US hypersonic aircraft projects face change as Congress urges joint technology office

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By Graham Warwick in Washington, DC

Prompt global strike project abandons first test vehicle as US Congress considers research consolidation

A key US hypersonics programme is undergoing changes even as Congress urges the creation of a joint technology office to co-ordinate fragmented US high-speed research.

The changes affect the US Defense Advanced Research Projects Agency’s (DARPA) Falcon programme to demonstrate technology for responsive spacelift and global strike. With cutbacks in NASA funding, Falcon has taken on a leading role in US hypersonics and could be affected by any Congressional directive to consolidate research.

DARPA and prime contractor Lockheed Martin have decided not to build and fly the first version of the Falcon hypersonic test vehicle (HTV) after encountering difficulties manufacturing the carbon-carbon aeroshell. Instead, they have shifted efforts to a more producible design for the second in a series of test vehicles, HTV-2, says DARPA Falcon programme manager Dr Steven Walker.

Falcon is focused on demonstrating aerodynamic, materials and guidance, navigation and control technology for unmanned, long-duration hypersonic vehicles. Plans call for a series of rocket-boosted, gliding test vehicles with increasing hypersonic lift-to-drag ratio and flight duration.

Two expendable HTV-1s were planned as the first step, but subcontractor C-CAT experienced delamination problems with the curved leading edges of the carbon-carbon aeroshell, says Walker. Work has shifted to the HTV-2, which will have a multi-piece aeroshell with sharper, thinner leading edges and will be easier to fabricate and assemble. “All parts of the -2 aeroshell fit within C-CAT’s experience base,” he says. “It will not take as long to build.”

The change will delay a first flight from 2007 for the HTV-1 to late 2008 for the first of two ground-launched, expendable HTV-2s. These will be followed by a reusable HTV-3 closer in design to the objective hypersonic cruise vehicle (HCV). The Mach 10 HTV-3 will be unpowered, but Walker says DARPA has received funding to develop and ground test a propulsion system for the HCV.

Walker says Lockheed has selected a high-Mach turbine engine and supersonic-combustion ramjet (scramjet) for a combined-cycle powerplant enabling the HCV to take off from a runway and accelerate to a hypersonic cruise. Tests of the “inward-turning” inlet and scramjet are planned for later this year.

DARPA is also co-funding the US Air Force Research Laboratory’s (AFRL) Boeing X-51A scramjet engine demonstration, which will flight test a Pratt & Whitney hydrocarbon-fuelled scramjet at speeds exceeding M6.5. Five to eight flights of the air-launched, rocket-boosted, expendable X-51 are planned between December 2008 and January 2009.

AFRL and DARPA plan to integrate the HyTECH scramjet with an M4 expendable turbine engine, HiSTED, for a combined-cycle ground demonstration that could lead to flight tests of a large-scale hypersonic cruise X-vehicle. Walker says the HySTED/HyTECH combination is an alternative to the HCV propulsion system being pursued by Lockheed.