Does a solid-fuel Ares 1 make sense?

h (Rand Simberg) wrote:

On Fri, 8 Sep 2006 22:22:22 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

SRBs were chosen for the shuttle on the assumption that thrust termination
*was* feasible in an emergency. Unfortunately, the decision was not
revisited when it became clear that the orbiter and ET were too fragile to
survive SRB thrust termination. (One of several times in the shuttle
program when it was deemed politically infeasible to rethink the design
despite changes in underlying assumptions.)

A feature that disconcertingly seems to be repeated in the current
Ares program...

I don't think that's necessarily the case. Ares has a capsule with
escape tower at the top of the stack; STS has an orbiter and fuel tank
sitting between a pair of SRBs. A top-sitting Orion capsule wouldn't be
quite as susceptible as a Shuttle orbiter is to the nasty side effects
of a solid-fueled booster being ripped open.

In article ,
Alan Anderson wrote:
SRBs were chosen for the shuttle on the assumption that thrust termination
*was* feasible in an emergency. Unfortunately, the decision was not
revisited when it became clear that the orbiter and ET were too fragile to
survive SRB thrust termination. (One of several times in the shuttle
program when it was deemed politically infeasible to rethink the design
despite changes in underlying assumptions.)

A feature that disconcertingly seems to be repeated in the current
Ares program...

I don't think that's necessarily the case. Ares has a capsule with
escape tower at the top of the stack...

I think Rand is referring to the sentence in (), not the specific example
preceding it. The Ares designs have drifted steadily farther away from
the original concepts, as one assumption after another has proved invalid
and required changes, but apparently nobody has stopped to consider
whether it might be better to tear them up and start over.

For example, it's increasingly clear that it's really rather difficult to
build a CEV launcher by putting a LOX/LH2 stage on top of an SRB. The
original rationale for doing that -- doing the new launcher quickly using
existing hardware -- has largely disappeared, as the difficulties have
required switching to new versions of one item after another, but every
new revision is still required to preserve that increasingly-unappealing
basic approach.
--
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On Sat, 09 Sep 2006 23:29:38 -0400, in a place far, far away, Alan
Anderson made the phosphor on my monitor glow
in such a way as to indicate that:

(Rand Simberg) wrote:

On Fri, 8 Sep 2006 22:22:22 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

SRBs were chosen for the shuttle on the assumption that thrust termination
*was* feasible in an emergency. Unfortunately, the decision was not
revisited when it became clear that the orbiter and ET were too fragile to
survive SRB thrust termination. (One of several times in the shuttle
program when it was deemed politically infeasible to rethink the design
despite changes in underlying assumptions.)

A feature that disconcertingly seems to be repeated in the current
Ares program...

I don't think that's necessarily the case. Ares has a capsule with
escape tower at the top of the stack; STS has an orbiter and fuel tank
sitting between a pair of SRBs. A top-sitting Orion capsule wouldn't be
quite as susceptible as a Shuttle orbiter is to the nasty side effects
of a solid-fueled booster being ripped open.

I was speaking much more generally.

"Brian Thorn" wrote in message
news
It was sold as "safe, simple, soon" and is now none of the above, I
guess I'm just a little irritated by the bait-and-switch routine.

As you should be. It's the same game NASA played to complete development of
the shuttle. It never achieved the flgiht rate it should have. It's
initial payload capacity, measured in payload mass, was horribly short of
the value advertized. And because of the previous two shortcomings, it's
cost per flight (including fixed costs) was far higher than what was
originally advertized.

So basically, we're dooming Constellation to future high operational
costs for just one reason: to keep SRB, a booster almost no one thinks
is good for humans or expensive payloads, alive.

Its not worth it.

That was my opinion from the beginning, even without the bait and switch.
We don't need another NASA specific launch vehicle that's designed, built,
and operated by NASA unless we want to repeat the mistakes of the past.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

(Henry Spencer) wrote:

Alan Anderson wrote:
SRBs were chosen for the shuttle on the assumption that thrust termination
*was* feasible in an emergency. Unfortunately, the decision was not
revisited when it became clear that the orbiter and ET were too fragile to
survive SRB thrust termination. (One of several times in the shuttle
program when it was deemed politically infeasible to rethink the design
despite changes in underlying assumptions.)

A feature that disconcertingly seems to be repeated in the current
Ares program...

I don't think that's necessarily the case. Ares has a capsule with
escape tower at the top of the stack...

I think Rand is referring to the sentence in (), not the specific example
preceding it...

I'd have expected to see the word "pattern" instead of "feature", but
you're right:

h (Rand Simberg) wrote:

I was speaking much more generally.

I agree wholeheartedly with Henry's longer description of the tendency
to stick with a design even after many of the assumptions that favored
that design have been revised and even negated.

On Sun, 10 Sep 2006 13:19:50 -0400, in a place far, far away, Alan
Anderson made the phosphor on my monitor glow
in such a way as to indicate that:

(Henry Spencer) wrote:

Alan Anderson wrote:
SRBs were chosen for the shuttle on the assumption that thrust termination
*was* feasible in an emergency. Unfortunately, the decision was not
revisited when it became clear that the orbiter and ET were too fragile to
survive SRB thrust termination. (One of several times in the shuttle
program when it was deemed politically infeasible to rethink the design
despite changes in underlying assumptions.)

A feature that disconcertingly seems to be repeated in the current
Ares program...

I don't think that's necessarily the case. Ares has a capsule with
escape tower at the top of the stack...

I think Rand is referring to the sentence in (), not the specific example
preceding it...

I'd have expected to see the word "pattern" instead of "feature", but
you're right:

I was using "feature" in the sarcastic sense, as in "it's not a
bug--it's a feature!"

Henry Spencer wrote:
In article ,
Jeff Findley wrote:
Actually, you can install thurst termination systems on the SRB. The ones
installed on the shuttle unzipper the casing along the length.

Cutting through the euphemisms, that's a destruct system, not merely a
thrust-termination system.

Unfortunately this event would be extremely violent. So some here do say
that you can "turn off" the thrust of a large SRB...

It's feasible -- it was done for the original Titan SRBs, because the
payloads there were originally going to include Dyna-Soar -- but even a
system meant just to terminate thrust does tend to be a bit violent.

SRBs were chosen for the shuttle on the assumption that thrust termination
*was* feasible in an emergency. Unfortunately, the decision was not
revisited when it became clear that the orbiter and ET were too fragile to
survive SRB thrust termination. (One of several times in the shuttle
program when it was deemed politically infeasible to rethink the design
despite changes in underlying assumptions.)

...design the CEV such that it could survive thrust
termination. The obvious way to do this would be to first fire the escape
tower, and then the thurst termination system.

That's essentially what was planned for Titan and Dyna-Soar -- the
thrust-termination system was purely to keep the launcher from catching up
to an escaping Dyna-Soar.

Unfortunately, the Titan program showed us that there are failure modes of
large, segmented boosters that give little to no warning before the things
violently destroy themselves...

Unfortunately true.

Hmmm, Henry? I asked about such failure modes a while back. You
responded (Thank you), but the inclusion here of the reference to
segmented SRBs now leads me to wonder if your response actually covered
the issue I had in mind. Would a one piece Shuttle type SRB be far less
apt to have such catastrophic failure as, for example, the infamous
Titian event? Are there other catastrophic failure modes even for a
single segment?

One reason I ask is I recall AeroJet, after the Challenger disaster and
a call for an advanced SRB, proposed a single pour design to do away
with the rubber gaskets that failed. IIRC, they actually wanted to dig
out pits at KSC and pour right there. They'd pour, let cure, do void
detection in situ, and extract the resulting SRBs.

It does seem, all in all, that solid rockets don't involve all that
much more danger. Especially if the segments are properly tested and
aren't stored for excessive periods before use.



Also, Aries I requires a roll control package for the SRB...

This is largely a non-issue. Such things are routinely done as minor
upgrades to existing launchers (e.g., in the transition from Atlas I to
Atlas II, such a package was added; it went away again on Atlas III).
It's pretty routine engineering.

...and an all new
upper stage which uses an engine that while based on the venerable J-2 used
on the Saturns, was never fully developed. In other words, we have zero
flight experience with the upper stage and its engine.

Yes, *that* is a bit less routine, especially when the engine stopped
being the pretty-fully-developed J-2S and became the mysterious J-2X.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

wrote in message
ups.com...


Hmmm, Henry? I asked about such failure modes a while back. You
responded (Thank you), but the inclusion here of the reference to
segmented SRBs now leads me to wonder if your response actually covered
the issue I had in mind. Would a one piece Shuttle type SRB be far less
apt to have such catastrophic failure as, for example, the infamous
Titian event? Are there other catastrophic failure modes even for a
single segment?


Well, for one it's hard to say given no-one has flown one that large.

One issue is how do you make sure your pour is good? What if you end up
with voids or similar issus? It's much harder to detect and could be
equally catastrophic. (For example, if you create a major thrust imbalance
you could rip the ET in half.)


One reason I ask is I recall AeroJet, after the Challenger disaster and
a call for an advanced SRB, proposed a single pour design to do away
with the rubber gaskets that failed. IIRC, they actually wanted to dig
out pits at KSC and pour right there. They'd pour, let cure, do void
detection in situ, and extract the resulting SRBs.

It does seem, all in all, that solid rockets don't involve all that
much more danger. Especially if the segments are properly tested and
aren't stored for excessive periods before use.

Henry Spencer wrote:
In article ,
Jeff Findley wrote:
...NASA may continue to use external insulation on the ET for
various reasons, but protecting the booster from falling ice likely won't be
one of the primary reasons.

Correct. They'll still need to insulate at least the LH2 tank, to keep
boiloff rates within reason and to avoid the hazards of liquid air
dripping off the tank. And my guess would be that they'll continue
insulating the LOX tank just to avoid making unnecessary changes. But
damage to things below is unlikely to be a consideration.

How good an insulator is condensed ice? If it traps air bubbles, it
might do the job, especially if the tank is filled just before launch.
If all the ice breaks off on launch, this could be a weight efficient
form of insulation.

In fact, (thinking out of the box) with reference to previous
discussions about shedable insulation, might "spray on" snow be
possible?

In article . com,
Alex Terrell wrote:
Correct. They'll still need to insulate at least the LH2 tank, to keep
boiloff rates within reason and to avoid the hazards of liquid air...

How good an insulator is condensed ice?

On LOX tanks, actually pretty good. Unfortunately, on LH2 tanks, unless
conditions are just right, the liquid air running off sweeps the water
frost off, and you don't get a frost layer forming.

If all the ice breaks off on launch, this could be a weight efficient
form of insulation.

There's reason to think that not all of it leaves, alas. On the Saturn V
in particular, the weight of ice carried up to significant altitudes was
noticeable. (Mind you, the Saturn V was so huge that all sorts of
otherwise-ridiculously-small issues became noticeable.)
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