Want to get from New York to Perth in under 4 hours, or maybe just head to outer space on a lark? Reaction Engines' "Skylon" mach 5 spaceplane might be your chariot -- or not. Its scheme of ingesting oxygen from the atmosphere instead of stowing it like a 50-year old modern multi-stage rocket sounds good, but the project's fate may hang on critical new tests. Failure is still a possibility, but if the high-speed,
