DARPA announced this week that it was ready to give the Falcon Hypersonic Technology Vehicle 2 or HTV-2 its next test flight. The HTV-2 is a prototype weapons platform that was created with the goal of making a weapon that could strike anywhere on Earth within an hour. The HTV-2 would travel at 13,000 mph and would need only 12 minutes to get from New York to LA.

The stresses during the test flight are intense. The outside of the HTV-2 would reach a temperature of 3,500F during the flight, which is hotter than a blast furnace used to melt steel. The second flight of the HTV-2 was scheduled for today with a launch window between 7am and 1pm PDT. However, the launch has been postponed until tomorrow. The craft will lift off from Vandenberg AFB in California aboard a USAF Minotaur IV rocket.

“Assumptions about Mach 20 hypersonic flight were made from physics-based computational models and simulations, wind tunnel testing, and data collected from HTV-2’s first test flight—the first real data available in this flight regime at Mach 20,” said Air Force Maj. Chris Schulz, HTV-2 program manager who holds a doctorate in aerospace engineering. “It’s time to conduct another flight test to validate our assumptions and gain further insight into extremely high Mach regimes that we cannot fully replicate on the ground.”

This is the second flight of the HTV-2 vehicle. The first test flight was considered a partial success after the HTV-2 was able to launch, reached its Mach 20 speed, and collected a bit of data before losing contact and being lost in the ocean roughly nine minutes after takeoff. The initial flight was long enough for the collection of some data on the performance characteristics of the aircraft.

“Wind tunnels capture valuable, relevant hypersonic data and can operate for relatively long durations up to around Mach 15. To replicate speeds above Mach 15 generally requires special wind tunnels, called impulse tunnels, which provide milliseconds or less of data per run,” Schulz said. “To have captured the equivalent aerodynamic data from flight one at only a scale representation on the ground would have required years, tens of millions of dollars, and several hundred impulse tunnel tests.” According to Schulz, impulse tunnel testing is required to create a portion of Mach 20 relevant physics on the ground."

For the test flight set for tomorrow, engineers changed the HTV-2 center of gravity, decreased the angle of attack flown, and will use an onboard reaction system to augment the flaps on the vehicle to maintain stable flight. The Minotaur launch rocket will take the HTV-2 to near orbital altitude and then release the HTV-2 to fly on a hypersonic glide trajectory.