DARPA Falcon HTV-2 Experimental Hypersonic Test Vehicle
The Falcon HTV-2 system is experimenting with Mach 20 speeds, sub-orbital work and unmanned flight - though both developmental vehicles have been lost to date.
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Billed as the "World's Fastest Airplane", the Falcon HTV-2 ("Hypersonic Technology Vehicle") is a long-duration, hypersonic test system currently in development through DARPA (Defense Advanced Research Projects Agency) for the United States Air Force. The program is still in the development and testing phase as of this writing with the overall goal being production of an aircraft able to reach any part of the planet within 60 minutes (DARPA states NY to LA in 12 minutes!). This undoubtedly makes for a very tempting military weapon, the idea being that research will yield a vehicle capable of dropping ordnance against ground targets at will, able to easily evade radar, out-fly interception missiles and reach targets before an enemy can even react.
The Falcon HTV-2 program (known as "Prompt Global Strike") was born in 2003 to help research a delivery vehicle for the United States military with the simple goal of reaching any part of the world in under an hour. Following the design phase, the HTV-2 was produced through computer simulations and wind tunnel testing to evaluated the validity of such a system. Both proved the concept sound though wind tunnel tests were limited to Mach 15 environments and this for only short periods of time. Nonetheless, with funding, DARPA proceeded to construct the real thing. The HTV-2 would be a rocket-launched system, unmanned at its core and controlled from the ground in the same way modern UAVs (Unmanned Aerial Vehicles) are - never putting the pilot in harm's way. The HTV-2 is a research vehicle intended to collect in-flight data for after-mission processing.
The concept of the Falcon HTV-2 is a rather basic one involving delivery of an unmanned aircraft into sub-earth orbit. The vehicle is released from its rocket "booster" system, achieves "self-control" and orientation and proceeds to dive back to earth, in the process reaching speeds of up to 13,000 miles per hour (Mach 20, twenty times the speed of sound). This allows the arrow-head design of the Falcon to literally "slice" through the upper atmosphere at unheard of speeds, essentially making it a hypersonic glider of sorts despite its Mach 20 speed. The aircraft then falls into the ocean in a controlled crash upon completion of its mission. Due to its sub-orbital flight, the body of the Falcon is able to shield itself from the extreme heat - as high as 3,500F degrees - during its high-speed flight at such high-altitudes. Additionally, its aerodynamic principles must be extremely stable and controllable at such speeds for the vehicle to be of any use.
The "piggyback" idea involving a primary "booster" aircraft is not wholly uncommon within United States Air Force lore for the USAF has been using such launch methods throughout a bevy of experimental systems in the 1950s and 1960s. One such method - this involving a modified Boeing B-29 Superfortress - was used to launch the Bell X-1 rocket plane that allowed the Americans to successfully break the sound barrier for the first time. Similarly, the North American X-15 rocket plane was launched from underwing of a Boeing B-52 Stratofortress. The Falcon HTV-2 is launched into sub-earth orbit by way of the Minotaur IV Lite rocket booster.
To Date, the Falcon HTV-2 was successfully launched twice though both vehicles were subsequently lost to failure due to loss of communication. This resulted in uncontrolled crashes of both systems into the ocean. The first flight was attempted in April of 2010, reaching speeds between Mach 17 and Mach 22, while the second - and last publicized flight, occurred on August 10th, 2011 out of Vandenberg Air Force Base in California. The latter flight lasted all but 9 minutes, though valuable data was said to be garnered from the flight before the ill-timed crash including a speed value of 3.6 miles per second.
The Falcon HTV-2's flight is divided into several major phases. The initial phase is the "Launch Phase" which incorporates the Minotaur IV Lite Launch Vehicle as a booster rocket to get the HTV-2 "space-borne". The thrust forces available in the Minotaur IV system allow the Falcon to reach its intended near-orbital speed and altitude. Following launch and after achieving the desired altitude reach, the HTV-2 aircraft separates from the rocket booster, switching to its Reaction Control System (RCS) to orient itself in its near-orbit environment - this called the "Reentry Orient Phase" - and makes use of thrusters built into the design (in the same way the Space Shuttle could orient itself outside of the atmosphere). Upon reaching self-control, the HTV-2 then goes into its "Reentry Phase" which sees it in a controlled dive back towards the earth. The HTV-2 then enters the "Pull-Up Phase" which is essentially the HTV-2 orienting itself upwards to a desired speed. The "Glide Phase" is next and this is where theHTV-2 really shines - achieving unheard of speeds to reach any point on the planet in an hour or less. Up to now, this period has been used to test the validity of internal systems, flight-control, data collection and aerodynamic qualities at extremely high speeds though military applications abound. After flight, the aircraft enters the "Terminal Phase" in which the HTV-2 simply rolls over and dives into a predetermined area in the ocean, ending its mission as planned. A recovery crew then collects the aircraft for reuse.
The Minotaur IV Lite Booster Rocket
The Minotaur IV Lite is a further development of the Minotaur IV rocket family. The Minotaur IV itself was developed from the "Peacekeeper" series of missiles to a Untied States Air Force requirement for an expendable launch system capable of reaching Low Earth Orbit. The "Lite" version of the Minotaur IV utilizes a three-stage process with solid fuel and its altitude reach is suborbital. To date, the Minotaur IV series has completed three successful launches, its first which carried the HTV-2 system. Each launch costs American tax payers $50 million, making for one expensive "expendable" launch system.
In September of 2007, it was announced that the United States Air Force green-lit the "Blackswift" project, a fighter-sized unmanned hypersonic aircraft designated as the HTV-3X. However, the program as cancelled in October of 2008 due to a lack of funding. The original HTV-1 was conceptualized but eventually cancelled prior to the HTV-2 coming online.