The Falcon HTV-1 program, which preceded the Falcon HTV-2 program, was conducted in April, 2010. The mission ended within nine minutes from launch. Both these missions are funded by the US Defense Advanced Research Projects Agency to help develop hypersonic technologies and to demonstrate its effectiveness. Under the original plan, HTV-1 was to feature a hypersonic lift-to-drag ratio of 2.5, increasing to 3.5-4 for the HTV-2 and 4-5 for the HTV-3. The actual lift-to-drag ratio of HTV-2 was estimated to be 2.6. HTV-2 was to lead to the development of an HTV-3X vehicle, known as Blackswift, which would have formed the basis for deployment around 2025 of a reusable Hypersonic Cruise Vehicle, an unmanned aircraft capable of taking off from a conventional runway with a 5,400 kg payload to strike targets 16,650 km away in under 2 hours. The HCV would have required a lift-to-drag ratio of 6-7 at Mach 10 and 130,000 ft.
Design
Development of protection structures that are tough and lightweight, development of an aerodynamic shape that has a high lift to drag ratio, development of automatic navigation control systems etc. were some of the initial technical challenges that had been overcome in the final design. The various departments involved in designing the vehicle included aerothermodynamics, materials science, hypersonic navigation, guidance and control systems, endo- and exo-atmospheric flight dynamics, telemetry and range safety analysis. The craft could cover, the distance between London and Sydney, in 49 minutes. Built by Lockheed Martin Corp, the HTV-2 is made of carbon composite material; the durability of such material was needed to prevent important internal components from being destroyed because they are a few inches from its surface. The surface temperature of the HTV-2 was expected to reach or more in flight; steel melts at.
Flight testing
Both flights reached Mach 20 and lost telemetry at 9 minutes of a planned 30-minute mission. The HTV-2's first flight was launched on 22 April 2010. The HTV-2 glider was to fly across the Pacific to Kwajalein at Mach 20. The HTV-2 was boosted by a Minotaur IV Lite rocket launched from Vandenberg Air Force Base, California; the glider was carried inside the nose of the Minotaur IV Lite rocket into outer space with a launch altitude of. The flight plan called for the craft to separate from the launch vehicle, level out and glide above the Pacific at Mach 20. Contact was lost with the vehicle at nine minutes into the 30-minute mission, and the glider's skin disintegrated. In mid-November, DARPA stated that the first test flight ended when the computer autopilot "commanded flight termination" after the vehicle began to roll violently. A second flight was initially scheduled to be launched on August 10, 2011, but bad weather forced a delay. The flight was launched the following day, on 11 August 2011. The unmanned Falcon HTV-2 successfully separated from the booster and entered the mission's glide phase, but again lost contact with control about nine minutes into its planned 30-minute Mach 20 glide flight. Initial reports indicated it purposely impacted the Pacific Ocean along its planned flight path as a safety precaution. The glider's surface reached and controlled itself for 3 minutes before crashing.
Future development
DARPA does not plan to conduct a third flight test of the HTV-2. The decision was made because substantial data was collected from the first two flights, and a third was not thought likely to provide any additional valuable data for the cost. The first flight provided data in aerodynamics and flight performance, while the second provided information about structures and high temperatures. Experience gained from the HTV-2 will be used to improve hypersonic flight. Work on the HTV-2 will continue to Summer 2014 to capture technology lessons and improve design tools and methods for high-temperature composite aeroshells.
