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Grex > Agora47 > #35: NASA management screwed up BIG time. Now what? | |
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| 22 new of 71 responses total. |
mdw
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response 50 of 71:
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Oct 5 06:41 UTC 2003 |
In order for the shuttle to "move a short distance, roll, and come back"
it has to fire maneuvering thrusters, scattered in random locations
across the shuttle. I wouldn't care to be in an EVA suit hit by the jet
of one of those things -- the jet itself *might* be harmless, but it's
probably going to impart significant random delta V and angular
momentum, and without an MMU (or SAFER), that's probably going to be
fatal. This is a good example of the reason they reherse and plan these
things out on the ground before trying them out in space. Without
gravity and a convenient flat surface, *everything* is much harder.
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aruba
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response 51 of 71:
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Oct 5 14:11 UTC 2003 |
But harder doesn't mean impossible, and it certainly doesn't mean "not worth
doing".
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murph
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response 52 of 71:
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Oct 5 14:47 UTC 2003 |
I think that, in the case of putting an astronaut in space and maneuvering
the shuttle around him, "harder" means "basically impossible". The space
shuttle is not a graceful beast; trying to move it around like that would be
a laughable proposition.
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gelinas
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response 53 of 71:
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Oct 5 15:29 UTC 2003 |
(There is work being done with plasma containment, but it seems to be aimed
more at fusion power than heat shielding. Still, things seem to spin off of
basic research. ;)
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scott
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response 54 of 71:
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Oct 5 17:23 UTC 2003 |
It might be feasible to have the shuttle and a camera satellite coincide, and
have the shuttle do a slow roll wile being photographed. Being out of the
atmosphere should help with getting a good image.
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rcurl
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response 55 of 71:
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Oct 5 19:05 UTC 2003 |
The shuttle is "graceful" enough orient and dock with the space station.
No more maneuverability than that would be necessary for an inspection.
The camera satellite can, as I've mentioned, be released from the
shuttle itself.
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russ
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response 56 of 71:
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Oct 5 19:13 UTC 2003 |
Re #49: The high-Tc superconductors I'm talking about are the
ones which run at temperatures around 80 K, not 3000 K. The
Shuttle carries liquid oxygen (BP around 83 K) for the fuel
cells, so chilling a superconductor loop to that temperature
shouldn't require any consumables that aren't already carried.
The liquid hydrogen is another possibility, but I'm not sure
how much heat it would sop up in the boiling process; the
delta-H-fg is pretty small as the entropy increase is about
the same as for other diatomic gases but the absolute
temperature is much closer to zero.
If we could find a way to hold the hot gases at a distance
that seriously limits the heat transfer to the vehicle,
something like the Shuttle could use titanium leading-edge
skins instead of brittle carbon-carbon. The other virtue
of a magnetic system is that you can test it before hitting
the atmosphere and be sure it's working.
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rcurl
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response 57 of 71:
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Oct 5 19:37 UTC 2003 |
That can be done with transpiration cooling. This is done by using a
porous surface and forcing a gas out through the surface, and uses
comparatively very little gas compared to that which would be required to
just cool the surface. The transpiratioin moves the hot boundary layer
further from the surface. It has been used to protect gas turbine blades
from heat. I would think, though, this would be mechanically complicated
for the shuttle and of course would add extra weight for the piping and
gas storage and control. The tile system was probably driven mainly by
weight concerns.
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gull
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response 58 of 71:
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Oct 5 20:57 UTC 2003 |
I recall years ago they experimented with a system for reducing the drag
of aircraft wings that involved injecting compressed air into the
airstream through small holes along the wing surface. The system worked
great, but the problem of keeping the holes clean turned out to make it
totally impractical. A transpiration cooling system might have similar
problems.
Maybe our primary mistake was going to a reusable spacecraft to begin
with. I've heard it said that each shuttle launch costs *more* than a
Saturn V launch would, so it seems like a reusable spacecraft has been a
poor tradeoff. You have a lot more heat shield options if you don't
need to reuse the shield for another launch.
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other
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response 59 of 71:
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Oct 6 01:30 UTC 2003 |
May if the vehicle was reusable but the heat shield was one-time?
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bru
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response 60 of 71:
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Oct 6 02:08 UTC 2003 |
I was thionking something similar. What were the heat shields of previous
craft made of? Weren't they a spray on paint like material? Could something
like this be applied after every use of the shuttle?
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gelinas
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response 61 of 71:
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Oct 6 02:21 UTC 2003 |
"Materials: Capsule hull is titanium coated in fiberglass insulation,
covered with shingles of nickel-steel alloy. The rounded heat shield on
the base is made of fiberglass and a strong plastic called phenolic resin"
(http://www.casciencectr.org/Exhibits/AirAndSpace/HumansInSpace/Gemini11.ph
p).
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gull
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response 62 of 71:
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Oct 6 02:41 UTC 2003 |
I think some very early Soviet designs even used oak.
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russ
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response 63 of 71:
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Oct 6 03:11 UTC 2003 |
Re #58: You've got it backwards. The boundary-layer control
systems work by pulling the stagnant surface air in through
the holes; blowing air out causes the airflow to separate.
Re #57: Transpiration cooling requires a coolant; it's just
another form of ablator. NASA went from ablative heat shields
to refractories because the long, gradual descent of Shuttle
would have required way too much weight of ablator. The
heating rate of Shuttle is low, but the total heat load is high.
The advantage of a magnetic shield is that it does not
require expenditure of mass to renew the protective layer.
Now I'm wondering how hard it would be to perform a test on
a Shuttle external tank. You could put the superconducting
coils inside the oxygen and hydrogen tanks and energize them
with batteries after separation from the orbiter; you'd have
your test results a few minutes later when the tank hit
atmosphere over the Pacific.
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scott
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response 64 of 71:
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Oct 6 13:38 UTC 2003 |
Re 60: The big problem with trying to use the pre-Shuttle heat shield designs
is weight. The old space capsules were much smaller than the Shuttle, asd
so a heavier material was feasible. If they put that stuff on the whole
Shuttle it'd never get into space.
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gull
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response 65 of 71:
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Oct 6 15:54 UTC 2003 |
But you could also save a lot of weight in other areas if you weren't
planning on re-using the spacecraft.
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tpryan
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response 66 of 71:
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Oct 7 00:13 UTC 2003 |
'Unheard of' means not dreamed of yet,
'Impossible' means not yet done.
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russ
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response 67 of 71:
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Oct 8 02:18 UTC 2003 |
I saw an editorial the other day (by Jake Garn?) claiming that
we needed to put the Shuttle back into service ASAP and that
any alternatives were ten years off.
Funny, I don't think it would take more than a few months for
Scaled Composites to turn out a graphite-fiber version of the
Apollo command module. We could be flying in two years, I bet.
Given our advances with solid-state devices such as fiber-optic
gyroscopes, it should be very easy to build a vehicle that
could be flown to the station, left there for months to years,
and flown back safely. It would just come down under a 'chute
instead of with wings, and hit water instead of pavement. BFHD.
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gull
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response 68 of 71:
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Oct 8 14:27 UTC 2003 |
Of course, why design it ourselves when we can buy it off the shelf from
the Russians? ;>
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tod
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response 69 of 71:
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Oct 8 16:52 UTC 2003 |
This response has been erased.
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albaugh
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response 70 of 71:
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Oct 27 18:32 UTC 2003 |
http://www.unitedmedia.com/comics/peanuts/archive/peanuts-20031027.html
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willcome
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response 71 of 71:
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Nov 27 07:43 UTC 2003 |
He didn't write enough about whores.
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