a
> >rationalization. What was it they wanted to do and didn't have the money
> >for? A better thermal protection system would help, but that wasn't on
> >offer, was it?
>
> With more money, yes. They could have, for example, used a titanium
> structure underneath, instead of aluminum.
>
But the problem is the susceptibility to debris damage, not the insulating
qualities of the tiles. Unless the tiles were all replaced by thermal
blanket and it was less susceptible to damage. Anyway, was that the reason
for using aluminum? I thought it was a combination of manufacturability,
which is more schedule-related, and concern about interference with military
programs.
The leading edges would would still require carbon composite, but that
susceptibility is more safety-related than maintenance related, so wouldn't
impact schedule.

> >Similarly, the external tank shouldn't shed foam to damage
> >the tiles, but what tank design was turned down because it cost too much?
>
> The one that was incorporated into the Orbiter.

That would imply a totally different design, possibly with dense
propellant - and you may well be right about the cost here.

Murray Anderson


.

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