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Reaction Engines To Fly Reusable Spaceplane

Posted by timothy on from the let's-just-start-here-on-the-ground dept.

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."

5 of 156 comments (clear)

  1. enough propellant? by khallow · · Score: 4, Interesting

    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.

    1. Re:enough propellant? by evanbd · · Score: 4, Interesting

      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.)

    2. Re:enough propellant? by StevePole · · Score: 5, Interesting

      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)."

      More info here: http://www.reactionengines.co.uk/sabre.html

      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.

  2. Re:Space Elevator by evanbd · · Score: 5, Interesting

    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.

  3. Re:Space Elevator by evanbd · · Score: 4, Interesting

    Actually, if you want a mega-scale engineering project, my personal preference is for the launch loop.