The perfect fire-proof material?

[Pipcard]

Starlite:

[ame="http://m.youtube.com/watch?v=W4nnLP--uTI"]Maurice on Tomorrows World - YouTube[/ame]

Too bad its creator, Maurice Ward, never revealed the formula (except, apparently, to his family) before he died.

 

[Urwumpe]

Too bad its creator, Maurice Ward, never revealed the formula (except, apparently, to his family) before he died.

So, we can deduct, this formula is likely not as much important as the presentation of it.

Also, what is known by the technobabble of it, sounds very unlikely to have any of the physical properties claimed. There is no experimental evidence. Only show.

And what is told in the show is not really impressive if you ever worked with blowtorches or lasers.

Also... have you EVER seen the demonstrations of the Space Shuttle TPS material? You might be impressed, what was already possible in 1970.

 

[Spacethingy]

Sadly, you can't really beat asbestos, apart from in one very obvious department.

 

[MaverickSawyer]

Actually, asbestos in small amounts will NOT cause issues. Most types of asbestos will dissolve in your lung over the course of about a year, if in small amounts. LARGE amounts are not good for you, no matter what type. I even have a small sample of asbestos on my bookshelf (it's cemented by calcite, but it's still cool )

Thank you, Geology 400 at the local community college.

 

[jedidia]

It's interesting you should bring this up, since I heard about this quite recently and was intruiged by it.

What confuses me a bit are the tests. From what I was led to understand by different articles, the stuff has actually been tested by at least two instances and its property confirmed, but I'm not quite sure on that.

The trouble is, we really don't know the limits of the stuff... It could be that it's not much more superior to other coatings we know, but the fact that an amateur chemist is able to cook it up in his kitchen would probably mean that it would be a lot cheaper. NASA needs (sorry, needed ) a special kind of superglue to paste their ceramic tiles on the space shuttle which in itself seems to be more expensive than gold.
If the thermal protection could just be cooked up in an uncomplex process and be painted on stuff, that sure would reduce the costs a bit (and would be a breeze to repair on orbit... well, if you consider getting to the bottom of the space shuttle a breeze. As far as I'm aware, that maneuver was a no-go during the entire STS service. I'm not sure if they did it during the MMU tests, though).

If the stuff would be usefull to reduce the heat absorbed by combustion chambers of thrusters it could also mean a slight increase in engine efficiency, but the properties are simply not known well enough to confirm that.

Anyways, I decided to employ it in my science fiction scenarios to keep my fusion engines from melting without ridiculous core radiuses, so there's that

 

[Urwumpe]

If the stuff would be usefull to reduce the heat absorbed by combustion chambers of thrusters it could also mean a slight increase in engine efficiency, but the properties are simply not known well enough to confirm that.

That is for example a missunderstanding - often you actually want to absorb some heat energy to increase the efficiency - by heating the fuel close to the flash point and thus have higher combustion temperatures.

Heat is not that much a problem on a rocket engine, since you can easily manage it. if you would not die of the sound pressure, touching a running SSME would result in severe burns. But not because of heat, but because the outside of the engine is cryo-cold.

 

[Thorsten]

But not because of heat, but because the outside of the engine is cryo-cold.

From what I have read recently, the SSME relies on pre-combustion to drive the high pressure turbo pumps, and that seemed to have the implication that both the flow of fuel and oxidizer into the combustion chamber and the diverted flow of gas cooling the engine is not at cryo but roughly at room temperature - which is still much cooler than the exhaust gases. So I guess the low pressure parts of the engine are cryo-cold, but anything after the pre-combustion is really not.

If the thermal protection could just be cooked up in an uncomplex process and be painted on stuff

One important purpose of thermal protection is that there's an aluminum structure somewhere which makes up the airframe (spaceframe?) of a re-entring body, and that can't take too much thermal load before it loses stability. At the same time, there's aerodynamics being important, and the outline and surface roughness of a spacecraft in a non-ballistic entry should not change (that's why the shuttle can't have ablative heat shields, because the char changes surface roughness).

The shuttle nose and leading wing edges are of a material (RCC) that keeps its form when very hot - that satisfies b), so it will preserve aerodynamics when you heat it, but not a), it doesn't keep the heat from the structure behind, and there's extra insulation to accomplish that. The ceramic tiles are a different beast - they take less thermal load, but have a low heat diffusion coefficient, so they have a hot outer and a cool inner surface, but they would not work on the nose as they can't take much force.

Anything you can simply paint on might be able to withstand heat and preserve surface roughness, but it'd be way too thin to protect any structure behind it from heat - if the backside of your paint gets as hot as the front side which is the case for a thin layer, you don't gain anything. And I completely fail to see how anything you can paint on would be structurally stable, i.e. be able to carry aerodynamical force load like the Shuttle wing edge obviously does.

 

[jedidia]

if the backside of your paint gets as hot as the front side which is the case for a thin layer

But that's exactly what starlite advertises... Whether or not it could keep those promises is pretty much an unknown, though.

 

[Thorsten]

So where's the heat going? Thermal energy goes somewhere - always. I can see where it goes in an atmosphere when there's convection available to dump it into the air, but where does it go in a near vacuum?

In a layer of paint, you have close to zero mass, so there's no actual heat capacity even if the specific capacity is high. So it can't get stored and dumped over time - it has to be dealt with now. It can't be convectively transported. You might be able to radiate it if the material gets hot enough - you can do the numbers and see how high a temperature you need for that.

 

[Urwumpe]

From what I have read recently, the SSME relies on pre-combustion to drive the high pressure turbo pumps, and that seemed to have the implication that both the flow of fuel and oxidizer into the combustion chamber and the diverted flow of gas cooling the engine is not at cryo but roughly at room temperature - which is still much cooler than the exhaust gases. So I guess the low pressure parts of the engine are cryo-cold, but anything after the pre-combustion is really not.

You guess wrong.

(Sorry for the large photograph, but there is no smaller version of it)

Thats ice that separated from one of the main engine nozzles after MECO.

Also, the outer wall temperatures of the SSME nozzle or other parts are known by SSME simulation models:

Variable | State | Description | Units | 65% RPL | 100% RPL | 104% RPL | 109% RPL
t_4||Fuel temp. inside nozzle HE|R|449.5|465.8|456.4|448.1
t_5||Fuel temp. inside MCC HE|R|509.0|466.0|455.9|443.1
t_9||Preburners fuel supply line temp.|R|295.4|276.4|276.4|276.5
t_op||Oxidizer preburner temperature|R|1,057.0|1,440.3|1,475.8|1,517.6
t_fp||Fuel preburner temperature|R|1,633.5|1,753.9|1,796.1|1,854.8
t_fi||Fuel injector temperature|R|1,392.7|1,560.7|1,593.1|1,636.2
t_c||Main chamber (MCC) temperature|R|6,400.0|6,400.0|6,400.0|6,400.0
tw_15|X|Hot wall temp. at MCC HE|R|1,228.8|1,214.9|1,203.1|1,187.1
tw_25|X|Cold wall temp. at MCC HE|R|509.0|466.0|455.9|443.1
tw_14|X|Hot wall temp. at nozzle HE|R|1,162.5|1,260.3|1,250.4|1,244.5
tw_24|X|Cold wall temp. at nozzle HE|R|449.5|465.8|456.4|448.1

The unit R is rankine, 1 R = 5/9 K. The temperatures at the heat exchanger (HE) cold walls are between -20°C and -15°C. Even if the MCC temperature is 3282°C.

---------- Post added at 12:16 PM ---------- Previous post was at 12:14 PM ----------

In a layer of paint, you have close to zero mass, so there's no actual heat capacity even if the specific capacity is high. So it can't get stored and dumped over time - it has to be dealt with now. It can't be convectively transported. You might be able to radiate it if the material gets hot enough - you can do the numbers and see how high a temperature you need for that.

Most fireproof paints used in buildings or spacecraft heatshields are using endothermic chemical reactions. Those don't work for all eternity, but can keep things cold for minutes.

 

[C3PO]

Rocket engines: So hot they're cool!

 

[Thorsten]

You guess wrong.

Why would that be? Your numbers pretty much back me up...

The fuel line has a temperature of about -120 °C - that's what I'd call a cryo temperature.

The temperatures at the heat exchanger (HE) cold walls are between -20°C and -15°C.

Yeah, compared with the boiling point of liquid hydrogen in the tank, and 3200 °C in the chamber, -15°C is really different from 'roughly room temperature'... I can totally see that. I'm 30 degrees off in my 'guess' in a temperature range of several thousand degrees - that's an accuracy better than a percent.

Have you ever touched something at -20°C? I live in central Finland, that's winter temperatures for me (not right now obviously, but we had up to -36°C two years ago). Doesn't burn you when you touch things, it's just painfully cold. If you touch something at -120°C, that really burns you (well, if it's liquid nitrogen, then it might vaporize before...).

Most fireproof paints used in buildings or spacecraft heatshields are using endothermic chemical reactions. Those don't work for all eternity, but can keep things cold for minutes.

I sort of said that, right? But char doesn't do for aerodynamics, it doesn't char in a controlled way.

 

[jedidia]

In a layer of paint, you have close to zero mass, so there's no actual heat capacity even if the specific capacity is high. So it can't get stored and dumped over time - it has to be dealt with now. It can't be convectively transported.

Yeah, wondering how that would work under actual reentry conditions is one of the things I was wondering about, and about which we have no data...

I figured when there's enough air to create serious friction there might be enough air for effective convection, but while I understand basic thermodynamics, I am absolutely clueless about the conditions on re-entering...

Most fireproof paints used in buildings or spacecraft heatshields are using endothermic chemical reactions.

Endothermics... another thing I don't have a clue about

 

[Urwumpe]

Endothermics... another thing I don't have a clue about

You put energy into it, and when the reaction happens, you get much less energy back than you put into it. Like turning water into hydrogen and oxygen. or fusing iron atoms.

Or you can think of a simpler endothermic reaction example, if you leave chemistry behind: When you sweat, you cool down. Why? Because turning water into steam takes about 500 times more energy than heating it by one degree. (And when you condense water again... the energy comes back, an important detail for our weather)

Such a paint does have a pyrolysis reaction, but the reaction generates less energy, than the fire had to put into it, the material cools down during the reaction.

Next, you can also have an extremely low thermal conductivity by such reactions. The outer layer heats up, reacts, cools down and slowly heats up again, slowing the process for the next layer inside... etc. also, often, the reaction results in a decrease in density and increase in volume, again slowing thermal conductivity down a lot.

That is one aspect how spacecraft heat shields work today. The next aspect is carrying as much energy as possible away from the heat shield by storing it into the released products. Like only letting liquid drops of the heat shield fall away or vaporize, after storing a lot of energy (by low viscosity for example).

If every kg of heat shield stores away more than 30 MJ of energy before it leaves the spacecraft , you could reenter already without convection or radiation.

Next, any better heatshield only takes 0.5 % of the energy generated by aerodynamic heat flux. The majority stays with the air and mostly what the plasma radiates back at the spacecraft, and what is not instantly reflected away by the heatshield, adds energy to the spacecraft, so you only need more than 152 kJ/kg . in relation: Turning water into steam takes 2,260 kJ/kg. And that already shows why water is a poor heat shield material. Even with perfect values for reflection and thermal conductivity, water would be too heavy and takes too little energy away in the steam (especially if you have low ambient pressure)

And more important is the time - if you have a lot of energy in a short time, the heat shield reacts too slow and does not have the desired reactions. Pure phenolic carbon for example has only 300W/cm², enough for LEO reentries, but just too heavy.

PICA, one of the best ablative materials known, can handle 1200W/cm² heat flux - this even works if you enter Jupiters atmosphere directly.

 

[Thorsten]

Next, any better heatshield only takes 0.5 % of the energy generated by aerodynamic heat flux.

That must be dependent on how the shockwaves are arranged - I _guess_ that that's true if the shockwave is detatched but not when the shockwave is at the surface.

But thanks for the number, I've deduced something like that from comparing blackbody radiation temperature for given heat flux in my atmospheric entry simulation code with actual numbers quoted for peak temperatures, and found that I need a really low transfer coefficient to get to the real numbers. You may be amused that the number which I have in is 1%.

 

[Urwumpe]

That must be dependent on how the shockwaves are arranged - I _guess_ that that's true if the shockwave is detatched but not when the shockwave is at the surface.

Blunt body, blunt end forward. Which also applies to the Space Shuttle with some exceptions at the edges.