Saturday, May 1, 2010

Out-of-control balloon grounds further NASA flights

Balloons may seem like a serene way to fly. But getting them off the ground can be another matter, as a violent launch mishap last week demonstrates.

On Thursday, an American and Taiwanese team was poised to use a giant, NASA-sponsored balloon to carry the Nuclear Compton Telescope (NCT) some 40 kilometres above Earth's surface. The telescope was designed to map the celestial glow of gamma-ray light produced by sources like aluminium-26, a short-lived isotope forged in stellar explosions.

Instead, the wind carried the 121-metre-wide, helium-filled balloon rapidly across the launch site at Alice Springs, Australia. A gondola containing the $2 million telescope was dragged along the ground, overturning a nearby car and narrowly missing onlookers before finally tumbling to a stop. Watch a video of the accident.

The extent of the damage is still being assessed, but initial reports suggest some components of the telescope, including the probe's electronics bay, were destroyed.

"It's horrible," says astrophysicist Mark Devlin of the University of Pennsylvania in Philadelphia. Devlin lost a telescope called BLAST in 2007 when winds dragged the probe, whose parachutes failed to disconnect on landing, across 200 kilometres of Antarctic ice. "I totally know how they feel."

Rare accident

Wind is a common obstacle to launch, since the tenuous balloons are sensitive to strong gusts. Wind must also blow in the right direction so the balloon can be released properly from its launch crane.

"Conditions need to be pretty good, but mostly what they need to be is stable," Devlin says. "It takes anywhere between 40 minutes to an hour and a half to fill the balloon, and you're basically lining up the balloon in the direction that the wind is going. If all of a sudden the wind shifts, you're in a tough spot."

Despite balloons' sensitivity to weather conditions, launch mishaps like the Nuclear Compton Telescope's have been rare. NASA's Columbia Scientific Balloon Facility, which manages launches around the world, has released more than 2200 research balloons since the 1960s. Roughly 4 per cent of those launches have failed, says David Gregory, assistant chief of NASA's balloon programme.

NASA had planned to send up one more telescope in this year's Australia campaign, but it is pausing to ferret out the cause of last week's incident. "Right now, all flights are on hold pending the investigation of what happened here," says NASA's Mark Sistilli.