Weather officials at NASA's Kennedy Space Center in Florida are tracking a new tropical depression in the Atlantic Ocean that could affect the launch of space shuttle Discovery, currently set for Wednesday.

Tropical depressions are cyclones with a maximum sustained surface wind speed of up to 62 kilometres per hour. Currently named Tropical Depression 5, if it should strengthen into a tropical storm - with wind speeds of about 117 km/hour - it might threaten the space centre early next week. So if Discovery's launch date is delayed for any reason, the storm could force NASA to move the shuttle under cover.

But such a decision depends on many uncertain factors. The first is the tropical depression's future path. Currently, it is forecast to arrive at the island of Hispanola, 1400 kilometres southeast of KSC, by Saturday.

NASA needs about two days to roll Discovery back into the Vehicle Assembly Building (VAB), so that means a roll-back decision could come on Saturday.

But Discovery is currently scheduled to lift off at 1551 EDT (1951 GMT) on Wednesday. So if launch is pushed back, NASA could try again on Thursday. Then, if that failed, it could make another attempt on Saturday. "Right now, it would only be an issue for us if we happen to scrub all three days," says launch weather officer Kathy Winters.

Unacceptable weather

NASA had a close call with Hurricane Dennis last weekend and considered rolling Discovery back into the VAB at that time - but the storm missed KSC and instead made landfall on the western end of Florida's panhandle.

Now, the forecast for launch time on Wednesday shows a 30% chance of unacceptable weather in the form of storms that may come too close to the launch pad. If NASA opts to try for a Thursday or Friday lift off, the odds worsen slightly with a 40% chance of unacceptable weather.

"If we have a scrub for a weather reason, that's something we could reasonably expect for a summer afternoon," NASA test director Pete Nickolenko told reporters on Monday.

Other than the chance of nasty weather, shuttle managers say everything is progressing smoothly with Discovery. Its 12-day mission will deliver supplies to the International Space Station and test out new safety measures put in place after the Columbia disaster in 2003.

On Monday, the seven-member crew will take another look at some of the equipment they will be using on this flight. Commander Eileen Collins and pilot Jim Kelly will also spend part of Monday and Tuesday doing practice runs in the Shuttle Training Aircraft, which simulates landing.