Germany To Test Actively-Cooled Spacecraft

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."

Comments

I would hope so

[SigNuZX728]

"...will be cheaper and easier-to-build than NASA's space shuttle." I would hope they could build something cheaper and easier than the 30-plus-year-old shuttle.

German technology

[Anonymous Coward]

Remember, German technology put the first man on the moon.

Re:German technology

[headkase]

It may be flamebait, yes, BUT there is a measure of truth in that post.

Re:German technology

[aquila.solo]

There's plenty of truth in that post.
The reason the Soviets beat us to space is that their German scientists were better than our German scientists.~

Re:German technology

[Rei]

That's not entirely true; it's more of a US excuse during the space race. The US was very successful with Operation Paperclip, which was an attempt to make sure that the US, not the USSR, got most of the German rocket scientists (as well as several whole V2 rockets). The Soviets got a few German rocket scientists (most notably, Helmut Gröttrup, Wernher von Braun's assistant), but not many. Most of the people they got were low level people, mainly on the assembly lines. They were primarily interrogated for information and little used beyond that point. After 1951, not even Gröttrup was allowed to assist in their rocket program any more, and he was returned to Germany in 1953 -- back when von Braun was just starting to become a big rocketry name in the US, and well before his tenure as NASA's first director (1960-1970).

Re:German technology

[paeanblack]

Remember, German technology put the first man on the moon.

Ven the rockets are up, who cares vere they down?
"That's not my department", says Wernher von Braun

"In German oder English I know how to count down,
Und I'm learning Chinese," says Wernher von Braun

Re:German technology

[the_other_chewey]

There's a nice bon mot about this: "The Soviets got the Germans who knew how it worked, the US the Germans who knew why it worked."

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

[Rei]

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:German technology

[Anonymous Coward]

I always thought the Soviets and the Americans both got there because they put the time and money into the problem, and that the Soviets got there first because they put more time and money into it at first.

Strictly speaking, Von Braun's engineers were the first to make practical ballistic missiles, and that's about it. They contributed to the Soviet and American rocket programs, and may even have been critical to those programs in the very early days. That doesn't mean that Nazi-era German engineers are somehow responsible for or instrumental in the success of the programs into the 1950s, 60s and 70s. It seems _very_ much more likely that native Soviet and American engineers deserve that credit.

As an aside, why do you claim the Soviets 'failed to make significant progress for quite awhile'? The only program failure of theirs I can think of is the N2.

Re:German technology

[Anonymous Coward]

The US propaganda machine makes going to the moon such a great thing. But it's pretty clear that getting into space is the major technology hurdle, the rest is just optimisation. The Russians won the space race, getting to the moon is an optimisation.

Just my two cents.

Re:German technology

[Anonymous Coward]

We wouldn't have needed German anything had not the stupid US public not ridiculed Goddard, who was decades ahead of his time.

Re:German technology

[Rei]

Really, had the N1 development process been fully prioritized and properly funded, it could have been an excellent craft. The lack of testing made it poorly handle failures which, when you have that many engines, is almost inevitable. Each time, a single problem took down the whole craft. But the craft was very innovative -- staged combustion engines arranged in a way that formed a primitive aerospike airbreather, for example. Pre-heated fuel from the regenerative cooling was preburned to run the pumps (more common now, but rare then), and the engines were operated fuel-rich. Air, and later O2, was pumped into the hole at the center of the engine ring to burn in the fuel-rich exhaust. The engine ISP on the upper stage was much lower than that of the Saturn V because they didn't use H2, but because of the innovative design, the payload difference wasn't all that huge (130 tonnes vs. 95)

Re:German technology

[Anonymous Coward]

That's because that department was Sanger's...

Think of it as Silverbird 2.0.

Pun aside...

[Anonymous Coward]

...what's really cool about engineering is that there's always another, better way to do it, waiting to be found.

Verstumpt!

[Anonymous Coward]

unter Gleben Glauben Globen!

Zeinen,
Fritz Der Blitzed!

why the obession with glider spacecraft?

[Rocket_Sci]

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?

Re:why the obession with glider spacecraft?

[Bruce Perens]

Re-entry heat shields are useless in space too, just as landing gear are useless for flying!

:-)

I think you want them for the same reason that we don't all parachute to our destination when our plane gets there. Although I can't say I haven't been tempted.

Re:why the obession with glider spacecraft?

[Somegeek]

Capsules are great if you don't mind landing in an ocean or a desert; someplace big and empty.

However, if you would like the efficiencies created by being able to land your spacecraft someplace specific and useful near a population center, like a spaceport or airport, than wings are just the ticket.

Re:why the obession with glider spacecraft?

[Tumbleweed]

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:why the obession with glider spacecraft?

[couchslug]

There is currently no need for MANNED spacecraft, because supporting humans limits their ability to do "everything else" including actual exploration.
The glacial development cycles mandated by the need to return meat tourists cost so dearly that useful "remote manned" missions won't be funded.

Re:why the obession with glider spacecraft?

[baldusi]

Because the USAF wanted the Shuttle to be able to use the atmosphere to break and turn back. This way, when launched in a polar orbit, it would be able to turn back and capture GLONASS or Russian Spy Satellites without appearing on the russian radar. Of course, the final design wasn't able to do such a manouver so the USAF has no use for it. But the design stick.

Re:why the obession with glider spacecraft?

[Anonymous Coward]

There is a huge need for a MANNED spacecraft. I've got a few thousand bucks. I want a ticket to space. I'm sure there are concervatively a few hundred million people with the same desire.

Re:why the obession with glider spacecraft?

[sznupi]

That's mostly a false dichotomy

1. Lifting reentry of a capsule flying at a high angle of attack.

2. In the terminal stage, use parafoil like those tests (did you know that NASA was instrumental in popularising the concept of hang glider, etc.?)

Re:why the obession with glider spacecraft?

[sznupi]

"Needs doing"? If there's one thing at which Shuttle was great, it was demonstrating how its defining capabilities are mostly useless.

Apart from "broken or obsolete" don't forget "space weathered."

Re:why the obession with glider spacecraft?

[phantomcircuit]

Without the ridiculously over-sized they wouldn't have gotten DoD funding.

http://en.wikipedia.org/wiki/Space_Shuttle_design_process#Air_Force_involvement

Re:why the obession with glider spacecraft?

[FleaPlus]

Actually, if you take a look at their basic development strategy (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.

Re:why the obession with glider spacecraft?

[sznupi]

Considering orbits of GLONASS satellites (and probably many spy ones), simple orbital mechanics make performing such mission in a covert manner an impossibility; nvm the inability of the design to break LEO.

Plus so simple and effective countermeasures, from so cheap and numerous (comparatively) "targets" - maybe millitary intelligence works after all, sometimes ;) (not quickly enough to not give us Shuttle though)

Re:why the obession with glider spacecraft?

[sortius_nod]

1. Sure, but you need a large expanse to crash into as per GPs post.

2. Sure, but it's an unmanned space craft. And needs to land in a great expanse.

You've ignored exactly what the GP said, and gone off on a self promotion journey. Your points are moot as your response is redundant.

I give you an F for effort and an F for content.

Re:why the obession with glider spacecraft?

[sznupi]

How much for a pony waiting for you at the orbital station?

Re:why the obession with glider spacecraft?

[sznupi]

What are you babbling about? 1. gives quite nice determination of geographic area (it's good enough for Soyuz capsules to be often recorded on video while descending on parachutes by retrieval crews, so quite exact) 2. Have you read even a snipped of those links? Those were tests of a recovery system for a manned spacecraft.

Re:why the obession with glider spacecraft?

[Nadaka]

Kinky... ;)

Re:why the obession with glider spacecraft?

[Rei]

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:why the obession with glider spacecraft?

[Rei]

To space or to orbit?

For "a couple thousand bucks", you're going to have to wait for non-rocket methods of launch.

Re:why the obession with glider spacecraft?

[peragrin]

It is one thing I wish they would save a shuttle for.

NASA as a publicity fund raising stunt should save one shuttle's worth of parts and go retrieve the Hubbell Space telescope instead of crashing it into the ocean. Have the shuttle land and the load it directly for a flight to DC. Giving the whole pile (shuttle with Hubbell inside) to the Smithsonian.

Now that would be an awesome display. Heck I would donate money to help make that happen. To bad NASA doesn't think like awesome anymore.

Re:why the obession with glider spacecraft?

[aliquis]

Why do we need to get people back here in the first place?!!

(Maybe we could even make a religious tweak, such as:
1) Sign up and end your life as an astronaut, become a hero!)
2) Shoot people up in space when we need something fixed.
3) Let them fix it.
4) Leave them.
5) Profit!

Maybe China will pick up my excellent idea?!

Re:why the obession with glider spacecraft?

[dgatwood]

However, if you would like the efficiencies created by being able to land your spacecraft someplace specific and useful near a population center, like a spaceport or airport, than wings are just the ticket.

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:why the obession with glider spacecraft?

[DerekLyons]

+4 Interesting? This not only isn't interesting - it's utter and complete innumerate and ill educated hogwash.
 
The Shuttle cannot 'turn back' once it reaches orbit (thus avoiding Russian radars). It can 'turn back' in the atmosphere (shortly after launch), but in that event it gets nowhere near orbit and thus cannot snag a satellite.
 
What the USAF wanted the Shuttle to do was do a 'one orbit' launch out of Vandenburg, inspect or grab a Soviet satellite, and then landing again in US territory. The problem is that the Earth's rotation moves California to the east by a thousand miles or so - which meant the Shuttle would be landing in the ocean. The solution was to use aerodynamic flight during re-entry to maneuver to the east. So the USAF required that NASA enlarge it's existing wing to accommodate this in exchange for the USAF's political support.
 
Even though the mission was never flown, that has more to do with the inability to open and the close the bay doors fast enough, as well as accomplishing other tasks, to shift modes between launch -> orbit -> re-entry than anything else.
 
As a side note, this USAF requirement had less of an impact than urban legend would like to believe. NASA was already enlarging the wings to add cross range capability for safety reasons. More cross range means landing windows (at the recovery sites) are longer and occur more often, makes certain abort scenarios easier (notable Trans Atlantic Abort), and increases the availability of emergency fields.

Re:why the obession with glider spacecraft?

[Anonymous Coward]

damn wish i wasn't an AC... MOD up parent and post this somewhere on Colbert's message boards!

Re:why the obession with glider spacecraft?

[Anonymous Coward]

Of course, there are much cheaper ways of controlling your landing, like parafoils. You don't need a big heavy wing all the way down.

Re:why the obession with glider spacecraft?

[strack]

yeah, and how bout that time that some of the large, intricate and controllable reentry system of the columbia got knocked off, and THE ENTIRE FUCKING CREW OF 7 DIED ON REENTRY.

Re:why the obession with glider spacecraft?

[Rei]

Or the time when the Soyuz crew asphyxiated before reentry. Things can always go wrong in orbit. But what do these things have to do with controlled versus uncontrolled landings?

Re:why the obession with glider spacecraft?

[Anonymous Coward]

They havent made a movie on this yet?
Hmmm, who would want to see thrillers based on the Russians!

Re:why the obession with glider spacecraft?

[ultranova]

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.

I suspect this has to do with the idea that anything except Single Stage To Orbit And Back is not a "real" spacecraft. And that requires controlled landing, which requires either power to slow descend or wings to glid with.

Basically, the designers remember those old (and new) sci-fi shows that have spacecraft that can land, take off, land again, take off again... with just some refueling somewhere along the line. And they are right: being able to do that would dramatically lessen the cost of space travel. Unfortunately, the limits of chemical power very likely make this impossible for anything short of a Nuclear Lightbulb design. And of course a Nuclear Lightbulb doesn't need wings, since it can do a powered landing with engines alone.

So, until we get rid of this childish fear of "nukular! wahh!", and actually build the NL SSTOAB rocket, expect to see lots more of such designs.

The original design--The Capsule--was the right idea! Why not build a re-usable capsule?

The Capsule is basically a reinforced airtight room with some heat protection at the bottom. It doesn't make sense to make that re-usable, especially since making it disposable allows you to use ablative heat protection, which is pretty much idiot-proof.

BTW. There sure has been a lot of space stories lately. I guess things are really starting to get moving again.

Re:why the obession with glider spacecraft?

[Anonymous Coward]

I think you want them for the same reason that we don't all parachute to our destination when our plane gets there. Although I can't say I haven't been tempted.

It beats standing in lines for TSA inspection by a mile or even two. Three miles starts to get dangerous, though.

Re:why the obession with glider spacecraft?

[Anonymous Coward]

Hubble can not be returned with any of the remaining space shuttles - they all have an airlock to dock to ISS permanently mounted in the payload bay. The last shuttle that would have had enough room to transport Hubble would have been Columbia.

Re:why the obession with glider spacecraft?

[sznupi]

Well, with "spaceplane" your're adding the amount of things to go wrong.

For example, asphyxiation that you mention is surely a hazard with all approaches (well, not really anymore, when everybody uses pressure suits). But failure of systems actively controlling descent (which does happen on Soyuz from time to time) - and the results are quite dramatically different.

Re:why the obession with glider spacecraft?

[sznupi]

Now, consider what happens to a spaceplane in such scenarios - a need to ditch (this was considered a loss of crew for the Shuttle); "landing" in wilderness; or relying on succesfull automatic recovery in the case of launcher failure during ascent (hm, where did I hear about such scenario in a spaceplane...) & with recovery systems working perfectly, despite discrepancy between assumed and encountered acceleration on the order which torns apart winged vehicles. Also, take note of how good winged vehicles are at landing on mountain slopes/etc. - they do have to perform such "landings" sometimes.

Soyuz 23 is indeed a good example, but you completelly glance over the background - not uncontrolled, "mistargeted" = a failure of control system / mistake in engine thrust, error of mission control in targetting the landing area, very harsh weather and extremelly strong winds. All those things being outside the scope of the design of reentry vehicle. They just sometimes happen. And for a spaceplane would mean not even really attempting anything which can be called "landing"; the end result would be probably much more catastrophic.

Really, what you are doing is just providing examples of robustness in KISS approaches. Being able to control where you land is a very good thing indeed, one which Soyuz does quite well. As a bonus, if something goes really wrong, there's a high chance of survival.

Re:why the obession with glider spacecraft?

[sznupi]

Did you miss how this story is about non-ablative ("non-burning") heatshield? Also, while capsules might have some not too big size limit (we're probably nowhere near yet), there's also another approach without wings - lifting bodies; which aren't that dissimilar to a capsule flying lifting reentry, just a bit more optimised one... But no wings.

Re:why the obession with glider spacecraft?

[mgblst]

Difficult to cram a love interest in there as well, without making it gay.

Re:why the obession with glider spacecraft?

[dgatwood]

IIRC, what matters most as far as how much heat per square inch during reentry is the mass to surface area ratio. A wing-based design allows you to have minimal support structure for a large portion of the vehicle, which allows you to add a lot of surface area without adding a lot of mass.

Even with a non-ablative heat shield, a capsule design still gets insanely hot on the outside. I'm pretty sure you'd end up having to change the tiles out fairly frequently or the material is going to fracture from the differential heating. Most materials don't like having somebody shoot liquid nitrogen at one side of it and a flamethrower at the other.... I could be wrong. Either way, IIRC, the material should last far longer with a wing-based design, assuming you don't go overboard on the structural steel.

Nitrogen?

[caspy7]

I'm sure it's a lack of understanding the chemistry/physics of the situation on my part, but if nitrogen gets too hot doesn't it become explosive? (a la nitroglycerin)
Is that not a possibility here?

Re:Nitrogen?

[Anonymous Coward]

Yeah, I'm sure that is one of the reasons people are so concerned about global warming.

Re:Nitrogen?

[aquila.solo]

In short, no.

Nitroglycerin is formed by mixing nitric acid and sulfuric acid (both highly concentrated, purified forms).

Atmospheric nitrogen, on the other hand is remarkably stable. At very high temperatures, (such as you might find at the leading edges of a reentry vehicle) nitrogen can be oxidized to to various forms of NOx. These can form acids in solution, but not in concentrations high enough to worry about.

And when you consider that there is plenty of naturally-available nitrogen in the atmosphere, this small addition probably isn't enough to worry about.

Gary Hudson

[Bruce Perens]

I saw Gary Hudson present a similar proposal at a members-only conference some years before Rotary Rocket.

Re:Gary Hudson

[Anonymous Coward]

I saw Gary Hudson present a similar proposal at a members-only conference some years before Rotary Rocket.

At that conference, did you see a bit out-of-place looking person wearing lederhosen?

Re:Gary Hudson

[dougisfunny]

Or perhaps a dirndl judging by the article picture.

Re:Gary Hudson

[AJWM]

You're probably talking about the transpiration cooling that Gary proposed for his Phoenix series of SSTOs. That would have worked even better than nitrogen gas cooling, given the extra heat soaked up by the water flashing to vapor. The transpiration cooling struck me as tricky because of the complex fabrication required (although much more do-able these days than in the '80s) and the need for high-purity coolant so that you don't get residue plugging the transpiration orifices (which were pretty small).

Gary has done some great work on integrated designs, and I'd love to see more tin bent to prove (or find and work out the problems with) the concepts. (Gary strikes me as something of the Preston Tucker of the space transportation biz.)

Re:Gary Hudson

[Anonymous Coward]

I'm sorry, but the idea of beer-assisted entry is actually an ancient Bavarian idea and it clearly predates Gary Hudson.

Liquid nitrogen?

[girlintraining]

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:Liquid nitrogen?

[Anonymous Coward]

You are right, we should not do anything at all ever! This is the only way to ensure that nothing ever goes wrong!

Re:Liquid nitrogen?

[h4rr4r]

Nothing worse than what happens when the stupid shuttle on the side design leads to the shuttle's tiles being broken.

I agree there is risk, but it can't be worse than the shuttle.

Re:Liquid nitrogen?

[sub67]

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:Liquid nitrogen?

[Delarth799]

And if we never bothered to take chances with new/advancing technology where would we be today?

Re:Liquid nitrogen?

[tsotha]

It's pretty normal for rocket engines to be regeneratively cooled with explosive fuel. This kind of approach has its flaws, but you haven't identified one of them. For a space ship during reentry every point on the airframe is critical.

Re:Liquid nitrogen?

[drayath]

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:Liquid nitrogen?

[wagnerrp]

If such cooling systems were prone to failure, we would have airliners regularly falling out of the sky. Jet engines use this same exact technique to protect their combustors and turbines. Were the film to fail, you would have maybe 30 seconds before that whole section of the engine completely melted away.

Re:Liquid nitrogen?

[Anonymous Coward]

The X-15 used this method successfully at Mach 6.

Re:Liquid nitrogen?

[Anonymous Coward]

Not only that, but where on Earth will they get all that nitrogen? It's not like the stuff is just pooling up in underground caverns. The wastefulness just takes my breath away.

Re:Liquid nitrogen?

[uvajed_ekil]

Yeah, it sounds like a useful technology, very interesting... until one of the numerous components in the system fails. Too many potential failure points for such a critical system. Will the tiles be effective if the gas system goes non-op?

Re:Liquid nitrogen?

[alba7]

In general, air consists of molecular Nitrogen (N2) with a volume count of 78%. To extract it you just need to cool the air until the Nitrogen liquefies. This process was discovered in the 19th century and is the base of inorganic chemistry.

Re:Liquid nitrogen?

[trout007]

I was talking to one of the engineers that developed this system to replace the leading edges of the shuttle. It is similar to what the Germans are doing but it uses heat pipes to carry the heat from the most intense heating areas to relatively cooler ares. It worked like a champ but one of the problems with the Space Shuttle Program is that is was treated like it only had 5 years left for the last 20 years. If instead we kept upgrading them and fixing the high cost items we might have something that is a lot cheaper to operate. This report is from 1998. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.30.3183&rep=rep1&type=pdf

USA USA...oh wait GERMANY GERMANY

[Anonymous Coward]

lol

Weight

[galvitron]

I would think that the big concern with a system like this is the added weight. Is it more cost-effective to have an active cooling system such as this, but carry along the plumbing, tanks, etc.? Or is it better to simply have replaceable tiles like the shuttle, and save the weight...then have to perform all of the required maintenance to the leading edges before the next flight?

Re:Weight

[tsotha]

The problem with the shuttle program was really all the things that had to be done between flights. It was originally supposed to have a two week turnaround, something that turned out to be a pipe dream because of all the things that needed to be inspected and refurbished. If the Germans can make a ship that needs less inspection and maintenance, they can fly it more often. That will bring down the $/kg-to-orbit cost, which I think ought to be the goal of any serious space program at this point.

I've thought of that myself

[istartedi]

I've thought of active cooling myself. I always wondered, if you used an active cooling system, where would you radiate the heat? In other words, you can carry heat away from the underside of the ship by pumping a fluid through the tiles or whatever, but then you still have to re-radiate that heat someplace. OK, you might be able to transform some of the heat into useful work too; but we're talking about a lot of heat, and even if you got right to the Carnot efficiency the waste still has to go someplace.

I never got as far as doing the "back of the envelope" calculations on some substance with a heat capacity to absorb re-entry heat (and light enough to carry onboard) or the more tricky calculation of how you would conduct the heat from the underside and radiate it topside. I kind of assumed that actual aerospace engineers had done the calcs, and decided it just wouldn't work.

Weight kills in space, so I'd be curious to know how much the system weighs vs tiles or Russian-style ablative coatings. I'm assuming the Russians still use ablatives. I'm sure somebody will correct me if I'm wrong.

Re:I've thought of that myself

[aquila.solo]

...but then you still have to re-radiate that heat someplace.

The way I read TFA is that the N2 coolant is consumable. Rather than circulating it to a heatsink, they just expel it through pores in the surface, allowing the gas to buffer the compressed air during reentry. It brings cooling back into a convective mode.

Sure you have to refill the tanks prior to the next launch, but liquid nitrogen is (relatively) cheap.

Re:I've thought of that myself

[sznupi]

If only it just meant refilling the tanks; I worry more about limiting the time of storage in orbit.

Re:I've thought of that myself

[Rei]

I've thought of active cooling myself.

I think pretty much everyone who's lived in Houston in July has as well. ;)

I always wondered, if you used an active cooling system, where would you radiate the heat?

You vent the heated gas. Aka, it's a gasseous ablative.

Re:I've thought of that myself

[wagnerrp]

You're thinking about this completely the wrong way. This is not actually cooling at all. They are injecting cold gas into the flow, against a positive pressure gradient. The pressure keeps the flow pressed against the surface of the craft, producing a protective film. The film prevents the craft from ever heating up in the first place. While this is a novel use of the technology, the technology itself is nothing new. It has been used for decades in rocket nozzles and gas turbines to protect the hot sections, and is a well understood and researched technique.

Re:I've thought of that myself

[tsotha]

You also have to carry all that nitrogen from the moment of launch all the way through reentry. Scrapping the wings and making a powered landing might have all the advantages of this scheme without having the complication of the nitrogen "pores".

Re:I've thought of that myself

[Crypto Gnome]

Use the heat to generate electricity (stirling engine/thermopile/?)

Use the electricity to generate a charge on the outside of the vehicle

Excessive heat generates a plasma in the atmosphere on the leading edge

Plasma is repulsed by the external charge.

?? Surely that leads to at least a non-trivial amount of heat being avoided?

Re:I've thought of that myself

[Crypto Gnome]

Of course, if real world science was as good as comics and speculative fiction have left us dreaming of , re-entry vehicles would be cooled by

1. Heat-Pump Lasers
   
   or perhaps
2. Cryptoanalysis*

Seriously folks, scientifically speaking it takes *energy* to "do work", so for any given method of converting heat-energy into "work", if you give the problem enough *work* to do, it should pretty much initiate the next ice-age were said experiment to be conducted on a planetary surface.

Of course, todays heat (as input) to work (as output) conversion technologies are , sadly, inadequate/inefficient and generally distinguishable-from-magic. However, having said that... that (efficiency) is only a problem in *engineering*.

Re:I've thought of that myself

[istartedi]

You also have to carry all that nitrogen from the moment of launch all the way through reentry.

This is the *weight* issue I touched upon. What I should have said was, "in space, weight is money". Every kg of non-payload you have to carry is something that could have been payload. Here are some ballpark figures for orbiting on a per-kilogram basis.

Don't get me wrong; it sounds like an interesting research project. Who knows, there might be some point in the future where this technology offers the best approach. That's why you do basic research. Don't get me right either. Somebody still has to count the beans. Heheh... don't get me wrong, and don't get me right. I like that...

Re:I've thought of that myself

[quanticle]

In essence, the nitrogen pumped through the pores of the ceramic forms an "ablative" coating, as it absorbs and carries heat away from the surface of the craft. The nitrogen has to be refilled after every launch, but refilling a nitrogen tank is cheaper and easier than reapplying an ablative coating or repairing ceramic tiles.

Re:I've thought of that myself

[camperdave]

Scrapping the wings and making a powered landing might have all the advantages of this scheme without having the complication of the nitrogen "pores".

So instead of carrying nitrogen, and letting atmospheric effects slow you down, you want to carry as much fuel as you took to get into orbit with you so you can get back down?

Re:I've thought of that myself

[tsotha]

Nah, it's not that much. Not even close, since your spaceship weighs only a fraction of GLOW on reentry. Somewhere between a fifth and a tenth of GLOW. And dumping the wings is a considerable weight-saver, so it's not clear that those atmospheric effects are really buying you anything.

Re:I've thought of that myself

[maxwell demon]

Efficiency of converting heat into work is not just a problem of engineering. There's a fundamental limit due to the second law of thermodynamics. You simply cannot extract heat from the surrounding and convert it into work. You always need a heat sink, and you always will lose some of the heat to the heat sink. The maximal theoretical efficiency you can get depends on the temperature difference between heat source and heat sink, but is always less than 100%.

Re:I've thought of that myself

[camperdave]

so it's not clear that those atmospheric effects are really buying you anything.

The atmospheric effects are buying you a safe trip to the ground. The atmospheric effects are what sheds all of that orbital speed. If you want to come down using a powered descent, then you're going to need to put as much energy into slowing the capsule as you put into getting it up to orbital speed in the first place. It is not a trivial amount of fuel, I would guess far more mass than a pair of wings and the cooling nitrogen.

Wings increase the capsule's surface area, which brings the capsule's speed down faster. Wings also give you final approach control, allowing you to touch down on a runway rather than splashing down in the ocean (requiring a massive naval search and rescue operation).

Having said that, I think an inflatable heat shield and a parafoil would be the best solution.

Re:I've thought of that myself

[pipingguy]

That's the way I read it too. And yes, N2 is cheap.

Thank God it's unmanned

[Locke2005]

Mixing liquid nitrogen and 10,000 degree re-entry friction temperatures... no thermal stress there! There is a reason why your father told you to never throw hot water onto your icy windshield to defrost it -- this sounds like the converse, throwing really cold liquid into a hot tile. Unless the tile has a thermal coefficient of expansion of zero, I'm betting this will crack some tiles.

Re:Thank God it's unmanned

[wagnerrp]

This technique doesn't cool anything, it prevents the tile from ever heating up in the first place. It has been in use for decades in gas turbines and rocket nozzles. http://en.wikipedia.org/wiki/Turbine_blade#Cooling

Re:Thank God it's unmanned

[dwywit]

Uh, perhaps they'll start before the tiles get that hot? i.e. before it even starts to heat up, so that it never gets that hot?

Re:Thank God it's unmanned

[h4rr4r]

I am glad we have you to make these observations, I am sure the scientist and engineers working on this project have not thought about such issues. I urge you to email them right away with your insight into their project.

Re:Thank God it's unmanned

[Anonymous Coward]

and the idea itself is not new either - I've references from the early 60s that had so-called transpiration cooling designs, and helium (and possibly other gaseous coolants) were mentioned.

Think of it as ablative cooling by outgassing

[SixAndFiftyThree]

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:Think of it as ablative cooling by outgassing

[Rei]

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:Think of it as ablative cooling by outgassing

[wagnerrp]

The nitrogen gas is not used as a heatsink, it is used to produce a protective film against the surface of the reentry craft. The film prevents the high temperature plasma from touching the craft, and is much more effective at keeping the craft cool then simply using it as a mechanism to dump the heat overboard.

Re:Think of it as ablative cooling by outgassing

[DerekLyons]

inspecting and replacing ablated ceramic is one of the reasons why the Shuttle takes months to turn around

While damaged or loose tiles are replaced - there is no such thing as an 'ablated' tile on the Shuttle.
 

Replacing the ablated nitrogen is as simply as putting a hose in the tank after the craft lands

That's true - but only half (or less) of the story as there is more to the system than than just the nitrogen. You also have to consider maintenance on the valves and piping (which the shuttle does not require) and you'll also require detailed inspection/repair/replacement of the heat shield components (just like the Shuttle).
 
So after figuring in the need for the shield to be able to operate sans nitrogen (in the event of a failure in the valve system), the bulky and heavy tanks and piping, the bulky and heavy LN2 itself, the specialized 'porous' heat shield, etc... etc... it's not at all clear this will end up cheaper and lighter than the Shuttle, let alone whether a practical craft can be built.

Re:Think of it as ablative cooling by outgassing

[pipingguy]

I was under the impression that there was a fair amount of complex piping involved in the shuttles. How about the N2 is stored as liquid air doing double duty as O2 source and re-entry shield gas?

Re:Think of it as ablative cooling by outgassing

[DerekLyons]

I was under the impression that there was a fair amount of complex piping involved in the shuttles.

There is - but for cooling, hydraulics, etc... not heat shielding. And any Shuttle type replacement will require the same piping systems.
 
So what I'm doing here is comparing like-to-like, the Shuttle's heat shielding system to this test vehicles heat shielding system.
 

How about the N2 is stored as liquid air doing double duty as O2 source and re-entry shield gas?

You'll note I specified LN2 - liquid nitrogen. You'll also note that N2 != O2.

Re:Nice to see

[aix tom]

The V-2 already had her share of makeovers. For example the Redstone or the Canadian Arrow

a more aerodynamic solution?

[funkboy]

Being somewhat of a firearms geek, I've been reading up a lot on ballistics lately.

Rather than using airplane-like control surfaces & gliding wings that are basically dead weight until it comes time to use them as a huge airbrake & then as wings for an airplane-like landing after re-entry, what would be the feasibility of a vehicle shaped like a bullet with an extremely low coefficient of drag that would re-enter gradually through a series of ever-lower orbits through the upper atmosphere until it slowed down enough to open a parachute (or a series of parachutes gradually increasing in drag)? Incidentally, the low CD would also enable it to maintain LEO with fewer orbit maintenance burns as there would be less drag on it from the upper atmosphere (see also the ISS...).

Has anything like that been tried before? Is such a trajectory even possible? Is that what the space shuttle does already, and the stall speed is so high that it has to conventionally re-enter anyway?

Some doodling shows that the trick to this would be to optimize the design of the vehicle to be able to "fly" at a trajectory that would trade speed for altitude until it stalls & drops like a stone, at which point the parachutes take over. Basically, it would be shaped to shed its orbital velocity by "surfing" on the top of the atmosphere until it "sinks".

Re:a more aerodynamic solution?

[Anonymous Coward]

First, I'm having a bad day today and I no longer work for a space program. So take this with a grain of salt.

You have two main issues:

1) Dynamic stability

How do you keep it going in this trajectory once in the atmosphere? It will roll along it's longest axis and after that drift to the rolling side.

2) Heat

Re:a more aerodynamic solution?

[wagnerrp]

Aerobreaking and aerocapture have been used on several occasions as a mechanism for altering or entering orbit using a reduced amount of fuel. The version you are referring to is specifically called a 'skip renetry' and has been used on a handful of Russian orbital missions. http://en.wikipedia.org/wiki/Skip_reentry

Re:a more aerodynamic solution?

[rts008]

Being somewhat of a firearms geek, I've been reading up a lot on ballistics lately.

Ditto, but I started out Benchrest shooting in the latter 1960's. :-)
I shot at Camp Perry[1] twice as a qualified competitor.

*Disclaimer: I am not a rocket scientist, but know quite a bit about basic physics, and ballistics in particular.*

How do you propose to shed heat on those continuous, progressively intense, cumulative orbits?

Maybe a rocket scientist could explain it better than I, but this is a fundamental consideration(atmospheric drag/friction) in calculating the ballistic coefficient for projectiles.

[1]
Camp Perry is an elite club.

Re:a more aerodynamic solution?

[funkboy]

Thanks :-). Any idea what the highest number of "re-entry skips" that's been attempted is?

Hot plasma?

[jasno]

Isn't the hot air around the returning vehicle a plasma? If it is, can you repel it with proper use of electromagnetism?

Re:Hot plasma?

[FleaPlus]

Isn't the hot air around the returning vehicle a plasma? If it is, can you repel it with proper use of electromagnetism?

Jon Goff, an aerospace engineer whose blog you should probably read in general because it's awesome and chock full of great aerospace analysis/ideas, had a rather intriguing discussion a few months ago about doing pretty much what you describe, applying magnetohydrodynamics to the problem of thermal protection during atmospheric reentry:

http://selenianboondocks.com/category/mhd-aerobraking-and-tps/

(Jon Goff's an engineer with Masten Space Systems, the company that won the most recent Lunar Lander Challenge)

Disposable sheilding

[DigiShaman]

Here's an idea. Why not use material good for one re-entry, then shed it to lighten the load? Perhaps an overlapping plate formation might work.

Re:Disposable sheilding

[Jesus_666]

Now where did I hear about that technique...?

Can I ask a question of someone smarter than me?

[Anonymous Coward]

Something about re-entry has always troubled me and I'm hoping someone more familiar with the physics can answer it.

A spacecraft traveling at 18000MPH is in orbit then slams into the atmosphere, creating ram pressure that heats up the craft until it slows to a more acceptable atmospheric speed. The question is: why bother?

Couldn't a craft simply slow itself to a much more reasonable speed before re-entering the atmosphere with a thruster braking mechanism or some such? Is it just an issue of the fuel weight being used for braking? Wouldn't the safety mechanisms, heat resistant tiling, etc. come out as even heavier than simply allocating more fuel for braking?

Reminds me of Russian torpedos

[Anonymous Coward]

The Russian torpedo goes ~200MPH through water by enveloping itself in gas. If this nitrogen envelope reduce drag how does one bleed off of speed?

How about a "sprayable" ablative coating

[Anonymous Coward]

Hey NASA guys how about we develop a spray on ablative coating? (imagine sprayfoam but less flamable)

Heatsink Technology

[Anonymous Coward]

I knew all that Pentium 4 heatsink technology would scale someday!

It feels better to laugh than to cry....

[rts008]

I urge you to email them right away...

Don't stop there!!!
Twit your twat...tweet on twitter!!! I think I saw a putty cat!
Write your congressman and senator, but include lots of pictures, graphs, and diagrams. Most of them are, uhmm, 'reading challenged'. Yeah, that's it.
Start a facebook group!
Take over the world! The solar system! The galaxy!
The possibilities are endless!®©$$

Some one else thought of it and built it.

[trout007]

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.30.3183&rep=rep1&type=pdf

Re:Can I ask a question of someone smarter than me

[trout007]

You are correct. If you had enough fuel you could brake the craft to a much lower speed.Think about all the fuel needed to tiny payload from the surface of the earth to orbit. You would need the same amount if you wanted to make a tail first landing back on the launch pad. Think of space ship one. It falls from space about 60 miles but with no tangential velocity. It makes it back with regular composites.

Re:Can I ask a question of someone smarter than me

[maxwell demon]

Ever looked at the rockets used for lift-off? They are made mostly of fuel. Most of it is needed just for not falling (i.e. accelerating) down. In other words, it would be needed for going downwards slowly as well.

Unless you can land it on a runway who cares?

[trout007]

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? Seems like you will be picking salt and sand out of it for a long time. I've seen many Space Shuttle Landing in person and we are going to miss the ability to land a couple of miles away from the hangar.

Re:Unless you can land it on a runway who cares?

[FleaPlus]

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.

Re:Unless you can land it on a runway who cares?

[turgid]

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.

Imagine surviving launch atop a flaming stack of high explosives, the radiation of space and the hazards of re-entry to be dropped and splattered on the ground by a butter-fingered helicopter pilot.

Re:German technology in Apollo/Saturn

[Suzuran]

Germans made the booster, but we made the rest.

The Saturn was Von Braun's design. The LVDC program that guided the Saturn was a port of a FORTRAN program that implemented a set of control laws and arithmetic written by the Germans. The rest of the program was mostly US design. The Germans had relatively little to do with the CSM and LM. Their job was to get things into space and to a lesser extent down again, but dealing with it once it was in space was beyond their original research. We paid for the entirety of their work in those areas (life support, stellar navigation, long-distance communications, etc) while they were living here and holding American citizenship, so at that point they were more German-born Americans than Germans.

There were also more than a few Germans performing various operational roles. Gunter Wendt, for example. Their contribution should not be discounted either, but it's hard to quantify.

Shrouded Tuyere

[pipingguy]

That reminded me of another application of nitrogen as a shielding gas in high temperature environments, the shrouded tuyere in copper/nickel converters.

Hot Shit?

[Anonymous Coward]

Bah, transpiration cooling has been proposed and in some cases tested/fielded.

Call me when the superconducting magnetic field reentry shield where the mag field pushes the reentry plasma away from the spacecraft has a flight demo.