Re: Ejection seat

From Jeff Findley:
"Stuf4" <tdadamemd-spamblock-@xxxxxxxxxx> wrote

The point made previously was that for both -51L and -107 the crew
compartment was observed to have separated cleanly from the debris
field, so I don't see much merit to an argument that designing a system
to deliberately do this would be difficult.

So, since we just saw a C-5 split apart not far behind the cockpit because
it couldn't make the runway during an emergency landing that it would also
be easy to design the nose of a C-5 to become an escape module and parachute
to earth?

I don't know about crew escape, but splitting apart certainly
facilitates unloading the cargo after you crash. And it would
certainly add to the embarrassment if the pilots were smuggling
something (as cargo crews have been known to do on occassion) and then
the palet gets cracked open for all the world to see.

Having part of an aircraft break apart in an accident doesn't mean it would
be easy to make that part an escape module. Just because the crew cabin of
Challenger was ripped off the body of the orbiter due to aerodynamic forces
(trailing debris, without power, and very likely without a completely air
pressure intact inner cabin) and a clean separation that insures you have
power, an intact pressure cabin, and is aerodynamically stable.

What you are witnessing is proof testing of loads and failure
mechanisms. The way a C-5 splits apart is proof of how it was loaded
and where it was structurally strong and where it was weak. The same
applies for Columbia and Challenger.

Now let's look at some key differences here:

- Fatality rate
I imagine that if one C-5 blew up every week with no survivors,
they would put a lot more focus on emergency egress of that bird. This
was the second C-5 write off since long before STS-1. And I notice
that the body count at Dover was Zero.

- Operating altitude
The C-5 spends a lot higher percentage of its flying time a lot
closer to the ground, so the drogue would probably just insure that
everyone would smash into the ground in a stable manner.

- Pressurized cabin
The entire fuselage of a C-5 is pressurized. There is no derived
benefit from starting with the pressure vessel as the basis of a crew
escape module. But you do get that benefit in a vehicle like the
F/FB-111, B-1A or the Space Shuttle.

As for the pressurization issue, that is another non-requirement.
Remember why Apollo, Gemini and Mercury astronauts wore full pressure
suits on ascent and entry.

....now think back to the reason why they *didn't* on the shuttle:

Because they went in knowing that they had no hope of survival in these
emergency egress situations!

Now had they been given an escape module, everyone would have worn
pressure suits just like every astronaut before them. If the module
sprung a leak during separation, they could all still survive just
fine.


And let's be clear about electrical needs...

The standard for egress systems is to design them so that they *do not*
require any electrical power from the vehicle in order for them to
function properly. That goes for capsules, clamshells, ejection seats,
parachutes, etc. They are designed with independent mechanical systems
and self-contained pyrotechnic charges and the like. Any internal
electrical needs get handled with batteries.

As for the SR/D-21, you might consider that a unique case seeing how
little separation there was from control surfaces. Now if the D-21
carried the crew, was shaped like a block and you write off the SR-
mothership as lost, then you might have a very survivable situation
that is comparable to a shuttle crew ejection module.

If your D-21 recontacts the M-21 (not SR-71, which is a sloppy mistake),
your D-21 is very likely just as destroyed as your M-21.

Same with the shuttle. If you eject the crew cabin and it recontacts the
wing, the wing could rip a hole in the crew cabin and/or could cause the
cabin to enter an unrecoverable spin.

I agree with the notion that there are many ways for a shuttle crew to
get killed after the ejection module sequence had been initiated. But
I don't see a hole being ripped into the cabin as necessarily fatal.


As for any supposed sloppy mistakes, you may have noticed that I never
used any designation "SR-71". And I expect that you know what the D-
and M- designations stood for when I spoke about the "mothership".

As to the notion of me underestimating heat shield design, the word I
got straight from Max Faget was that heat shields were way
overdesigned. He told me that Apollo could have gotten away with a
much thinner shield.

True, but that doesn't diminish the fact that you'd have to design the crew
cabin to eject and take the heat of reentry which is *different* than if it
were still attached to the orbiter flying a hypersonic lifting trajectory.
Note you're going to have particular trouble with the windows if you choose
a nose first attitude (like a Discovery capsule).

I'm not so quick to agree that the current window design is inadequate.
I would favor a nose-first attitude simply to minimize dynamics. But
the windows might work just fine because the weight of the cabin-module
by itself is so light compared to a whole orbiter which equates to a
vast reduction in energy that needs to be dissipated.

If you choose a base first attitude, then my guess is you'll have a lot of
trouble making it stable in that orientation. not to mention the fact that
you're going to have lots of wires, pipes, and at least one big hatch you
need to run through your heat shield. Not an easy task.

Whatever the design, there would certainly be a lot of details that
would need to be looked at.

But I am of the opinion that if you start with the premise that crew
survivability is a high priority, then you will find the answers that
will get you to that endpoint.

And I totally disagree with the view that a new vehicle needs to be
designed for the task of making a shuttle ejection module. A smart
design approach would be to simply take the already designed crew
cabin, alter it for aerodynamic stability (mainly by adding a drogue
chute) and alter it for thermal protection (mainly by adding tiles or
some other type of heat shield, and this doesn't add much weight).
Very simple.

How is your drogue going to survive reentry heating? How do you make the
windows heat resistant enough to survive? When this is all said and done,
what happens to the shuttle's center of gravity and payload capacity? How
do you propose to test this thing so that you're reasonably confident that
it will work for both a Challenger (max dynamic pressure) and Columbia (very
nearly max reentry heating) style disasters?

Consider the fact that STS-1 was the first full-up test of the orbiter.
Young and Crippen got to orbit and were looking out on all the missing
tiles wondering how they were going to survive the entry.

As for cg and payload impacts, I was suggesting a minimal effort design
that would have a very low impact on cost and weight. Now if you
wanted a zero-zero escape module, that's where things get prohibitive.
And I can understand how it got axed early in the design phase. When
you start adding on huge rocket motors, impact attenuation bags and the
like, you start driving your payload toward zero.

I expect that the hardest part was to design survivable impact loads
from when it hit the ground (while keeping weight under control). Here
the easiest answer is to have the crew jump out on the way down
(especially since they could have so much time to do this).

NASA has put many dollars into studying shuttle escape. The standard
answer is that it is too late to go back and redesign something that
would have been easy to do in the first place.

That's because it's the right answer, especially when you're talking about
the payload hit you'd take when flying to ISS. And this assumes that all
the other issues are workable.

I agree with the conclusion that it is not smart to retrofit the
shuttle with an escape module. The designs that NASA came out of that
study with were hideous.

The answer that I don't see anyone pressing NASA for is their reasoning
for eliminating the crew escape module in the first place. Both Gehman
and Rogers were negligent in not calling those people for testimony.
Details about o-rings and foam are all tertiary topics. There are
thousands of ways to destroy a shuttle. There was no way to save those
crews.

Robert Thompson is one person who would be on the short list. And the
ASAP panel that accepted his answer way back in 1973, prior to the
Orbiter PDR, that it would be too costly to do a redesign... those
people would make the short list as well.

Fletcher is the most obvious. Imagine his reaction when he was first
briefed... "What do you mean there is no provision for crew egress?!"
And then someone sold him on the idea. How tragically sad.

I'd rather not imagine what Fletcher thought. The past is gone. It would
be folly to say that *today* it would be "easy" to design an escape capsule
for the shuttle.

So you're probably not too interested to know how well Fletcher slept
at night after being *reinstated* as NASA administrator after
Challenger...

The goal I seek in holding decision makers accountable is to learn from
the past so that we can be smarter about the future. For all I know,
Fletcher had an excellent reason for signing off on a shuttle that had
no crew escape system. But we will never get the answers if we don't
ask the questions.


~ CT

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