Addendum on Jet Propulsion Technology

10 July 2012


In yesterday’s post on China’s Military Aviation Ambitions I discussed some of the early difficulties in jet propulsion, and how the most advanced jet engines of our time continue to be a technical and engineering challenge. China, as I mentioned, buys its most advanced jet engines from Russia and the Ukraine, who apparently possess industrial plant tooling and technical expertise superior to what the Chinese are currently capable of matching.

I expect that this technological hurdle will continue for some time, since despite the fact that jet propulsion technology is older that the technology of nuclear weapons (which I have elsewhere called a mature technology), there is still a great deal of technological and engineering work to go on jet propulsion.

In the past few decades jet propulsion technological research has focused on higher efficiencies, and this research has resulted in passenger jet service that uses significantly less fuel than the first Jet Age when, in the 1960s, passengers jets first began to routinely offer international travel. But I have also noted that the then-expected transition to supersonic jet travel didn’t happen; supersonic jets were loud and expensive and used a lot of fuel. The time saved by supersonic travel was not at that time, and has not up to this time, been enough to offset the disproportionate costs of supersonic passenger travel (although supersonic military jets are now entirely routine, with the newest fighter jets possessing supercruise ability).

But that isn’t the only thing that slowed down the advent of the age of supersonic jet travel. Supersonic jets are a difficult technology to master, and require substantial engineering and technological resources. We still have a long way to go (and therefore many opportunities yet in the future — even the near future) in terms of routine and cost-effective supersonic travel. Since supersonic jet travel has been stalled for some time, it is beginning to feel like fusion power — an engineering challenge just beyond our current reach — always another thirty years in the future.

On my other blog I wrote about tests this past spring on the essential systems of the REL SABRE engine (Synergetic Air-Breathing Rocket Engine — an illustration of which is pictured above), which is of the greatest interest for future jet propulsion technologies. This is an engine that can take us into space, and is therefore the future and an important technological milestone. The SABRE engine (you can see an animation of its operation both on the REL website and at Vimeo) is designed for SSTO (Single Stage To Orbit) and HOTOL (HOrizontal Take Off and Landing) operation — in other words, this is the engine for the kind of spaceships that you see in the movies, that take off from the ground under their own power, like an airplane, and are able to keep accelerating all the way through the atmosphere and then into space.

Maybe I sound like a booster for REL — their website calls the SABRE engine, “a major breakthrough in propulsion worldwide” — but it would be difficult to underestimate the importance of this propulsion technology, not just for the business of space launch, and not just for any particular industry, but for the human species. If we stay on the earth, we are doomed; we will only propagate our civilization if we become a spacefaring civilization, and an SSTO spacecraft is an essential element in becoming a spacefaring civilization.

When I was reading about the SABRE engine I was surprised that the crucial technology was simply a cooling system. Air traveling at hypersonic speeds gets very hot, and it needs to be cooled down to very low temperatures even while continuing to flow at very high speeds. Also, the moisture has to be extracted from the air, since ice coming into a hypersonic jet could cause serious problems. These are the problems that REL has so far been tackling successfully.

The REL SABRE engine is one solution for an engine that runs as a jet through the atmosphere and then turns itself into a rocket for extra-atmospheric flight. I assume that there are other possible solutions to this technological and engineering challenge, but as far as I know, REL is the only enterprise at present engaged in this kind of research and development. Of course their are always rumors that such things are being developed for the military in “black” programs of which the public knows nothing. It seems to me that if the Skunk Works could build the SR-71 Blackbird in the 1960s, by now they certainly ought to be able to build an air cooler that can aspirate a jet engine to the edge of the atmosphere at hypersonic speeds. Certainly I hope that such research is taking place, since the future of civilization is at stake.

There would be very obvious military advantages to a SSTO fighter, which would also be the first space fighter. Because of the ascendancy of the drone industry in recent years, several military hardware commentators have ventured that the current crop of fifth generation fighters (and 5.5 generation fighters) will be the last of the manned combat jets. I think it is much more likely the the F-22, and F-35, the Sukhoi PAK-FA and the J-20 will be the last generation of atmospheric-only military fighter craft, as the next obvious step is a fighter that takes off from the runway on the ground and flies directly into space, there to defend space-based military assets and to attack and disable the space-based assets of rival military powers.

It is hard to imagine that such developments are not taking place far from the eyes of the public. Hopefully my friends over at Open Source GEOINT will spot something like this soon.

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Grand Strategy Annex

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