Flight testing of the first hypersonic X-43A air-breathing free-flight vehicle has slipped by around three months to the end of next May. The delay follows the later-than-expected arrival of the experimental craft at NASA's Dryden Flight Research Center, Edwards AFB, California.

The 3.6m (12ft)-long X-43A is a key part of NASA's Hyper-X programme, which aims to build a technology bridge to reusable and recoverable vehicles with larger engines. The programme is initially focused on proving the use of air-breathing, hydrogen-powered engine technologies to increase the payload of future hypersonic aircraft (faster than Mach 5), as well as reusable space launchers.

The first test vehicle was originally due to be delivered to Dryden around July, but last-minute concerns over high-risk elements of the programme forced new tests and caused delays (Flight International, 12-18 May).

Paul Reukauf, X-43A deputy project manager, says: "One of the areas was separation between the vehicle and the adapter, and we decided we needed a full-scale separation test at Orbital."

Although the diminutive X-43A is built by MicroCraft of Tullahoma, Tennessee, the booster and adapter that connects the two are the responsibility of Orbital Sciences, which is supplying aversion of its Pegasus launcher to the Hyper-X programme.

"We were looking for something in excess of 7.5Hz and we actually measured between 7.9Hz and 8.1Hz," he adds.

The first two planned flights next year will see the initial X-43As accelerate to Mach 7 after detaching from the air-dropped Pegasus booster. After separating from it at around 100,000ft, the inlet doors will be opened so air can enter the X-43A's scramjet (supersonic ramjet). Slightly diluted hydrogen will be fed into the scramjet, which will combust spontaneously on contact with the air.

Following around 7secs of operation, the cowl doors will be closed and the engine shut off. The X-43A will then go into a high-speed glide, during which it will collect up to 6min of hypersonic aerodynamic data. The second Mach 7 flight is scheduled for around December, with the tests culminating in a Mach 10 attempt in September 2001.

Source: Flight International