Was the shuttle struck by lightning?

High-altitude lightning may have caused the loss of the space shuttle Columbia, a British academic claimed yesterday.

Dr David Harland suggested that a gigantic electrical discharge called a 'sprite' could have fatally damaged the craft.

The theory is backed up by photographs taken by an amateur astronomer as the shuttle re-entered the atmosphere over San Francisco on Saturday, just seven minutes before its demise.

The pictures - described by the unnamed photographer as five 'strange and provocative images' - have not yet been publicly released.

But they show a bright, scraggly flash of orange light tinged with pale purple, shaped like a deformed letter L, 'zapping' the shuttle from behind.

It could not have been conventional lightning, as Columbia was far too high.

But sprites - a weird and beautiful-but little-understood atmospheric phenomenon - flash into space high above ordinary thunder clouds.

Originally, Nasa scientists were working on the theory that pieces of foam insulation seen striking the spacecraft's left wing at launch may have dislodged some of the heatresistant tiles, leading to a catastrophic burn- up on re-entry.

However Ron Dittmore, Nasa's shuttle programme manager, said yesterday that the foam theory 'doesn't make sense'.

The foam was too light, and travelling too slowly, to have caused sufficient damage.

'There has got to be another reason.' He said Nasa was now looking for 'the missing link' to explain the accident, which led to the loss of seven astronauts and the suspension of America' s manned space programme.

According to Dr Harland, the missing link could be a sprite.

The academic, an expert on the space shuttle and a historian of Nasa and Soviet space missions, said: 'This is a very intriguing possibility. If it was hit by a sprite, it would have blasted off tiles and fused metal.'

Nasa confirmed yesterday that sprites are one of the possibilities being considered by crash investigators.