The brother of one of the Discovery astronauts has spoken out about the risk of another debris strike on the space shuttle when it launches Saturday.

Scott Kelly is the twin brother of shuttle pilot Mark Kelly. He is an astronaut too — and said he fully expected that insulation foam would again break off the shuttle fuel tank when Discovery blasts off.

Kelly said he'd discussed the risks with his brother, and both felt that the mission should proceed.

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While there are dissenting voices in NASA about the foam problem, Kelly said spaceflight is a risky business and that the risk had been carefully weighed.

Foam debris that damaged a wing was blamed for the Columbia disaster that claimed seven lives in 2003. At the last launch, just about a year ago, foam again broke away from the fuel tank.

Kelly says NASA was ready to capture every bit of foam with multiple cameras, so engineers could take corrective steps for future missions.