Ian Shephard/London

The US Air Force is to award a $50 million engine development contract for its HyTech hypersonic missile programme by the end of 1997, which could lead to a Mach 7-8 weapon being fielded as early as 2009.

Speaking at the Towards Mach 5: Hypersonic Flight conference in London on 3-4 November, Bob Mercier, chief of the Hypersonic Technology Office at the Air Force Research Laboratory in Dayton, Ohio, said that a choice would be made in December between the supersonic combustion ramjet (scramjet) proposals of Pratt & Whitney and Gencorp Aerojet.

Full details of the Boeing Mach 8 missile design have not been released, but Mercier indicates that it will be a lifting-body vehicle, using a solid booster to accelerate to Mach 4, where the scramjet would ignite.

The USAF is interested in developing a rapid-response stand-off missile to attack high-value mobile targets, while also developing a weapon which is difficult to defeat in terminal-phase engagements.

The Boeing design is now at the "initial-freeze" stage, says Mercier, but will require "one more iteration", depending on the engine.

Both engine proposals are scramjets and use "storable" hydrocarbon fuels to make the weapon safe for under-wing carriage, and have shock-inducing augmentors to start as previous additives were "environmentally unfriendly".

P&W proposes a sidewall injector design with a fuel cooled combustor, while Aerojet uses in-flow struts to inject fuel, and radiatively-cooled ceramic matrix composities.

The HyTech programme may break the 30-year impasse in hypersonics technology caused by combustor instability, and bring closer re-usable, manned hypersonic vehicles.

Source: Flight International