Germany To Test Actively-Cooled Spacecraft 127
FleaPlus writes "The German Aerospace Center is planning to launch a novel reusable spacecraft in 2011, incorporating flat, damage-resistant tiles. Nitrogen will be pumped through the porous tiles, creating a protective gas layer that actively cools and shields the hottest parts of the spacecraft from the searing heat of reentry. The €12.5M unmanned 'SHEFEX II' project is a major technological step toward the team's eventual goal of a reusable space glider, which will be cheaper and easier to build than NASA's space shuttle."
I would hope so (Score:5, Insightful)
German technology (Score:5, Insightful)
Remember, German technology put the first man on the moon.
why the obession with glider spacecraft? (Score:3, Insightful)
There is no need for glider-based spacecraft. Wings are useless in space. "man-rated" launch vehicles cost something like $10k per pound to go to orbit. The extra pounds for wings are a massive waste of money and resources.
The original design--The Capsule--was the right idea! Why not build a re-usable capsule?
Liquid nitrogen? (Score:4, Insightful)
Yeah, and if there's even a slight problem with the coolant system -- the liquid turns to gas, expands 1,500x its original size... and is surrounded by ceramic, metal, plasma, and several thousand degree temperatures at a critical point on the airframe.
What could possibly go wrong?
Re:why the obession with glider spacecraft? (Score:4, Insightful)
The original design--The Capsule--was the right idea! Why not build a re-usable capsule?
You're assuming that all spacecraft have the same mission requirements. The Space Shuttle was originally intended, IIRC, to be able to take things to orbit, and OPTIONALLY RETURN THINGS FROM ORBIT. A space capsule will only be able to return humans and -very small items-. No going to orbit, picking up a broken or obsolete satellite or space telescope, bringing it back for fixes or refurbishment, and returning it to orbit on another flight. If all you're doing is sending stuff up, and then returning only people, then yeah, a capsule can do that job; but that's not the only job that needs doing.
Re:Liquid nitrogen? (Score:0, Insightful)
You are right, we should not do anything at all ever! This is the only way to ensure that nothing ever goes wrong!
Re:why the obession with glider spacecraft? (Score:4, Insightful)
That's mostly a false dichotomy
1. Lifting reentry of a capsule [wikipedia.org] flying at a high angle of attack.
2. In the terminal stage, use parafoil like those tests [wikipedia.org] (did you know that NASA was instrumental [wikipedia.org] in popularising the concept of hang glider [wikipedia.org], etc.?)
Re:German technology (Score:4, Insightful)
Re:Liquid nitrogen? (Score:2, Insightful)
Yeah, and if there's even a slight problem with the coolant system -- the liquid turns to gas, expands 1,500x its original size... and is surrounded by ceramic, metal, plasma, and several thousand degree temperatures at a critical point on the airframe.
What could possibly go wrong?
Which would be why this is unmanned testing.
Re:German technology (Score:5, Insightful)
The reason the Soviets beat us to space is that their German scientists were better than our German scientists.~
Re:why the obession with glider spacecraft? (Score:3, Insightful)
Actually, if you take a look at their basic development strategy [www.dlr.de] (near the bottom of the page), it looks like there's a few different directions they're interested in potentially taking this: a suborbital microgravity platform, a suborbital point-to-point transportation, and orbital transportation. In the case of microgravity research you want to be able to launch often, so returning to a landing strip makes that easier and more economical. Same for point-to-point transportation: if you're delivering cargo or people on a hypersonic delivery craft, you don't want to have to spend time to recover it from the ocean. Finally, for orbital transportation there's convincing arguments both ways, although one benefit of a glider-based reentry is that it tends to have lower G values.
Think of it as ablative cooling by outgassing (Score:3, Insightful)
I've just looked up the latent heat of vaporization of nitrogen and it's 200 kJ/kg [wikipedia]; its specific heat as a gas is around 1.1 kJ/kg/K, so to boil it and heat it to 1000K takes roughly 1.2 MJ/kg. The kinetic energy of an orbiting spacecraft is roughly 30 Mj/kg and even a spacecraft in a vertical trajectory that reaches 200 km has an energy of roughly 2 MJ/kg. So unless the spacecraft consists almost entirely of nitrogen tank, most of the heat of re-entry will have to go elsewhere. I propose that a better way to think about this cooling scheme is that the nitrogen is being ablated as a way to protect the ceramic tiles.
Does this mean it's a bad idea? Noooo! Replacing the ablated nitrogen is as simply as putting a hose in the tank after the craft lands, while inspecting and replacing ablated ceramic is one of the reasons why the Shuttle takes months to turn around (true fact: the most Shuttle missions NASA ever flew in one year was 10, in a year when they had four birds to fly, i.e. 48 bird-months, or 4.8 months per flight). Also, it seems likely that you can adjust the flow of nitrogen to get the temperature you want (within limits) instead of having to design tiles that can take whatever temperature Nature hands you. I wish these guys the best of German luck.
Re:why the obession with glider spacecraft? (Score:5, Insightful)
Indeed -- look at the history of capsules -- the sinking of Mercury 4, the Voskhod 2 crew's night surrounded by wolves, Soyuz 18a's high-G roll that nearly sent it tumbling off a 500' cliff, etc.
I think the best example is Soyuz 23: a mistargetted landing led to the capsule landing on a frozen lake and crashing through the ice. No problem as it was designed to float, right? Well, the parachute got wet and, weighed down, dragged the capsule upside down. The vent tube -- open, as per standard practice -- now began to fill the craft with ice-cold water. The cosmonauts luckily stopped it up before it sent the craft to the bottom. So there they waited, half submerged, upside down in a frozen lake, with no air, in -22C weather. They had to cut way their space suits and get into clothes so as not to freeze; it took an hour and a half. They relied on regenerated air, and did everything possible to conserve power -- they'd leave the system off until they nearly blacked out from the CO2, then turned it on just long enough to clear up. Nonetheless, they still ran out of power. Helicopters couldn't land in the blowing mist, and rescue attempts failed until they ultimately got a hook on the parachute and dragged the craft half a dozen kilometers across the frozen landscape before they could be rescued.
Being able to control where you land is a very good thing. ;)
Re:Weight (Score:3, Insightful)
Re:Think of it as ablative cooling by outgassing (Score:3, Insightful)
You're thinking about all wrong. Yes, the nitrogen is basically an ablative, but you missed a key aspect of reentry: radiative heat loss. Surfaces radiate heat proportional to their temperature to the fourth power. The hotter you can run them without them melting, the faster they radiate. The key point of a coolant isn't to keep the surface *cool*, but to keep it *cool enough* that it can radiate in peace without failing. You can't omit the radiative heat loss.
Re:Liquid nitrogen? (Score:3, Insightful)
However this is not a liquid cooling system of the tiles. The (liquid) gas is pumped through the tiles to the leading edge where it is expected to evaporate. So worst case should be no cooling from the gas or the gas layer as a protective layer between the tiles and the incoming atmosphere.
If designed properly if everything works it is re-useable, and if there is a failure you would hope a production model would be designed to that the tiles would survive a single use even without any gas flow.
Re:Thank God it's unmanned (Score:3, Insightful)
Re:why the obession with glider spacecraft? (Score:3, Insightful)
Not just that. Capsules don't scale well. Building a heat shield that burns up on reentry is fine if you're flying once in a while with three or four people. It doesn't work well for a space plane to carry a hundred people on a daily basis. In the long run, we need something that's truly reusable.
Re:German technology (Score:5, Insightful)
This sums it up surprisingly well, and also explains (while of course ignoring lots of other relevant stuff) why the Soviets
made it up there quite fast, but after this failed to make significant progress for quite a while.
Re:German technology (Score:5, Insightful)
Not at all. All but the first couple post-WWII Soviet rockets were *very* different from the V2. The R1 was basically a V2 replica, but the R7 was based on Korolyov's pre-war designs.
We always seem to be looking for ways to downplay the Soviet achievements in space in the 1950s and early 1960s. Why is that? Is it too much to accept that there were some *really damned good Soviet rocket scientists* over there? Had they not been majorly underfunded compared to the US in the moon race, and had they not made a couple of key design blunders with the N1, they likely would have beaten us in that, too. The loss of Korolyov in the middle of the project didn't help, either.
The reality is that it was the *US* that was heavily reliant on German rocket scientists and German technology, to a much greater extent than the Soviets. We shipped over three hundred freaking train loads of V2 parts back to bootstrap our space program. We took almost all of their top scientists (most Germans were scared of the Soviets, and the US offered big incentives).
Re:why the obession with glider spacecraft? (Score:2, Insightful)
They havent made a movie on this yet?
Hmmm, who would want to see thrillers based on the Russians!
Re:Unless you can land it on a runway who cares? (Score:3, Insightful)
Not that this isn't a great tech demonstrator but why build a capsule that has a reusable heat shield? So you go through all of this trouble to build a beautiful reusable heat shield than slam it into an ocean or desert?
There's a few possibilities. One is to use retrorockets, which are fired immediately before hitting the ground to give it a gentler landing. Another possibility that Boeing's seriously considering for their crew capsule is mid-air recovery (like that used on a number of unmannned return missions), where the capsule is caught by a helicopter as it's parachuting downwards, and can then be gently returned to a landing pad.