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Let's talk about thermal protection systems

Posted by: 8900 - Sun Oct 30, 2005 9:32 am
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Let's talk about thermal protection systems 
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Post Let's talk about thermal protection systems   Posted on: Sun Oct 30, 2005 9:32 am
In nowadays, spaceship use carbon tyles to protect the spaceship during reentry. However, sometimes the tyles are damaged and cause great danger to astronauts.

I am wondering why people don't use a strong magnetic field to protect the spaceship(for example: space shuttle).
What makes this idea impractical?
anyone can answer me? thx. :D


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Post    Posted on: Sun Oct 30, 2005 10:31 am
As far as i know there's research at the university of Bremen, Germany regarding electrodynamic thermal shielding for hypersonic flight and reentry applications. I'll try to dig out a bit more of information.

edit: typo


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Post Re: Let's talk about thermal protection systems   Posted on: Sun Oct 30, 2005 8:15 pm
Welcome to the boards, 8900 and Herr Schmidt. We're glad to have you!

8900 wrote:
I am wondering why people don't use a strong magnetic field to protect the spaceship(for example: space shuttle).
What makes this idea impractical?


The operative word here is "strong". Unless I'm very much mistaken, the magnetic field required to push away an atmosphere as thick and as weakly charged as the Earth's would be absolutely insane. Thus, the magnets required, and the power source to drive them, would probably be more massive than the lift capability of any rocket imaginable.

For information on how one of our older members is applying electromagnetics to spaceflight, check out this topic. I've just sent a PM to timallard to look at this thread, so he should be replying here in a couple days.

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Post    Posted on: Sun Oct 30, 2005 8:24 pm
Uh spacecowboy.. I just looked behind me, if there stands my father.."Herr" Schmidt.. I'm not *that* old ;). Also I'm not that new to the forums but i didn't post much. Just call me Klaus, it's the Internet ;)


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Post    Posted on: Sun Oct 30, 2005 8:25 pm
I stand corrected; I was always made to understand that Herr simply meant "Mr." -- and I'm usually polite to people on the first occaison I meet them. From then on, I'm liable to be rude and annoying, but I'm nearly always polite at first.

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Post Energy source   Posted on: Sun Oct 30, 2005 8:58 pm
What about using nukes as an energy source?

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Post    Posted on: Mon Oct 31, 2005 12:49 am
In terms of physics, it's possible with basic EMF and tons of current load since the heating is creating ions and those can be acted upon by fields, but, that wouldn't be practical if it takes a lot of metal to carry that current.

My own research into this idea makes me feel that ultimately using this strategy will become practical as more is known about this type of system. I'd suggest a crucial factor is the shape of the vehicle when using any type of magneto-hydrodynamic or EMF system for re-entry, or, propulsion.

The incipent wave created by compression thickens and heats the farther into the atmoshpere the craft falls, but this is what's braking the vehicle so the only added function using MHD/EMF required is to move the action far enough away from the skin that it doesn't heat up as much.

I'd say we need more specific research into both how to thicken the boundary layer, and to free the skin from the stream of super-heated ions by perhaps breaking the bond between the air and skin as this would really reduce the heat transfer efficiency.

tom

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Post    Posted on: Mon Oct 31, 2005 8:54 am
o, i see.
so, one more thing for me to ask
the heat is generated due to the high entry velocity
Can the spaceship lower its speed (by any means) during reentry to reduce friction and prevent the rise of temperature to a very high level? thx.


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Post    Posted on: Mon Oct 31, 2005 8:59 am
8900 wrote:
o, i see.
so, one more thing for me to ask
the heat is generated due to the high entry velocity
Can the spaceship lower its speed (by any means) during reentry to reduce friction and prevent the rise of temperature to a very high level? thx.

Yes, a powered landing is possible.
The problem with powered landing is, that the fuel needed to achieve this powered landing needs to be brought first into space, adding a lot of extra weight at launch, requiring more energy for launch + the extra energy needed for powered landing.
And that's very expensive, but it is possible.

And of couse there're a few other ways to lower speed.. as parachutes.. but they can't be used on a very large altitude.. only on the last part of the road back home.

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Post    Posted on: Mon Oct 31, 2005 2:22 pm
Could the skin of the craft be made with lots of little holes from which air / gases are pumped so they lift the friction heated atmosphere away from the surface? Sort of like those air hockey games you get at the arcade. What sort of pressures are we talking about on reentry? Perhaps the air could be harvested from the cooler cone of atmosphere behind the decending craft?

I guess the problem's here are plenty, while simple glue on tiles or carbon carbon panels are cheaper and simpler to fix.

Would modifying the profile of the craft during descent to introduce a greater surface area be any help in more effective aerobraking? I'm thinking that the quicker the ship slows, the shorter tile heating time. Something like fighterjets swing wings, but for the opposite reason.

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Post    Posted on: Mon Oct 31, 2005 4:58 pm
The cooler air behind the craft would also be at a much lower pressure, so you would have to pump it rather than 'collect' it, which make things a lot more complicated. Any sort of collection system that took in ram air would also, of course, need to be cooled because it would suffer the same problems of frictional heating, so, perhaps not a feasible concept.

WRT greater surface area to reduce heating time - astronauts already pull a a lot of G in the shuttle - decelerate any faster and the G forces would be too great for manned spaceflight.


James


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Post    Posted on: Mon Oct 31, 2005 10:57 pm
Sean Girling wrote:
Could the skin of the craft be made with lots of little holes from which air / gases are pumped so they lift the friction heated atmosphere away from the surface? Sort of like those air hockey games you get at the arcade.


An “insulating spacer” of this type forms automatically when the reentry shield is BLUNT. The thickness of this insulating layer is proportional to the radius of curvature of the heat shield. (See NACA Report 1381 (Allen & Eggers) 1957) Sharp leading edges, like those required for good lifting wings, provide much less insulation. Mention is often made of temperatures of a few thousand degrees. The actual “Temperature” (corresponding to the energy density) of the plasma shock is about 40,000 C - much hotter than the surface of the sun – which is why it is a plasma! The equilibrium temperature of the heat shield surface, with the heat flux “leaking” through the insulating air layer balanced by radiation from the surface, runs from about 1000 C to 10,000 C depending on how sharp (or blunt) the heat shield leading edge or face is. Blunt, Apollo like, reentry shields are very reliable and weigh less than 5% of the reentry mass. The sharp edges needed for really good wings face far higher heat loads and may be impossible.

If you try to read the original NACA work, I offer a few hints. First, in near vacuum, air is actually very viscous, providing laminar flow condition, EVEN AT HYPERSONIC SPEEDS. On Earth, we normally see laminar flow only at low speeds, and turbulent flow at normal aircraft speeds. The space shuttle actually has laminar flow over its wings about halfway through reentry, and then it transitions to turbulent flow, with a thinner boundary layer and somewhat higher temperature. Note also that thermal energy is transferred through a relatively stagnant air layer by molecular motion in very much the same way that “momentum” is transferred through the layer to produce the “skin drag” force from air flowing smoothly across a surface. This linkage of skin drag to heat transfer is a key part of the “Allen and Eggers” paper.

Your “pumped gas” idea also matches the effect of “transpiration cooling” in ablative heat shields. A countercurrent transfer, with the inflowing heat being transferred to an out flowing gas, captures virtually all of the heat in the gas flow. In the ablative heat shield the gas is cooked out of an organic binder as it heats up. Your small holes could be used to feed a stored gas into a porous “felt” of high temperature fibers to get the same effect with a reusable heat shield.

My preferred form of this is a “Ballute” (Balloon – Parachute) trailing a spacecraft to provide reentry drag. If the material is made of a dense, graphite cloth, then the inflation gas will flow slowly through it as discussed. It the material on the spacecraft side is more porous than that on the back (which does not experience the heat loads), then before reentry the gas leaking from the front side will generate a thrust to pull the high temperature attachment cable taught.


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Post    Posted on: Fri Jan 30, 2009 10:12 am
What about using the finding I postedabout yesterday? Scientists have managed to turn Gold harder that should have become a plasma - they used a laser and heated the Gold at 10^15 degrees C per second.

The Gold were a film or layer.

So if this would be done previous to reentry or entry no catastrophic damages like Columbia should be possible.

What about it? How could it bedone? ...



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Post    Posted on: Fri Jan 30, 2009 2:57 pm
At last cheap access to space:- Gold Heat shields. :)

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Post    Posted on: Mon Feb 02, 2009 11:01 am
In the grand scheme of things, gold is quite abundant and cheap! It's the H3 we want. Once we start mining that from the moon, then the profits will pay for all the gold you need.

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