Liquid hydrogen/oxygen obviously is, but it takes a significant amount of energy to create the stuff in the first place.

Also consider that many X prize contestants don't run on this sort of mix; many use something carbon-based for the fuel.

They're probably right on that score, but rocket fuel isn't exactly eco-friendly once you get away from the liquid oxygen/hydrogen blends.

The Kazakhs have been whinging about it for years.

It's been my understanding that the problem with emissions from aircraft is not so much the quantity of greenhouse gases (which is comparatively low*), but where they are emitted. CO2 from a car will be partly sequestered by the trees and other ground-level carbon sinks. Planes leave their CO2 high in the atmosphere, where is contributes most to the greenhouse effect, and can't be scrubbed by the plant life.

On this basis, isn't a rocket plane, which goes even higher than a jet airliner, that much less green?

* Low-cost airlines are keen to point out that planes account for only 2% of the global carbon footprint

Q: How many passengers on a wide-body transatlantic jet?

A: Hundreds usually

Q: How many on a Virgin space ship?

A: Ohhh I get it...

Footprint per person buggers it up a bit. Hopefully they'll design a rocket not capable of re-entry. Hang on, there's a Paris angle there...

Perhaps you'd like to read it all again...

two small jet engines on the carrier @ 60 mins and one rubber/Nox rocket @ 30 seconds. IS GREENER than a Fucking Jumbo flying for 12 Hours with four fucking huge engines! talk about bloody obvious. Stop arguing its true. just understand it! and accept it! Funnily enough even when you do the maths for 140 passanger verses 6 passangers its still 'greener' !! ie volume of fuel used per passanger minute. hence the report.

Water is a greenhouse gas and is therefore eco-unfriendly.

...would be to not waste resources taking pointless joyrides into space at all. Talk about an ego-trip...

Surely if this leads to technology enabling the hop out of heavy thick air for London Sydney trips, then it's a good thing. Because the future technology will quickly cover the testing phase in emissions if it works.

Same as as Prius may be a crap car, but one generation creates the next, so research into batteries etc has funding. Eventualy you get a massive payback from the drivers or flyers of tomorrow using the tech covering any false starts or prototypes.

Plus anyone who stands in the way of space exploration just makes my heart sink right to the floor. The idea of greens holding it back is enough to get me mad (in the Groucho Marx imagined argument way).

...without reading the author's name, and hit: "So there's nothing counter-intuitive about a ballistic flight emitting less exhaust overall than a normal in-atmosphere one..." and immediately think: Lewis!! - and sure enough, a glance to the byline shows it is he. You're almost as epic a Lewis as Hamilton, my friend...

>>Same as as Prius may be a crap car, but...<<

Sounds like someone's suffering from Prius Envy.

Don't worry, Peter, if you work hard and save for long enough, maybe you''ll be able to get one of your own, so you can stop slagging them off. Then you'll know the justifiable feeling of superiority as your "Smugmobile" glides effortlessly past those rusting products of obsolete technology queued at the petrol pump.