research suggested a maximum speed of mach 8 for scramjet based aircraft, as the vehicle would generate heat due to atmospheric friction, which would expend considerable energy. the project showed that much of this energy could be recovered by passing hydrogen over the skin and carrying the heat into the combustion chamber: mach 20 then seemed possible. the result was a program funded by nasa, and the united states department of defense (funding was approximately equally divided among nasa, darpa, the us air force, the strategic defense initiative office (sdio) and the us navy).