Superconductor magnet spacecraft heat shield being developed

Dear YKhan:

On Nov 27, 3:52*pm, YKhan wrote:
On Nov 27, 2:15*pm, dlzc wrote:

The very thought of this makes my eyes want to
cross. *You don't get the plasma unless your craft
is interacting with the atmosphere, so if you divert
the plasma away, you no longer make a plasma,
you don't get braking, etc.

What sense does this make?

Well, I doubt they're talking about total diversion of
the plasma away from the spacecraft. Perhaps
they're talking about just enough diversion to require
lighter heat absorbent materials than what are on
the Space Shuttle?

Same problem. If they move "some of" the plasma away, then they are
reducing net friction.

The plasma forms because the gas has to have its temperature increased
high enough that the speed of sound in that material will allow it to
get out of the way of the spacecraft. This removes energy from the
spacecraft.

David A. Smith

Yousuf Khan wrote:

eric gisse wrote:
I love the concept, I just don't see how such a thing is practical
though. Unless my estimates of the required energies are wayyyy off.

I doubt they're talking about a magnetic field so strong that it can
deflect all of the particles of atmosphere from even touching the skin
of the vehicle. They're probably just talking about a magnetic field
strong enough to deflect a certain percentage of the plasma particles
away, to lower the temperature on the skin, let's say reduce the
temperature from 2000° to 1000° or something like that. This way they
may still need some kind of heat-resistant material on the skin, but
they can find something lighter and less brittle than Space Shuttle tiles.

Yousuf Khan

The Lorentz force is proportional to field strength, but energy density of
the field goes as the square of field strength. Not good, not even with
clever field geometries.

Given that the atmosphere only _becomes_ a plasma as a result of heating
from the bow shock as the craft pushes through the atmosphere, it would take
one HELL of a field to deflect even a miniscule portion of the plasma away
from the craft given the rather short length scales in play.

I'll put this in the box of ideas that only work with an absurdly powerful
energy source.

Nothing wrong with exploring ideas but I don't see anything better than
ablative shielding on the horizon.

dlzc wrote:
On Nov 27, 3:52 pm, YKhan wrote:
On Nov 27, 2:15 pm, dlzc wrote:
Well, I doubt they're talking about total diversion of
the plasma away from the spacecraft. Perhaps
they're talking about just enough diversion to require
lighter heat absorbent materials than what are on
the Space Shuttle?

Same problem. If they move "some of" the plasma away, then they are
reducing net friction.

I understand what you mean, but there must be a temperature at which
normal gases of a any particular kind becomes plasma (i.e. gas with
dissociated electrons). Since you need that charge differentiation to
move anything with magnetics, if they move the plasma out of the way,
then it cools to a point where it is no longer plasma and no longer
magnetic, then starts hitting the spacecraft skin again and heating up
again. This may be happening over milliseconds, where it's going from
normal gas to plasma and back and forth. So they may be able to keep the
skin temperature very precisely at the plasmification point rather than
several hundred degrees above it. Just cool it down enough to require
less heat resistant materials -- thus achieving weight-savings, or
cost-savings, or both.

The plasma forms because the gas has to have its temperature increased
high enough that the speed of sound in that material will allow it to
get out of the way of the spacecraft. This removes energy from the
spacecraft.


I think that having a magnetic field diverting plasma will do the same
job of slowing the spacecraft down as much as if the plasma were hitting
the spacecraft skin.

Yousuf Khan

Dear Yousuf Khan:

On Nov 30, 10:50*am, Yousuf Khan wrote:
dlzcwrote:
On Nov 27, 3:52 pm, YKhan wrote:
On Nov 27, 2:15 wrote:
Well, I doubt they're talking about total diversion of
the plasma away from the spacecraft. Perhaps
they're talking about just enough diversion to require
lighter heat absorbent materials than what are on
the Space Shuttle?

Same problem. *If they move "some of" the plasma
away, then they are reducing net friction.

I understand what you mean, but there must be a
temperature at which normal gases of a any
particular kind becomes plasma (i.e. gas with
dissociated electrons). Since you need that charg
e differentiation to move anything with magnetics, if
they move the plasma out of the way, then it cools
to a point where it is no longer plasma and no longer
magnetic, then starts hitting the spacecraft skin
again and heating up again. This may be happening
over milliseconds,

Less.

where it's going from normal gas to plasma and
back and forth. So they may be able to keep the
skin temperature very precisely at the
plasmification point rather than several hundred
degrees above it.

To do that reduces net friction. You plow into the planet.

If you kill most of the momentum where the air is thin, then the
temperatures may be high, but it does not involve a lot of mass to
transfer heat from. The temperature inside a fluorescent tube is 6000
deg C, give or take, but the envelope temperature is ~40 deg C or so,
because the internal pressure is low.

Just cool it down enough to require less heat
resistant materials -- thus achieving weight-savings,
or cost-savings, or both.

The shuttle heat tiles, when attached, are already damned light. But
yes, they saved something like 5000 pounds of lift-off weight by not
painting the external tank. Of course, they also inherited partially
adhered frost-bergs to have to hope don't hit anything important on
the way up...

The plasma forms because the gas has to have
its temperature increased high enough that the
speed of sound in that material will allow it to
get out of the way of the spacecraft. *This
removes energy from the spacecraft.

I think that having a magnetic field diverting
plasma will do the same job of slowing the
spacecraft down as much as if the plasma were
hitting the spacecraft skin.

No, it won't. The magnetic field performs no real work. At least in
a motor, there is a frame where the magnetic field looks like a
rotating electric field, and work is obtained. All the magnetic field
will do is possibly increase the heating rate along the entire skin of
the craft, and require fuel to drive it.

They should experiment with injecting water or liquid waste into the
hot spot, and let a phase change absorb some of that heat. That at
least makes sense, even if it doesn't smell all that good. That way
the wetted surface stays close to the vaporization temperature of the
liquid... And yes, this would also probably add weight.

David A. Smith