Europe to Australia in less than 5 hours

[altonacrude]

Nitrogen oxide gas is nasty environment-wise, but the amount produced in a hydrogen-air jet engine is likely to be only a few parts per million in the combustion gas, unlike the substantial proportion of CO2 from a conventional jet engine.

At present the most cost-effective way of producing industrial hydrogen is from natural gas, but it's something of a mystery as to why you would want to do that for aircraft fuel. Natural gas is cheaper and a whole lot easier to store. Presumably, use of hydrogen in the envisaged supersonic aircraft depends on new processes for extracting hydrogen from renewable resources.

I can imagine why it's appealing for a European to think of flying to Sydney for lunch at this time of year then back home for dinner, but are there less ostentatious ways of spending a large amount of money? Besides, right now in Sydney it's been raining for more than a week.