New Scientist has a good detailed article on the practicality of air breathing plane acting as space ships. They talk about the recently announced Skylon rocket plane as well as scram-jet technology. The conclude that there may be multiple ways to get to orbit but picking the best design requires a better understanding of how cost effective and reliable the vehicles will be. "I think all approaches are on the table," Lewis told New Scientist. Reaction Engines is "looking at one possible combination of engine system, and there's really a much broader range of options we need to explore before we know what to fly up to orbit,". Because scramjets might operate over the widest range of speeds, possibly up to Mach 20, they might be the most effective choice: "The farther you can go in the atmosphere, the greater the advantage will be."
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