I understood one of the big challenges in space was not cooking (due to all
the heat generated by your crew, your equipment, your weapons, your drives,
etc.) combined with your inability to radiate it effectively (I believe this
has something to do with space being a vaccuum and this being a fair
insulator?). Now, IIRC, the shuttle deals with this woe by jettisoning
material into which it has jammed a bunch of heat it wants to say goodbye to
(but I could be mistaken).
I've also heard about heaters now that use
directed heat - they heat what they point at -
essentially an IR radiator or something of the sort. Now, these are
electrically powered.
But is it conceivable that the waste heat from the ship could be usefully
transformed into emittable radiation (and directionally controllable at that)?
Or would this process never be efficient enough to meet the major need? I ask,
because if this was the case, having movable wings that could radiate heat
would be a good thing.... you could then radiate your heat *away* from a
direction you wanted to be stealthy in (assuming you knew which direction that
was!).
I find the whole space is cold, space is hot thing
interesting. In some sci-fi, you see it depicted
as amazingly cold, in others, things boil. The truth is, if I've got it right,
space (a vaccuum) is temperatureless (no matter to have a temperature). The
heat is the heat you bring with you or generate, and the cold is the result of
things like your O2 being allowed to vent into a zero pressure.... thus
sucking in heat to expand (endothermic?). Kind of a neat combination of
problems, really.
Tomb
Hi,
The interesting part is that there are several independent physical phenomena
that we call heat. In space, there is essentially zero convective or
conductive transfer of heat since in vacuo there is nothing to mediate these
processes.
However, near stars, the amount of radiant heat can be enormous. That is why
spacecraft are either white or silvered. These coatings reflect some of the
radiant energy, especially near the most intense frequencies emitted from the
Sun.
In the vast interstellar void, the temperature of space approaches the
background level, which is very cold indeed.
Cheers, Tony Christney
> On Sunday, March 16, 2003, at 11:36 PM, Thomas Barclay wrote:
> However, near stars, the amount of radiant heat can be
You mean I should have left my fleet alone after the white primer was applied
:)
Ok so all this is space hot or cold issue. Can someone put in simple terms
reactions
to using heat based weapons in space. Sci-fi literature talks of
lasers/blasters/plasma etc.
The tests that were run on lasers taking down missiles, I'm assuming that was
because of the heat of the laser rather than impact force?
Jeremey
> On Mon, Mar 17, 2003, Thomas Barclay wrote:
> I've also heard about heaters now that use
The largest problem with this would be efficiency. In order to radiate waste
heat from an entire ship, the radiators have to be very hot. Much hotter than
the ship itself (to sync the rest of the ship close to background (~3K), let's
say ~100K, would require the skin to be cooled 200K colder than the interior
(which is designed for habitability, and thus fairly close to 300K (~27
Centigrade)), and considerably colder than any likely power source). In order
to move heat to these radiators (which are hotter than the ship), requires
energy for active transport (2nd law
of thermodynamics -- heat will move from hotter to colder, unless you
push it the other way, and that takes energy). This energy *can't* come
from the heat itself (1st/2nd laws combined -- you get energy by moving
heat from hot to cold, not the other way around). To get this additional
energy to move the heat to the radiators, you need more power. Thus your
reactor generates additional power, and additional waste heat. So you have to
move *more* heat to the radiators. So the radiators are even hotter than the
rest of the ship. Thus, it takes more energy to move *any* of the heat over a
higher differential. Thus, you need more power. Which generates more waste
heat. Which has to be moved to the radiators.... This, of course, assumes that
your radiators will never melt. It also assumes that the energy used to
transport the heat is itself used with 100% efficiency (difficult when you
have such a high heat differential). It also assumes that you have an
extremely efficient way to *move* heat to such a hot surface, whether or not
you have the energy available (Thermodynamics will tell you how much energy it
takes to move heat from
cold->hot under ideal conditions. It won't tell you how to actually *do*
that). All of this ignores the problem of parts of the radiator vaporizing
(and thus emitting high-temperature gasses which might be as detectable
as the ship itself), and assorted other difficulties which would undoubtedly
be encountered in moving from Physics to Engineering.
Is it possible? Potentially. Is it practical? Unlikely. Is it economically
feasible? Almost certainly not.
-Brian Quirt
> Thomas Barclay wrote:
The shuttle deals with the overheating issue by leaving open the cargo bay
doors while in orbit.
> I find the whole space is cold, space is hot thing
Most often in sci-fi the whole "boiling" thing
is their attempt to show decompression (at least
in the sci-fi shows I've seen).
> The
Cold is just the absence of heat. When the astronauts are in orbit (okay,
anything in Earth orbit) they suffer extreme
temperature changes as they transition from day/night night/day.
When they are in sunlight, they heat up quite quickly. When on the night side
of Earth, they cool off quite rapidly. Satellites in orbit go through this
thermal transition and suffer from it as well. It is very stressful on the
satellites (example: the
Hubble's old solar panels would flex from thermal expansion/
contractions twice in its every 96 minute orbit, and because
of this thermal heating/cooling, the solar panels would "flap"
upwards of 8 feet at the ends, which would cause the spacecraft to suffer
pointing control problems, forcing the gyros to work overtime in order to keep
the spacecraft pointed at the desired target; the Hubble itself still suffers
from the whole thermal
expansion/contraction thing, but it is nowhere near as bad now
that we have the new, shorter solar panels).
Mk
> The heat is the heat you bring