A 4 cm (1.5 inch) piece of debris can be seen just after falling away from one of the orbiter鈥檚 heat-resistant tiles
The falling chunk of debris, on the left between the orange external tank and the black orbiter, did not strike the shuttle itself
The nose cone of the orange external tank struck the large bird just 2.5 seconds after launch
NASA is investigating two 鈥渄ebris鈥� incidents which could have left the space shuttle Discovery damaged after its launch on Tuesday.
Shortly after reaching orbit, Discovery Commander Eileen Collins told Mission Control in Houston, Texas, that it was 鈥渂y far the smoothest ascent鈥� of her four shuttle flights. But video footage revealed that the launch had not been as smooth as NASA might have wished.
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The incident that poses the highest risk is the discovery of damage to a 22-centimetre-wide (8.5 inch) heat-resistant tile on the edge of the door enclosing the shuttle鈥檚 nose landing-gear. Radar analysis, and then video footage from a camera mounted on the external fuel tank, revealed that a patch of the surface about 4 cm (1.5 inches) across is missing. The seal around the hatch enclosing the landing gear is known to be an area where any damage would be especially worrying.
It was damage to the heat shield on the shuttle Columbia which led to its ultimate destruction during re-entry to Earth鈥檚 atmosphere in February 2003. Superheated gas entered a breach in the craft鈥檚 left wing, which had been struck by a piece of insulating foam that fell from the external tank during take-off.
However, minor damage due to falling debris has been a common occurrence on shuttle flights. The flight operations manager for the shuttle, John Shannon, said it was not yet possible to say if this damage was a safety issue.
鈥淧ersonally, I feel very good about where we are at in this mission right now,鈥� Shannon said. Wayne Hale, deputy shuttle program manager, said he expected to know whether the shuttle had sustained critical damage during launch by day six of the mission.
Damage depth
After the Columbia disaster, NASA followed recommendations to redesign the tank to reduce the risk of falling debris. But it could not ensure that no debris would be shed.
Another innovation was to significantly increase the observation of the shuttle during launch from the ground and air. More that 100 official cameras recorded the launch. Those images are now be being analysed, with a key question being how deeply damaged the tile is.
On Wednesday another new feature will begin use, when astronauts operate a new extension to the shuttle鈥檚 robot arm to inspect for damage. But the first day鈥檚 work will not cover the area of the damaged tile.
If it turns out that the tile damage is serious, NASA鈥檚 preferred option is to keep the crew on the International Space Station until a second shuttle is ready to fly a rescue mission. There are repair kits on board, but NASA鈥檚 intention was only to test the kits, rather than use them to repair real damage.
Unprecedented observation
The second debris incident occurred at the same time as the tile-portion came away, at 2 minutes and 5 seconds after launch and just after the solid rocket boosters on the side of the external tank separated.
But there was good news in this case. 鈥淚t did not hit the orbiter, it cleared the stack with no problems,鈥� said Shannon. He points out that the unprecedented observation of the launch means 鈥渨e are seeing areas of the vehicle we have never seen before鈥� and that such debris falls 鈥渃ould occur on every flight鈥�.
It is not clear if the falling object was a piece of foam or something else, or even what size it was. 鈥淚t鈥檚 hard to tell whether it is a bigger piece far away, or a smaller piece close in,鈥� said Shannon.
There was also an impact on the shuttle within 2.5 seconds of lift-off, when a large bird was struck and killed by the nose cone of the external tank. The bird might have been an osprey or a turkey buzzard, but did not damage the tank, NASA officials said.
Discovery鈥檚 mission will end on 7 August when it is due to land in Florida at 0546 EDT (0946 GMT).
