Rocket-launched hypersonic bomber falls into the sea

DARPA, the Pentagon's research branch, has done it again. It has lost another uncrewed hypersonic bomber in a test flight over the Pacific Ocean.

At issue is the fate of DARPA's "Falcon" Hypersonic Technology Vehicle 2 (HTV2), which, like the now-retired space shuttle and the nascent uncrewed X-37 spaceplane, is a rocket-launched glider.

Its aim is to deliver a bomb from anywhere in the continental US to any other point on the planet in an hour or less. Launched on a Minotaur rocket, it is released at great (though suborbital) altitude to glide at Mach 20 (21,000 kilometres per hour) to a target.

The trouble is that even in the ultra-thin atmosphere at such altitudes the tremendous speed heats the aircraft's skin to around 2000 °C. That creates unknown problems with aerodynamic, electrical and guidance systems - so a programme of incrementally more ambitious flight tests has to be undertaken to understand them.