Clearest view of Columbia's damage

The Columbia Accident Incident Board (CAIB) has released the most detailed image yet of the launch incident that damaged the space shuttle's wing, possibly fatally.

The processed and enhanced frames from a launch pad video camera show a tumbling piece of foam insulation breaking off the large external fuel tank and striking the orbiter's left wing at 853 km/h (530 mph).

Experiments in which foam samples have been fired at shuttle heat-shield tiles have so far failed to provide the direct evidence that would link the launch incident with the catastrophic failure of the shuttle on 1 February.

Experts say further testing will be done next month.

It is thought the piece of foam debris cracked or breached one of the panels that comprise the leading edge of Columbia's left wing, or damaged the so-called T-seal between two adjacent panels.

Damage potential

This allowed superheated air to enter the wing when Columbia re-entered the atmosphere. The wing was destroyed and Columbia disintegrated with the loss of its seven crewmembers.

The new video frames have highlighted to some investigators the need to consider the foam fragment's spin - a factor up until now not considered - which they think may have increased its potential to cause damage.

Initial tests firing foam fragments at shuttle tiles at the Southwest Research Institute in Texas have shown only limited damage, but experiments using larger foam pieces, fired at a wing sample from shuttle Discovery, will begin next month.

Meanwhile, Nasa's Associate Administrator for space flight, William Readdy, who has been conducting an internal agency investigation into the accident, has been focusing on previous serious shuttle incidents.

New examination

This includes the launch of shuttle Atlantis last October.

During lift-off, a piece of foam from the external tank came away from the same region as that which broke off during Columbia's launch - it struck the left booster without damage.

Also during that launch, there was a failure in one of the data cables that sent commands for the launch pad clamps to release Atlantis when its rockets fired. This left vital command in the hands of just a single cable.

Had the backup cable failed, there would have been a catastrophic launch pad explosion with Atlantis tethered to the ground.

Although Nasa looked at the incident at the time, the new attitude to failures ushered in by the Columbia accident is prompting a closer look at data that previously suggested problems with the data cables.

The CAIB has also reviewed foam separation incidents in previous shuttle lift-offs.

These appear to have happened on at least six shuttle flights. However, for 39 of the shuttle's 113 launches, the region where the foam comes away was not observed, which means that there could have been more incidents.

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