Forgive our overzealousness, because just two days from when we first covered the hypersonic jet X-51A WaveRider – a craft capable, in theory, of reaching speeds of five times the speed of sound – the US Air Force has revealed that its latest test has ended in unceremonious failure.

Tuesday’s test - in which the X-51A was carried to over 50,000ft above sea level by a B52 bomber, before being dropped to fire itself to hypersonic speeds – is the very latest of three failed attempts by the military to test the ‘scramjet’ technology that fuels the expectant hypersonic speeds of the jet. It is feared this test could well be its last, while also proving likely in putting promises of hypersonic flight to bed for quite some time yet. Here’s how we described the US military expected the test to pan out;

During the test, the X-51A will be flown from Edwards Air Force Base in the Mojave Desert in California to around 50,000ft above the Pacific Ocean by a B52 bomber, before being dropped and free-falling for around 4 seconds. It is at that point that the hypersonic jet will fire its rocket booster, accelerating the craft to Mach 4.5 (3,425mph) before being jettisoned. Only then will the revolutionary ‘scramjets’ be ignited, pushing the WaveRider to its top flight speed of more than 4,000mph and propelling it to around 70,000ft.

The test will last a total of just 300 seconds, before the jets are switched off and the X-51A plummets to the bed of the Pacific Ocean, never to be recovered.

Only, it didn’t quite go to plan. In what could represent a loss of almost $300 million in Pentagon funding, the US Air Force said in a statement Wednesday that a faulty control fin caused a loss of control and prevented the jet from firing up its highly-ambitious ‘scramjet’ engine. Just 15 seconds after separating from its rocket booster – which propels the X-51A to speeds of around 3,000Mph, before the scramjet does the rest to push the missile to Mach 5 – the WaveRider broke apart.

It was in fact the X-51A’s first test flight that has proved to be the most ‘successful’ test in 2010, in which the vehicle reached Mach 4.88 and boasted 143 seconds of its total flight time (a modest 210 seconds) under scramjet power. It remains to this day the longest ever hypersonic flight. The X-51A’s second test was decidedly less impressive, with a problem in the engine resulting in the ethylene fuel that is need to start the scramjet not correctly switching over to the JP-7 fuel needed for sustained flight, causing the engine to shut down. A short trip to the bottom of the Pacific Ocean shortly followed...

As for what lies ahead, the hard truth is that there is now only one X-51A vehicle left in existence. The baton is now passed to the US Air Force who will have to decide in the months to come whether it will fly, or whether the project will be scrapped. Here's hoping it's the former.

Richard Birkett