KENNEDY SPACE CENTER -- Space shuttle Discovery is scheduled to take off on May 25, but that date could change.

Officially, Discovery's flight to deliver the Kibo science laboratory to the International Space Station remains on schedule.

However, the external tank for that mission arrived at the Kennedy Space Center on Wednesday, several days late because of bad weather.

NASA administrator Mike Griffin said the delay could be a few days.

It's a concern because the Mars Phoenix landing is also scheduled for May 25.

(Kibo means "hope" in Japanese.)

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