Worry over SRBs

I am most concerned with the SRBs. If one of these fails not only is
the Shuttle
finished so is Ares 1. I believe that one should be able to shut down
a booster
if problems are detected. This happened in one of the Gemini missions.
Also,
failures in solids develop too quickly. IMHO solids are fine for cargo
launchers
but crew should launch on liquids only.

wrote:
I am most concerned with the SRBs. If one of these fails not only is
the Shuttle
finished so is Ares 1. I believe that one should be able to shut down
a booster
if problems are detected. This happened in one of the Gemini missions.
Also,
failures in solids develop too quickly. IMHO solids are fine for cargo
launchers
but crew should launch on liquids only.

This reasoning is somewhat debatable. While it is true that liquid
fueled engines can be shut down in flight, would you really *want* to
shut one down, especially during the early portion of ascent? Losing
multiple liquid engines during the first few of minutes of flight
(which is when the SRB-derrived booster on Ares would be firing) almost
certainly would result in a Loss of Vehicle (in case of the STS), or an
launch tower abort situation (in the case of Ares).

Also, a solid rocket booster had considerably fewer moving parts than a
liquid booster, meaning there is less that can go wrong while the
booster is firing. Perhaps the most glaring shortcoming of the SRBs
that have been used on the shuttle are their segmented design. Since
the boosters are manufactured and refurbished in Promontory, Utah, they
have to be shipped to Florida in segments by railcar. Had politics
dictated that the SRBs be manufactured near KSC when the shuttle was
first designed, we might have ended up with a single segment design
instead, which would've completely eliminated the root design flaw with
the O-rings that led to the Challenger disaster.

I suspect on Ares that one of the abort scenarios will be for sensorsto
detect a sudden drop in chamber pressure in the SRB. If such a
situation is detected, then the Crew Escape System will be activated,
removing the CEV from the Ares stack and returning the astronauts and
CSV to Earth. The only other major ascent emergency that has to be
dealt with is loss of cabin pressure, which I suspect will be mitigated
by a return to full pressure suits during launch.

"Craig Cocca" wrote in message
ups.com...
This reasoning is somewhat debatable. While it is true that liquid
fueled engines can be shut down in flight, would you really *want* to
shut one down, especially during the early portion of ascent? Losing
multiple liquid engines during the first few of minutes of flight
(which is when the SRB-derrived booster on Ares would be firing) almost
certainly would result in a Loss of Vehicle (in case of the STS), or an
launch tower abort situation (in the case of Ares).

Shutting down the engine short-circuits a failure path which could lead to
an unsurvivable explosion or rapid structural failure. The idea is to
"soften" the environment the spacecraft must escape from. It also pads the
time an abort system has to react before things become real ugly.

Also, a solid rocket booster had considerably fewer moving parts than a
liquid booster, meaning there is less that can go wrong while the
booster is firing.

Simplicity doesn't always equate to reliability. Manufacturers must adhere
to an extremely tough quality assurance regimen to ensure successful
operation - and they don't always stay as strict as they should.

The problem with SRMs is that when things go wrong, they tend to get worse
very fast. A study of solid motor failures done by NASA revealed that the
majority of SRM failures have a sudden onset and extremely rapid propogation
of the failure. That calls into question the ability of an abort system to
react quickly enough to get the crew a safe distance away from the
explosion. Estimates are that an abort system requires approximately two
seconds to identify a failure, process its criticality, send commands for an
abort to execute, and then wait for those systems to operate and separate
the spacecraft to a survivable point outside the booster's blast field.

Perhaps the most glaring shortcoming of the SRBs
that have been used on the shuttle are their segmented design. Since
the boosters are manufactured and refurbished in Promontory, Utah, they
have to be shipped to Florida in segments by railcar. Had politics
dictated that the SRBs be manufactured near KSC when the shuttle was
first designed, we might have ended up with a single segment design
instead, which would've completely eliminated the root design flaw with
the O-rings that led to the Challenger disaster.

Single segments have their own set of problems, particularly when they are
the size of the monolithic boosters STS would've required. Attaining a
uniform insulation coating, propellant pour and inspection along the entire
casing would be very challenging. Cost would quickly become a factor. Ground
handling for such a behemoth would be a complete PITA. Monolithic SRMs as
are used on Atlas V, Delta II & IV are tough enough as it is.

I suspect on Ares that one of the abort scenarios will be for sensorsto
detect a sudden drop in chamber pressure in the SRB.

What about -51L's failure mode? There was no sudden drop in chamber
pressure - it was very small and gradual. A failure like that could fairly
quickly overwhelm the autopilot's ability to control the trajectory, leading
to strucutral failure somewhere in the interstage/second stage/spacecraft
areas.

If such a
situation is detected, then the Crew Escape System will be activated,
removing the CEV from the Ares stack and returning the astronauts and
CSV to Earth. The only other major ascent emergency that has to be
dealt with is loss of cabin pressure, which I suspect will be mitigated
by a return to full pressure suits during launch.

There are lots of major failure modes during ascent involving a multitude of
things, from structural failure to exploding batteries. Cabin pressure loss
is a serious, mission-ending failure, but it doesn't put the crew in
immediate peril the way many other ascent failure modes do. Launch vehicle
system failures tend to be far worse than spacecraft system failures during
ascent.

And, yes, the crews will be wearing full pressure launch & entry suits.
Preliminary work on their design has already started.

Kim Keller wrote:
Many, many interesting things snip : )

Kim, thank for the great reply to my earlier message. I hadn't
thought of many of the issues that you brought up, such as the
difficulting in fabricating/refurbishing large SRMs, or "softening the
failure environment" by shutting down a liquid fueled engine before
crew escape.

Couple of questions:

1) Are there any examples of an expendable rocket shutting its engines
down when a failure mode is detected, or do non-human-rated vehicles
only "fly or explode"? The only recent example I could think of where
the launcher shut itself down when something had gone wrong is on the
maiden launch of Space X's Falcon 1.

2) With regard to 51-L: Didn't it turn out that there was enough of a
chamber pressure differential between the left and right SRB where a
problem could have been detected had that system been monitored in real
time during launch (as I recall, the chamber pressures were being
recorded, but not monitored in real time)?

3) (Last question, I promise) You had mentioned that a NASA study
showed that problems in an SRM propagate more quickly than those in a
liquid-fueled booster. But couldn't it be reasonably said that the
relative simplicity of SRM design (as opposed to all of the plumbing,
turbomachinery, etc, of a liquid) makes it less likely that you'll ever
get into one of the rapid failure modes that you mentioned? Sure a
liquid fueled engine can "soft fail" to facilitate crew escape, but is
there any study out there that compares the failure rates of liquids
and solids, and shows one or the other to be less likely to fail?

On Sat, 08 Jul 2006 15:32:44 -0700, Craig Cocca wrote:



2) With regard to 51-L: Didn't it turn out that there was enough of a
chamber pressure differential between the left and right SRB where a
problem could have been detected had that system been monitored in real
time during launch (as I recall, the chamber pressures were being
recorded, but not monitored in real time)?

Yes, but a better parameter to look at would have been the gimbal angles
of the SSMEs and SRBs. When compared to the expected gimbal angles, it was
really evident that something was wrong. And, this occurred earlier and
was a larger change than the chamber pressures.

On Columbia, the same could be said about the "gimbel" or deflections of
the aerosurfaces. They too, when compared to the expected deflection
diverged radically.

If the controls are diverging radically from what is expected, something
is seriously wrong.

--
Craig Fink
Courtesy E-Mail Welcome @

On Sat, 08 Jul 2006 15:32:44 -0700, Craig Cocca wrote:



3) (Last question, I promise) You had mentioned that a NASA study
showed that problems in an SRM propagate more quickly than those in a
liquid-fueled booster. But couldn't it be reasonably said that the
relative simplicity of SRM design (as opposed to all of the plumbing,
turbomachinery, etc, of a liquid) makes it less likely that you'll ever
get into one of the rapid failure modes that you mentioned? Sure a
liquid fueled engine can "soft fail" to facilitate crew escape, but is
there any study out there that compares the failure rates of liquids and
solids, and shows one or the other to be less likely to fail?

Study?, wrt Challenger the failure propagate much slower than most
problems with liquid engines. The crew would had almost 10 seconds to
contemplate escape. Even after the vehicle came apart, they could have
escaped death. But, when a solid decides to turn itself into a
firecracker, I'd imagine that occurs rather quickly and there isn't much
comtemplation.

Hopefully, it's not the last question.

--
Craig Fink
Courtesy E-Mail Welcome @

wrote:
I am most concerned with the SRBs. If one of these fails not only is
the Shuttle
finished so is Ares 1. I believe that one should be able to shut down
a booster
if problems are detected. This happened in one of the Gemini missions.
Also,
failures in solids develop too quickly. IMHO solids are fine for cargo
launchers
but crew should launch on liquids only.


On Ares I, the primary difference between the shutte and the CEV will
be that the CEV will have a built-in launch escape system (LES) that
will be able to lift the capsule clear of the RSRM-derived first stage.
However, if you are thinking about what happened on Challenger, just
remember that in the unlikely event another leak in the joint were to
occur, it would not have the catastrophic effect (at least not right
away) that destroyed the Challenger ET and exposed the orbiter to
higher-than-designed-for aerodynamic stress.

Also, look back through the history of manned spaceflight, the
liquid-fueled rockets, like Soyuz can and have failed rather
spectacularly. In the case of Soyuz T-10-1, for instance, the rocket
caught fire, exploding only seconds after the Soyuz capsule's LES
lifted it from the doomed booster. If the launch control team had been
just a little bit slower firing the LES, cosmonauts Gennadi Strekalov
and Vladimir Titov would have been killed.
-Mike

Craig Fink wrote:

But, when a solid decides to turn itself into a
firecracker, I'd imagine that occurs rather quickly and there isn't much
comtemplation.

An important figure is the stored energy of the system.
In a solid rocket, there is (particularly near the end
of the burn) a large volume filled with high pressure
gas. The thrust chamber of a liquid rocket is much
smaller, and stores much less energy. I imagine the
turbines/pumps also don't store all that much kinetic
energy -- they're not very large.

Liquid propellant tanks are pressurized, so in a
pressure-fed system there's also a lot of stored
energy there. But the pressure in the tanks of
a pump-fed system is significantly lower.

Paul

"Craig Cocca" wrote in message
oups.com...

Kim Keller wrote:
Many, many interesting things snip : )

Kim, thank for the great reply to my earlier message. I hadn't
thought of many of the issues that you brought up, such as the
difficulting in fabricating/refurbishing large SRMs, or "softening the
failure environment" by shutting down a liquid fueled engine before
crew escape.

Couple of questions:

1) Are there any examples of an expendable rocket shutting its engines
down when a failure mode is detected, or do non-human-rated vehicles
only "fly or explode"? The only recent example I could think of where
the launcher shut itself down when something had gone wrong is on the
maiden launch of Space X's Falcon 1.

Engine shutdown is a range safety option the expendable rocket builder can
use instead of destruct charges. AFAIK, only SpaceX has gone that direction.
I don't know why other builders haven't chosen it.

2) With regard to 51-L: Didn't it turn out that there was enough of a
chamber pressure differential between the left and right SRB where a
problem could have been detected had that system been monitored in real
time during launch (as I recall, the chamber pressures were being
recorded, but not monitored in real time)?

Others here probably have better recollections of that discussion than me. I
only recall that the delta in Pc was very small at first and took a fair
amount of time to grow.

3) (Last question, I promise) You had mentioned that a NASA study
showed that problems in an SRM propagate more quickly than those in a
liquid-fueled booster. But couldn't it be reasonably said that the
relative simplicity of SRM design (as opposed to all of the plumbing,
turbomachinery, etc, of a liquid) makes it less likely that you'll ever
get into one of the rapid failure modes that you mentioned? Sure a
liquid fueled engine can "soft fail" to facilitate crew escape, but is
there any study out there that compares the failure rates of liquids
and solids, and shows one or the other to be less likely to fail?

I only know of the one study (never publicly released) by NASA, and none by
anyone else, but that doesn't mean there isn't one out there lurking in a
library somewhere.

It's probably fair to say that SRMs *should* be more reliable - with the
important caveat that the design is well understood and
manufacturing/handling/inspection processes are followed meticulously.

Kim Keller wrote:

Engine shutdown is a range safety option the expendable rocket builder can
use instead of destruct charges. AFAIK, only SpaceX has gone that direction.
I don't know why other builders haven't chosen it.

Most (if not all) the Russian boosters do it that way. However, it does
increase the chance of a more or less complete booster falling
somewhere down range and only going "boom" when it hits. Except for
very early in the launch (where it will be a big mess no matter what)
breaking the booster up before it hits almost certainly reduces the
chance of serious damage on the ground.

Several people commented after the Falcon 1 failure that SpaceX would
probably be required to install a destruct system before launching from
VAFB. I have no idea if that is actually the case.