Falcon Hypersonic Technology Vehicle 2

The Falcon Hypersonic Technology Vehicle 2 (HTV-2) program was a multiyear research and development venture by Darpa to increase the knowledge base and advance critical technologies towards long-duration hypersonic flight. Falcon HTV-2 is an uncrewed, rocket-launched, maneuverable aircraft that travels through the atmosphere at incredibly high speeds—Mach 20 (approximately 13,000 miles per hour). A research vehicle, HTV-2 has numerous sensors collecting data in an uncertain operating envelope.

The program, known as "Prompt Global Strike," began in 2003 to research a delivery vehicle for the United States capable of reaching any part of the world in under an hour. Following a design phase, the vehicle was produced using computer simulations and wind tunnel testing, which proved the concept sound, although wind tunnel testing was limited to Mach 15 environments for short periods of time. After the design was validated, DARPA proceeded to construct the prototype vehicle. The concept behind the vehicle utilizes a rocket booster system (Minotaur IV Lite Launch) for launch before achieving "self-control," orientation, and diving back to Earth, reaching speeds up to Mach 20. Its sub-orbital flight means the body of the Falcon is able to shield itself from extreme heat.

Image of the Falcon HTV-2 design.

Data from the HTV-2 program informs the policy, acquisition, and operations decisions of future Department of Defense Conventional Prompt Global Strike programs. Hypersonic data was collected through extensive modeling and simulation, wind-tunnel testing, and experimental test flights. Long-duration hypersonic flight requires overcoming three major technical challenges: aerodynamics; aerothermal effects; and critical guidance, navigation, and control.

HTV-2 flew its maiden flight on April 22, 2010, collecting nine minutes of data, including 139 seconds of Mach 22 to Mach 17 aerodynamic data, before the vehicle lost communications and crashed into the ocean. At the time, HTV-2's first flight achieved the following:

• The largest number of sea, land, air, and space data collection assets in support of hypersonic flight test
• Maintaining GPS signals while traveling 3.6 miles per second
• Two-way communication with the vehicle
• Effective use of the Reaction Control System (RCS)

The Falcon HTV-2 vehicle launched from Vandenberg Air Force Base, California, using existing rocket booster systems. After booster separation, the HTV-2 glided at hypersonic velocities in the upper atmosphere above the Pacific Ocean.

HTV-2 had its second test flight on August 11, 2011. DARPA asserted the craft managed to travel at Mach 20 for roughly three minutes before experiencing a technical problem and crashing into the Pacific Ocean. Several days after the crash, then DARPA director Regina Dugan stated,

HTV-2 demonstrated stable, aerodynamically controlled Mach 20 hypersonic flight for approximately three minutes.

HTV-2 encountered an anomaly of undetermined origin, causing the vehicle's autonomous flight safety system to engage, directing the aircraft to initiate a controlled splashdown. DARPA released footage of the test in August 2011. The video was taken by a crewmember on a tracking ship. It shows the rocket and vehicle together as a fast-moving contrail and then the HTV-2 alone. The test flight launched from Vandenberg Air Force Base.

Footage from HTV-2's second test flight.

On April 20, 2012, DARPA released a statement saying that a March 20, 2012, test flight of the HTV-2 failed due to issues at extremely high speeds. Launched from Vandenberg Air Force Base, the HTV-2 was expected to travel westward for roughly thirty minutes before crashing into the Pacific Ocean near Kwajalein Atoll, some 4,000 miles from departure. However, nine minutes into the flight, after reaching Mach 20 speeds, parts of the vehicle's structure began to peel off. This created strong shock waves around the vehicle, causing it to roll abruptly and fail to recover stability. The anomaly prompted the flight safety system, resulting in a controlled descent into the Pacific Ocean.