As I understand it Boeing are also working with the British who are developing Skylon. This aircraft takes off from a normal runway and converts to rocket power at the edge of space , where it is expected to achieve Mach 25. Whereas, in atmosphere, as a ram jet, it will travel at up to 4500 miles per hour and to do this they have to reduce the friction temperature of the air at the intakes from up to 3000c down to minus about 150c in one twentieth of a second, and they have proved that they could do that when they blasted ex fighter jet engines straight into the air intake of the Skylon engine and it successfully cooled it down to the working temperature. In atmosphere whilst under jet power and it will extract oxygen from air and freeze it to mix with preloaded liquid hydrogen,t when it switches to the rocket part of its journey. Initially the payload into space maybe a weak point at about 10 tons, but of course you could always build a bigger version of the aircraft with more lifting power. It seems to offer a viable alternative to rockets, especially as it can land and take off a. many times as they need it to in the same day. Currently the non-stop journey to Eastern Australia from the UK is 30 hours. The Skylon is scheduled to do it in about 4 and a half hours, and that would be just using its jet engines. Whatever, it sounds a lot cheaper than the current rocket alternative . Search words 'reaction engines'