From the Telegraph (registration required):
Its [The Pentagon’s] research arm recently solicited bids for a new breed of space-based unmanned hypersonic bombers, capable of taking off from American soil and striking targets on the far side of the globe within two hours, without waiting for permission to use bases, or for overflight rights.
The ultimate aim is to leave America’s enemies in fear of a strike from a clear blue sky at any second or, in the Pentagon’s words, “to hold adversary vital interests at risk at all times”.
Not So Fast 