The US Air Force has announced that it will carry out the first supersonic flight powered by Gas-To-Liquid (GTL) synthetic fuel tomorrow. A 1980s-vintage B-1 "Lancer" swing-wing bomber will take off from Dyess air force base in Texas, filled up with a 50/50 mix of ordinary petroleum jet juice and synthetic, and go supersonic above the White Sands Missile Range in New Mexico.

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This stage of the idea isn't environment-friendly in any way: the Fischer-Tropsch GTL process used to turn natural gas into liquid involves burning large proportions of the initial feedstock, so that a synthi-fuel powered flight is actually more carbon-intensive than a normal one.

Rather than seeking to save the planet, the USAF is at present seeking to free itself from the vagaries of the global crude oil market. Not only are prices extremely high at present, much of the world supply comes from troublesome regions such as the Persian/Arabian Gulf, Nigeria etc.

And indeed, the US military is also seeking tech which could get jetfuel from alternative feedstocks - such as algae scum or even mushrooms - which could potentially be carbon-neutral one day.