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Sock Munkey
2005-Feb-24, 11:11 AM
A thought has occured to me regarding re-entry.

The atmosphere around a ship traveling at such hyper-velocities is highly ionized due to the heat and as such is highly electricly conuctive.
This being the case, is it theoretically possible to use a magnetic field to repel the superheated air from the skin of the ship?

crosscountry
2005-Feb-24, 01:31 PM
it is ionized, that's why we see streaks. sometimes we hear meteroids too. I definitly heard Columbia when it passed over my house 2 years ago. But that was sonic pressure not ionization.

in order to repel anything magnetically it must be magnetic right? thost ionized atmosphere molecules aren't moving (much relatively to the "meteor")

The real case however is that we need the "air braking" to slow our ships. if there were no ram pressure our ship would have too much velocity, and the parachutes wouldn't be able to stop it before it hit ground. we would be required to use fuel to decelerate, and that's way more expensive than a heat shield due to weight and cost.

DoktorGreg
2005-Feb-24, 02:24 PM
A couple of things...

The reason they WANT heat when re-entering the atmosphere is to convert speed to heat. The more heat the space craft can take, the less deltaV you need to de-orbit the craft.

On the use of electromagnets... I dont see a reason it wouldnt work, but the system (large heavy coils of copper wire) would be heavy. it might be easier to carry extra fuel and burn off the speed while still outside atmosphere. Carry enough fuel and you dont have any speed to burn off during re-entry at all. But then you need some sort of hypergolic fuel. yuck. or atmospheric nuclear rockets, even worse.


I think modern technology has an answer, but its not the sort of thing people like because it has a ... french... quality to it. Big inflatable wings. Make big inflatible wings out of some sort of mylar and kevlar composite fiber. Really big. Several hundred yards for a shuttle sized vehicle. Then just use a slower re-entry profile.

crosscountry
2005-Feb-24, 02:51 PM
and have a heat shield incase those wings torque off.

Sock Munkey
2005-Feb-25, 05:57 AM
Ionized gas has an electrical charge so yes it is affecte by magnetic fields, that's how experimental fusion reactors contain the plasma.

As for drag, the fact that the air has to be pushed aside means there will be drag. It's questionable how much the system would wiegh, but I don't imagine it would be significantly heavier than the skin of heat tiles currently used.

It would certainly be far less fragile. Those tiles break like glass.

Carrying more fuel for deceleration would mean having to carry it up in the first place increasing the wieght of the craft to an impractical level.

Anyhow, I envision my system being powered by a small turbine spun by the high-speed air stream as the craft decends. This eliminates the need to carry a power supply for it.

The bottom line for this is that it would protect the craft from the worst of the heat giving it a longer life and less maintenence.

So what do all of you serious rocket-heads think of my concept?

Evan
2005-Feb-25, 04:11 PM
It would need a very poweful power source. Read "large and heavy".

DoktorGreg
2005-Feb-25, 05:51 PM
Ionized gas has an electrical charge so yes it is affecte by magnetic fields, that's how experimental fusion reactors contain the plasma.

As for drag, the fact that the air has to be pushed aside means there will be drag. It's questionable how much the system would wiegh, but I don't imagine it would be significantly heavier than the skin of heat tiles currently used.

It would certainly be far less fragile. Those tiles break like glass.

Carrying more fuel for deceleration would mean having to carry it up in the first place increasing the wieght of the craft to an impractical level.

Anyhow, I envision my system being powered by a small turbine spun by the high-speed air stream as the craft decends. This eliminates the need to carry a power supply for it.

The bottom line for this is that it would protect the craft from the worst of the heat giving it a longer life and less maintenence.

So what do all of you serious rocket-heads think of my concept?

I have a question.... Have you ever seen an electromagnet? Googling around I found the density of the white shuttle tiles is ~9lbs per cubic foot. Sitting under my desk, I have a 400watt transformer. It is roughly six inches each side. It weighs about 30 lbs. Granted a transformer is not an electromagnet, it is a big coil of copper wire. Onto the power supply for your electromagnet. You need a big generator in addition to your turbine. Guess what that is? You got it, another big heavy coil of copper wire.

I know, maybe we can throw some superconductors in to reduce the weight. Ok now we need a cooling system to chill the brittle ceramic (notice the irony here) wires...

Ill give you this one, we can operate the heat pump with your turbine. But now we have all this extra heat to deal with, and since the outside of the space craft is a plasma heated environment, se we have to contain the heat somehow. I know where we can find exatly the material designed for this purpose! The heat tiles we removed to make room for the ceramic superconducting magnet!

Also, with a strong enough magnet the material we are trying to push away doesnt even need to be ionized. See the flying frog (http://www.hfml.ru.nl/froglev.html) demonstration

jnik
2005-Feb-27, 02:27 AM
The reason they WANT heat when re-entering the atmosphere is to convert speed to heat. The more heat the space craft can take, the less deltaV you need to de-orbit the craft.
The heat would still exist--it would just be further away from the spacecraft. There's actually a really good analogy here: the Earth in the solar wind.

Ignore the fact that the solar wind carries a magnetic field for now. It's flying towards the Earth at a few hundred km/s (alternatively, you can think of the Earth flying into the stream at a few hundred km/s...Galilean frame transform). Since it's practically 100% ionized, the solar wind can't cross the Earth's magnetic field (charged particles "can't cross field lines"--a simplification, but true enough for this). The particles "pile up" on the Earth's field and form a bow shock closer to the Sun. In passing through this shock the particles are slowed and heated, so that they're going slowly enough to pass around the magnetosphere.

You can figure how big a magnet is needed (and thus how much current, how much wire, etc.) by figuring that the magnetic pressure (B^2/2*mu-naught) balances the pressure of the atmosphere (atmospheric density*square of the spacecraft velocity). The point where that happens is the closest plasma will come to the spacecraft.

Unfortunately, I think incomplete ionization would also present a problem, on top of the massive magnet requirements. Interesting idea though.

eburacum45
2005-Feb-27, 06:39 AM
This is where a supply of monopoles would really be useful.

publiusr
2005-Mar-02, 06:46 PM
You can beam power to a painted sail, as Benford suggested, keeping your "fuel and engines" at home.

But you need HLLVs to put that up there.

There is no way around it. For space exploration to grow--you need heavy-lift.