An experimental unmanned aircraft that fly at 20 times the speed of sound is to undergo a crucial test flight on Thursday.
The Falcon HTV-2 will be launched on a rocket into space then will glide back down to Earth at speeds of 13,000mph.
The previous test flight lasted only nine minutes before being deliberately crashed as a safety measure due to technical difficulties.
This mission, should it succeed, could set new records in sub-orbital space travel and pave the way for a generation of super weapons.
The rocket carrying the Falcon will take off Thursday, weather permitting, from Vandenberg Air Force Base in California aboard an Air Force Minotaur IV rocket, which is a decommissioned ballistic missile.
The test was originally scheduled for Wednesday.
The Falcon will then separate off and come back down at colossal speeds - it would take less than 12 minutes to fly from New York to Los Angeles, a journey which takes a normal jet more than five hours.