covered by RCC reinforced carbon carbon (RCC) material just like your
experiment. The silica tiles are actually designed to keep the
aluminum skin of the shuttle from reaching 350 degrees F where the
alumminum looses strength. The tiles are very good insolators - they
delay the transmission of heat but cannot stop it. The tiles heat up
over time. Your experiement only applied the heat for a few seconds
at a time over a limited area and in a highly conductive media (the
air). For the shuttle ground to orbit is 8 and a half minutes.
Reentry (at least the hot part) is only about 16 minutes. Once the
shuttle reaches dense cool air the heat is drawn off of the tiles
away from the shuttle. The shuttle spends its entire mission bobarded
by 300ºC solar radiation across the entire exposed surface (roughly
half the shuttle at a time). The white tiles reflect most of it
away - the black tiles still reflect a lot of the heat but absorb
more than the white tiles. The shuttle uses the orbit path and
manuevers to allow the "hot" tiles to reradiate the accumulated heat
back into space (on the "dark" side of the orbiter.) They usually
include these maneuvers as part of the normal "corrective" burns.
I think people underestimate the complexity of the shuttle. Every
tile has a temperature sensor under it - they can detect missing or
damaged tiles by noting the sensor reading as they "roll" the shuttle
into the sunlight. A sensor that jumps way up indicates a missing
tile, while a sensor that is just a degree (or a tenth) different
than ajacent sensor might indicate damage.
The shuttle actually contains many heater units as well as cooling
units. Each of the engins must have a heater to maintain safe
operating temperatures (55 F to 200 F) for various elements of the
engine. The fuel and oxygen must be kept at specific temperatures.
The shuttle really has more concern about getting rid of the heat
generated by the flight systems electronics and the crew. The
shuttle bay doors have huge radiators in them that bleed the heat off
into space. Apollo 13 had power issues so the crew turned everthing
off except communications and life support. In Apollo 13's case all
the heat would have bleed into space eventually. The rate would
mostly depend on the quality of the inslulation. The interior would
have reached the -200°C range but the crew would have frozen long
before then. (They would have also run out of air before they froze.)
Spacesuits also have built-in heaters and coolers too. They are
really minature spaceship especially when attached to a maneuvering
unit.
> the "perfect" insulator : vaccum only blocks the conductive and
covective heat - it does nothing to block radiated heat. All matter
above absolute zero (-456.7ºF) radiate heat to some degree. How much
heat an object radiates is determined by it's temperature
differential with surrounding environment and the object's emissivity
factor.
All space habitats must include heat management systems as part of
the design. It has been shown that it is far easier and safer to use
solar-electric panels to generate electricity and then use electric
heaters where necessary. (Rember that raw sunlight has lots of
really harmfull stuff in it besides the heat and light.)
--- In , Tim whataname
wrote:
>
> Interesting points Tom, makes sense for the most part however,
regarding the shuttle tiles, they don't transmit heat very well,
sorta like the carbon-carbon material demonstration my dad used to
do in chemistry classes... for his demo he'd take a sheet of
carbonized cloth (IIRC) and would hold it in one hand and swipe it
a time or two with a blowtorch. Because, of the way they make the
stuff it wouldn't burn, least not at those temps. Same thing with
the shuttle tiles, they are physically quite weak, you can poke
holes in them with your finger, they're made of glass fiber with lot
of air pockets in them. They serve only to protect the shuttle
from the heat of re-entry. cite: documentary on Discovery channel
about the shuttle, the last one crashed and what was done to fix the
problem.
>
> The electronics and body heat likely go along way to keeping the
shuttle warm enough. Although this does bring up an interesting
subject... space is a vaccumm, the "perfect" insulator...the movie
on the Apollo 13 mission indicate that after they'd turned off most
of their electronic equipment that it got fairly cold in there. My
question would be how cold? Did they require heaters prior to the
accident or was the heat from all the electronic equipment enough?
How does that relate to Mir, Space Lab, and the ISS?
>
> Regards,
> Tim
>
> Tom
,
> >
> > Water - a good shield for Radiation?
> >
> Water is not really a good "portable" rad shield material. The
> shielding really has to have enough atoms to block the radiation
> particles/waves in order to work. A swimming pool reactor (which
is
> not use for electrical generation) uses a pool of water 20-30
feet
> in diameter 8-12 feet deep. The reactor pile is at the bottom.
> That is a really thick amount of material to put in a spaceship.
> RAD shielding can be made thinner by using high-density materials
> such as lead or gold. A solid shield needs similar mass as the
> water but takes up far less volume. When we get to TL 10+ and
start
> using crystaliron or superdense materials, the shielding gets
even
> thinner.
> >
> > Could we have double-hulls on spaceships and circulate water
> > around 'tween the hulls? If we're near a star, it could act
> > as a solar water heater.
> >
> Yes - although it would be tanks and plumbing rather than just
open
> space between the inner and outer shell. In direct solar
radiation
> (AKA Sunlight) the whole ship will heat up. It is more likely
that
> the water would be used to cool the sun exposed side of the ship
and
> to distribute the heat evenly throughout the ship. The sun side
will
> + 300ºC and the shade side will be -267ºC. A heat distribution
> system should be included as a standard part of the life support
> systems. (The US space shuttle uses orientation for some amount
of
> heat control - face the black tiles into the sun and the shuttle
> heats up - face the white tiles into the sun and the shuttle
cools
> down. (Those NASA guys are clever that way.)
> >
> > Could we build some sort of temperature diff. engine by taking
> > the warm water and the cold water?
> >
> These kind of thermal exchange systems are really not efficient
> enough to run a ship. But in an emergency it might run your life-
> support systems.
> >
> > Could future astronauts be equipped with gills and the ship be
> flooded?
> >
> T20 added Dolphins as an uplifted race. They also added an
aquatic
> race. Neither of these races use liquid filled ships. Water and
> Electrical circuts just do not mix very well.
> >
> > -Joel
> >
>
>
>
>
>
>
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