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## Reaction Engines To Fly Reusable Spaceplane156

RobGoldsmith writes "Reaction Engines have designed a 'reusable spaceplane' to provide inexpensive and reliable access to space. The Star Wars-looking 'Skylon' reusable spaceplane has already been designed and the team are well into engine testing. They have taken some time out from building spaceships to talk about their background, their goals, and their recent engine tests. This article shows new images of their STERN Engine, an experimental rocket motor which explores the flow in Expansion Deflection (ED) nozzles. They also discuss their Sabre air-breathing engine technology. View the Skylon Spaceplane concept, the STERN Engine and much more in this in-depth interview with the team."
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## Reaction Engines To Fly Reusable Spaceplane

• #### Dollars per kg? (Score:2, Interesting)

on Monday January 12, 2009 @01:52AM (#26413779) Journal
Can anyone find a cost per kg (or lb) of cargo estimate on that website? Not trying to detract from its value, just wanted it for comparative purposes.
• #### enough propellant? (Score:5, Interesting)

on Monday January 12, 2009 @03:02AM (#26414143)

It doesn't seem to have enough propellant mass for the task. To get to LEO, it needs something like 7.5 km/s or more in delta v (ignoring very substantial gravity and air resistance losses). If it were purely a rocket, that would be roughly 7.2 km/s (rocket equation is delta v = -4420 m/s*log(53 tons/273 tons), where 4420 m/s is perfect exhaust velocity in vacuum for LOX/LH2 burning rockets). Even if we assume we can get to Mach 5 for free (which is 1.5 km/s roughly), that leaves no more than 1.2 km/s margin. A regular rocket picks up 1.5-2 km/s or so in gravity and air resistance losses. While gravity losses might be somewhat lower (due to lift), air resistance is definitely going to be higher than the 100-200 m/s a rocket of similar size would have. So we have gravity and air resistance losses. We also have probably an inefficient nozzle design with a tradeoff between greater bell size (and efficiency in vacuum) and lower air drag. Something like drop tanks would help a little, but there doesn't seem to be the space for a lot of extra mass there. Another possibility is to use denser fuel in place of LH2 for the early parts of the flight, but that weakens the isp a little.

• #### Re:Space Elevator (Score:5, Interesting)

on Monday January 12, 2009 @03:03AM (#26414147)

I don't much like the idea of a space elevator, at least for short- or medium-term applications. (Long term, is 50 years from now, is different... but also not very relevant.) Why, you ask? Simple. Give me a space-elevator class building material, and I'll make rocket tankage out of it long before it's fully developed to space elevator performance levels. Those tanks will be so vastly superior in weight performance to current materials that I can give you a rocket that is not only single stage to orbit, but does it on *pressure fed* engines. Who needs turbopumps and all their associated machinery when you can just put enough pressure in the tanks (and run at a lower chamber pressure... which is more conducive to high reliability anyway)?

For a given payload rate, my pressure fed SSTO will use somewhere between 3 and 10 times the energy (depending on which kool-aid you drink when it comes to getting the power from the ground to the elevator car). It will have a *vastly* lower capital cost. It will be faster (no radiation worries for cargo that spends days passing through the van Allen belts). Perhaps more importantly, it will scale down better. It starts with a lower investment and lower flight rate to prove out demand, and then grows as more customers appear and more rockets get built.

Oh, reusability? It gets a lot easier when you don't have to jettison a stage a third of the way there -- and when your reentry vehicle is as light and fluffy as these building materials imply, it gets even easier. Engine reusability is pretty trivial when you don't have 60,000 rpm turbines wearing out all the time.

There are plenty of engineering problems to be overcome for a space elevator. They're not impossible, but they're far from trivial. But the real problem is the competition from rockets -- it makes zero sense to compare a space elevator built with magic nanotubes to a lithium-aluminum tankage rocket; it should be compared to a magic nanotube rocket. When you do that, you discover that for any unproven market (ie, where capital costs matter) the spaceship fleet is far, far cheaper.

• #### Re:enough propellant? (Score:5, Interesting)

on Monday January 12, 2009 @03:27AM (#26414231)

You can get slightly better Isp than that, actually. For example, I get 4664 m/s vacuum Isp for O:F of 6:1 and 3000 psi expanded to 1 psi. I don't know what pressure they run at, but for a wide altitude range I would imagine it's high. Furthermore, I believe they plan to still be using some outside air even at Mach 5 -- and at that altitude, they've also got some delta-v in the altitude itself, not just the velocity. Small effects, but they help... Anyway, I don't know the details of their flight plan, but I do know that the engineers behind it are decidedly competent, and do have a detailed trajectory plan that includes good estimates of air drag and such. If you can find trajectory details, though, I'd love to see them...

(Oh, to pick a few nits about your dv budget... 7.2 km/s is orbital velocity; don't forget nearly 500 m/s of Earth rotational velocity. So if you ignore air and gravity drag, it's actually slightly under 7 km/s total delta-v, though air and gravity drag will usually add more than 2 km/s to that.)

• #### Re:Space Elevator (Score:3, Interesting)

on Monday January 12, 2009 @03:31AM (#26414247)

Sure, but guess what? I bet even current launch vehicles can do a lot better in cost per kg than they currently do. I figure the limit of expendable launch vehicles are somewhere around \$500 per kg in very high launch volume (thousands of launches a year). RLV would drive that to somewhere around \$100 per kg. At that point, you have the business to justify that next step to exotic technologies like space elevators, rail launch, etc. This is the point that I think is being missed. There's little reason to fund a lot of space elevator research now. And by the time there is enough reason, it pays for itself.

• #### does this add up ? (Score:4, Interesting)

on Monday January 12, 2009 @03:40AM (#26414287)
from this presentation [space.co.uk]:
- air intake in the order of hundreds of kg per second (400 kg/s to quote) ...
- passes through thousands of small tubes (resistance at that speed ?!?) ...
- in a few milliseconds ...
- cooled from + 1000degreesC to -150degreesC

Forgive me my ignorance, but are these materials physically possible ?
• #### Re:Space Elevator (Score:4, Interesting)

on Monday January 12, 2009 @04:00AM (#26414365)

Look into the Space Fountain instead... http://en.wikipedia.org/wiki/Space_fountain [wikipedia.org]

• #### Re:Dollars per kg? (Score:3, Interesting)

on Monday January 12, 2009 @05:11AM (#26414639)

Yes, lot of stuff needs to be added. At a glance, it looks like they can use a convention runway (though it might need to be reinforced, apparently a loaded vehicle generates a lot of impact on landing). Insurance isn't much of a cost for the launch provider. Insurance against third party harm is rather low since US launch providers need to demonstrate a ridiculously low risk of harm before they can launch anyway. Insurance for the payload should be pretty good for an RLV with the kind of launch frequency this will need. Fuel costs are pretty low. Probably going to be something like \$20-50 per kg of payload depending what they get the LH2 for, I think.

Maintenance could be a hidden problem. I think the DC-X, an unmanned prototype (for SSTO eventually) had composite tanks. There were serious problems with thermal flexing and penetration by cryogenic fluids that weakened the tanks. If I recall the blurb for the Reaction vehicle, it would use aluminum lined tanks, which addresses most of that problem.

• #### a 21st Century DC-3 (Score:3, Interesting)

<alizard.ecis@com> on Monday January 12, 2009 @05:15AM (#26414665) Homepage
From what I saw at the company website, it looks like they're building the orbital equivalent of the first commercial airliner, the DC-3.

If they can get the cost to orbit even remotely close to the \$200/kg number the Space Power Satellite program proposed by NASA was based on, we could either build a full system or a large proof of concept orbital power array. We're a bit more desperate for power than we were when Bush defunded the SPS project. The launch capability is the hard part of SPS, the rest is just engineering we know how to do.

That could take up enough launches to provide the company a reasonable chance at profit.
• #### Re:enough propellant? (Score:5, Interesting)

on Monday January 12, 2009 @06:12AM (#26414893)

A friend of mine works on the heat exchange system for the SABRE engines that will power Skylon. The SABRE engines are air breathing i.e. they use air they pick up on the way as fuel, hence they need less fuel at launch.

From their website: "The Sabre engine is essentially a closed cycle rocket engine with an additional precooled turbo-compressor to provide a high pressure air supply to the combustion chamber. This allows operation from zero forward speed on the runway and up to Mach 5.5 in air breathing mode during ascent. As the air density falls with altitude the engine eventually switches to a pure rocket propelling Skylon to orbital velocity (around Mach 25)."

The engine saves weight by using the same combustion chamber during both modes of operation and in air breathing mode it only cools the oxygen to it's vapour point (as opposed to full liquidization) which greatly simplifies the engine design.

At least that's my understanding, IANARS.

• #### Re:Space Elevator (Score:5, Interesting)

on Monday January 12, 2009 @06:50AM (#26415029)
Actually, if you want a mega-scale engineering project, my personal preference is for the launch loop [wikipedia.org].
• #### I see... (Score:1, Interesting)

on Monday January 12, 2009 @07:41AM (#26415207) Journal

... 5 million pounds spent in developing an engine.
I see tests that have demonstrated only the precooler - not the thrust, not the reliability, ie none of the things critical to it actually working.

I see no prototype having been tested.

I see something that's a hairsbreadth from the 'I've pulled this kewl idea out of my butt!'.

• #### Re:a 21st Century DC-3 (Score:2, Interesting)

on Monday January 12, 2009 @08:43AM (#26415519) Homepage

From what I saw at the company website, it looks like they're building the orbital equivalent of the first commercial airliner, the DC-3.

Bit of a nitpick here, but that would be the first tremendously successful commercial airliner.

The DC-3 was an evolution of the DC-2, which was designed to compete with Boeing's 247. The 247 itself was preceded by a bunch earlier designs by various constructors, like the Ford Tri-Motor.

• #### Re:enough propellant? (Score:3, Interesting)

on Monday January 12, 2009 @11:45AM (#26417591)

Yes, that's pretty much what I gathered from looking at the design, especially the odd-shaped, untapered outlets for the Sabre engines and the fact no other nozzles appear anywhere on the ship.

The engine saves weight by using the same combustion chamber during both modes of operation and in air breathing mode it only cools the oxygen to it's vapour point (as opposed to full liquidization) which greatly simplifies the engine design.

This sounds like quite an effort. Would like to see if it works out. Recently, I was discussing a scramjet design [nasaspaceflight.com] with the internet:

tnphysics: The key to a gas-and-go SSTO RLV IMO is airbreathing engines-somewhat like the Forerunner V business jet proposed somewhere on the forum (afterburning ultra-high-bypass turbofan to Mach 8, then LNG scramjet to Mach 15, then switch to LH2 to Mach 20), with a small rocket added for EOI. A metallic TPS should be used.

At the time, I recommended reducing the complexity of the vehicle by eliminating the air-breathing turbofan at the start and using the rocket instead to get the vehicle up to scramjet speeds. The Sabre engine sounds like a more effective way to do that. It could boost the vehicle up to Mach 8 with a combination of air breathing and rocket modes, switch over to the scramjet for that phase of the acceleration, and then switch back to the sabres for the final acceleration to orbit in vacuum. Still overly complex, but the Sabre is a good fit for the launch profile.

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