You are not logged in.
Pages: 1
I thought we should have a thread on thermal protection so I am creating this one. I don't really have to much to say on it at the moment but I find the range of methods to deal with thermal protection quite interesting including: RCC, ablative heat shields, active cooling and vehicle shape. I have noticed that the faster vehicles seem to be smoother have rounder noses and less of a wing if any wing at all. Some vehicles I would like to see discussed in this context are both the Boeing CEV, the Lockheed Martin CEV, the russion clipper, the space shuttle, the x-37 and the hyper x.
All of these vehicles except the hyper-x travel at Mach 25 or faster. I presume the hyper-x will have need a new shape for higher speeds. However because a scram jet would have slush hydrogen cooling perhaps it wouldn't have to have as smooth a shape as other vehicles.
I find the ablative heat shield interesting and I would like to know why you can't just spray it on a reusable launch vehicle like you could spray wax on a car. Is it impossible to mix this technology with the RCC tiles. Perhaps just enough of a coating to deal with the heat loads until the vehicle slowed to under Mach 25.
I am also told that the RCC tiles sublimate all at once when they get to hot. I find this property rather unusual. So it takes next to no energy to sublimate the tiles once they reach a certain temperature. Kind of like how a super critical heated coffee could explode once you take it out of the microwave.
Anyway, I hope this is enough to get some discussion started. I am interested in learning more about thermal protection
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
Offline
An ablative coating isn't like a paint job, because the way it keeps the vehicle cool is by intentionally burning it off, which makes it by nature pretty heavy. You need alot of it to protect your vehicle, such as the shield on American and Chinese capsules is several inches thick, and must be applied carefully to avoid weak spots.
For a spaceplane, dry mass is absolutely critical, and will make-or-break if it is practical or not. Having to lug a thick layer of ablative material even a centimeter or two thick is probobly not happening.
The mass problem asside, a truely "no kidding" reuseable vehicle will simply have to have a fully reuseable heat shield, good for at least a dozen or two flights. It is simply too expensive and too slow to re-do an ablative shield between flights.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
the good majority of the problem is design, the black bird is almost the perfect example...
surprisingly enough, thats a really small plane... BUT its designed great. the edges are VERY thin to reduce heat resistance and cut through the air as much as possible.
if you look at thermo graphs of it in flight, you will see how hard it is to take care of the thermodynamics of it in flight. it has to go through insanely extensive testing to make sure it is as aerodynamic as possible before it can start going at those higher speeds...
in all honesty, a needle shapped pod would probably work best. just add a large rocket to the back... but then you have to wory about the front temperature.
you could always use something like a refridgerator on the edges...
Offline
A space vehicle reentering from trans-lunar velocity will be going ten times the speed of the Blackbird though, it is an entirely different set of circumstances. A pointy needle shape is no good, because you DON'T want to slice through the air, because that means the air will be in contact with the vehicle's skin, and will become way too hot and melt.
The way that you want to reenter is to hide the vehicle behind the shockwave produced by the superhigh speeds as much as you can. This means a stubby, blunt vehicle that the air will pile up against like a capsule or a lift-body.
Active cooling by pumping a refrigerant against the skin has been proposed, but those systems are usually much heavier and prone to problems since you have to pump the fluid very reliably.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Over here in Scotland a private research organisation conducted a lot of research into what was called Waveriders. They used the Shockwave and where able to enter at a much steeper descent. Most designs where variations of slightly rounded triangles.
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
Offline
Over here in Scotland a private research organisation conducted a lot of research into what was called Waveriders. They used the Shockwave and where able to enter at a much steeper descent. Most designs where variations of slightly rounded triangles.
that could be something to work on too... something like a partical shield to block against stuff...
Offline
FWIW, "The Rocket Company" had a nice list of heatshields, some quite outlandish... Ranging from wooden blocks to phase changeing salts heatshields...
(Waybacklink:)
http://web.archive.org/web/200401041254 … page1.html
Offline
to cross fertilize a bit on the subject, i include the slashdot comments
http://science.slashdot.org/article.pl? … 160&tid=14
or get the info straight from horses mouth http://www.cip.csiro.au/AAV/index.htm
play with me! [url]http://www.augmenton.net[/url]
Offline
to cross fertilize a bit on the subject, i include the slashdot comments
http://science.slashdot.org/article.pl? … 160&tid=14
or get the info straight from horses mouth http://www.cip.csiro.au/AAV/index.htm
I don't see what these links have to do with heat shields.
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
Offline
I think the other link in the page has a little to do with a means to self repair the what would be akin to the shuttle RCC tiles.
Ant logic makes sense in space
A spacecraft skin is being developed that assesses the severity of any damage it suffers from space debris and other impacts. The project, which is inspired by the behaviour of ants, is seen as the first step towards a self-repairing craft.
NASA on the project and has so far created a model skin made up of 192 separate cells. Behind each cell is an impact sensor and a processor equipped with algorithms that allow it to communicate only with its immediate neighbours.
The second link is the corporate page that references the sensor array used to trigger when it should try to self heal the outer shell of the space ship.
Offline
Well, you sure aren't going to be auto-repairing the heat shield while you are using it, though it would be nice if you could pinpoint damage quickly.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Supposedly the Chinese used wood as an ablative coating. Supposedly cork. Do you guys know where I can find any research published using cork as an ablative?
$2 million bucks are riding on half a dozen eggs landing intact---this could be the key.....
FunkyJ
Offline
Its more like Balsa wood
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
The Mars rovers used such a combination heat shield to land on Mars, possibly some references may be available from Nasa, Lockheed or even from Boeing on the use of cork.
Offline
NASA uses cork as an insulator against cyrogenic temperatures, but not as an ablative heat shield I don't think, only China does that.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Kinda hard on the cork trees to use that for any sort of mass-use space travel.
Re-entry really is *the* problem for reuseable SSTO craft. The mass fraction is doable if you don't need to lug around all that cooling. Here's an idea: an aerogel heat shield protected on takeoffs by a disposable shroud. They have new carbon aerogels... trying to find the melting point, it should be lower than straight carbon, but not by much. Or perhaps... nevermind, this idea has already been looked at. NASA's Jet Propulsion Laboratory is looking at non-ablative aeroshells that is sort of a sandhich of carbon-carbon, silicon carbide, and carbon aerogels. No ablation, no problem - the materials have melting points from hell and the aerogel insulated very well to boot.
Offline
I disagree, the mass fraction is very much still problem #1.
The Tiokovski rocket equation demands that your rocket's total mass empty not exceed 9-11% of the mass full, using the ideal fuel of liquid hydrogen.
That 9-11% has to include everything, the engines, the fuel tanks, and the payload. Since Hydrogen is so bulky, its tanks have to weigh quite a bit. Overall, you are left with a vehicle that isn't more then a percent or two payload tops, which will of course be a huge vehicle.
And thats without extra fuel for landing.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
I disagree, the mass fraction is very much still problem #1.
The Tiokovski rocket equation demands that your rocket's total mass empty not exceed 9-11% of the mass full, using the ideal fuel of liquid hydrogen.
That 9-11% has to include everything, the engines, the fuel tanks, and the payload. Since Hydrogen is so bulky, its tanks have to weigh quite a bit. Overall, you are left with a vehicle that isn't more then a percent or two payload tops, which will of course be a huge vehicle.
And thats without extra fuel for landing.
I agree, we don't have the mass fraction problem solved yet, but for the first time I feel like 10% dry mass might be doable. With composite/aerogel fuel tanks and prehaps a CNT/Buckball thermal protection system, both materials that should be within the state of the art within a decade or two might be able to solve the problem, or at least get close enought that as you put it a true 'no kidding' tsto should be a very workable technology. Of course if you can pull of Scram jets on the first stage you can throw the rocket equation out the window to a certain degree.
Offline
Oh I think that we could do TSTO right now today if we put our mind to it, particularly burning slushed Hydrogen or Methane instead of liquid hydrogen for the upper. No scramjet required, just a really big carrier plane with rockets or turbo/ramjets (ala SR-71).
A scramjet SSTO spaceplane has some pretty serious issues that need to be addressed before it would be practical, and is pretty far down the road. Twenty years wouldn't be an excessive estimate, barring a hyper-expensive crash program.
An SSTO with composite/aerogel fuel tanks, something like the DC-X (not so sure about the soft landing bit), would be possible, perhaps a bit easier then a Scramjet SSTO, particularly burning slush Hydrogen or with a bipropellant arrangement with Methane.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
Offline
Pages: 1