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British Spaceplane Skylon Could Revolutionize Space Travel (ieee.org)
MarkWhittington writes: The problem of lowering the cost of sending people and cargo into low Earth orbit has vexed engineers since the dawn of the space age. Currently, the only way to go into space is on top of multistage rockets which toss off pieces of themselves as they ascend higher into the heavens. The Conversation touted a British project, called Skylon, which many believe will help to address the problem of costly space travel. According to IEEE Spectrum, both BAE Systems and the British government have infused Skylon with $120 million in investment.
Skylon's idea is to use oxygen from the air, rather than taking the oxygen as fuel for the initial part of the ascent. A well known idea that is being worked on elsewhere.
Ultimately jet engines are just complex rocket engines that use outside air for the oxidizer. The reason commercial jet engines are more reliable, generally, is they aren't pushed to the very edge of what's possible, performance-wise, and they're produced in large quantities. But neither will be true for the Skylon SABRE engines. I don't see any reason to think they'll be any cheaper to maintain than the Space Shuttle Main Engines.
I've sometimes pondered the concept of a self-consuming rocket engine - basically infinite-staging.
Picture a spike (although the ideal shape would be different from an aerospike) comprised of small channels between aluminum - for example, assembled via fine aluminum wires or finely corrugated aluminum sheets, all the way through, thus leaving empty space between them. The wires or sheets would be joined together by having any surface oxide removed (or inhibited altogether by alloying agents), and heated enough in a non-oxidizing environment to braze them together. The channels would be filled with an oxidizer-rich polymer/ammonium perchlorate mixture (very mainstream as far as propellants go).
The engine would need to be lit off across its entire surface, so all channels ignite (or be designed such that neighboring channels ignite neighbors who fail to ignite).
The propellant mixture would burn down into the channels (as even fine aluminum wire/sheeting takes time to burn through) - lacking any area within the channels to expand into, it remains compressed and accelerates linearly as it moves through the channel (design parameters set such that the compression ratio achieved is the desired compression ratio for the engine). The angle of the channels would direct the stream largely along the spike, so that the gases expand along an ideal expansion profile for generating forward thrust. Since the entire spike would be comprised of channels, again, the ideal shape would be different form an aerospike; the exhaust gases don't simply come from the top.
As the oxidizer-rich propellant burns down, it progressively erodes the aluminum making up its channels (again, alloying agents in the aluminum may be used to help or hinder this process). Since the exterior ends of the channels would be exposed to the oxidizer-rich exhaust for the longest, they'd progressively burn down from their ends. Since the exhaust burns further as it flows (and the oxidizer would be more liberated), again the erosive potential of the stream would be highest near the end of the channels. So like a wick keeping pace with a candle as it burns down, the channels would be expected to erode away at approximately the same rate that the propellant burns down.
Aluminum metal is itself is a very energetic-burning compound - aluminum dust is often included in solid rocket mixes, so the erosion of the aluminum channels is a significant thrust contributor. Lithium-aluminum would be even better - lithium-aluminum is stronger than aluminum, and lithium is even more energetic than aluminum. It would also help neutralize the hydrochloric acid that occurs in most ammonium perchlorate-based solid propellants (although there are other techniques as well, such as burning magnesium and/or sodium nitrate with it).
In a naive implementation, the spike would change from the ideal shape to a progressively suboptimal shape as it burned down. But the rate of propellant burn and aluminum erosion could be controlled by tweaking the parameters of the system such that the areas of the spike you want to last longer can burn down slower than the areas you want to burn down faster. Hence the ideal spike shape can be retained as the engine burns down, all the way to right before it burns out.
Basically, your rocket would be... no rocket at all; just propellant. The entire thing is consumed. It'd be useless for orbital maneuvering**, but to get to orbit, the rocket equation likes nothing better than non-stop continuous staging with no tankage or engine mass at all (a caveat in this regard: your gimbaling system and interstage would still have to be sized for when it's at full size and max thrust). No complex systems at all. No exotic manufacturing techniques needed. No exotic, expensive materials. Just aluminum and a not-particularly-unusual solid rocket propellant. Getting the details of the mix right to ensure 1) even ignition, 2) even burndown, and 3) aluminum erosion at the proper rate would take research and experimentation, but I would e
The yellowcake is a lie.
If I remember correctly, Reaction Engines got severely dicked by the UK government (pulling funding declaring the engines covered by the Official Secrets Act), effectively ending private development.
The design was promising but had teething issues, and has been carried on as a garage project all these years.
That they've managed to get this far given the hurdles they've had to overcome is nothing short of astounding.
I have followed Skylon for several years now. The engines are very interesting, in fact, the whole design, including the wings is very cool. The wings take the gravity load off, which for something that takes that long to get to orbit is quite an advantage.
They actually get more energy out of the hydrogen than they would get from just burning it. The reason is that they run the compressor on the temperature difference between ram air and the LH2 flowing to the engines. Burning hydrogen gives about 50 kWh/kg, it takes 20 kWh/kg to make it into a liquid.
You might note that everyone who has been given the full inside information, including the USAF, agrees that it will work as a SSTO. If anyone wants to build power satellites, Skylon is the only thing that is likely to get the cost to where power satellites could undercut coal.
End MGM. Get prospective parents of boys to Google: Men do complain