The leak rate is small at present, but growing steadily.

The trigger for repair requirements is the current leak rate projected over a consecutive 12-month period rather than the total quantity of refrigerant lost.

However, several tests may be completed in a chamber with an effective pump and low leak rate.

"Again," Mr. Suffredini told reporters, "the leak rate is very small so it makes sense for us to be methodical in everything we're doing."

Better seals can reduce leak rates and pumping power, but may increase friction.

EPA now requires calculation of the leak rate every time that refrigerant is added to an appliance.

This would imply a fast leak rate for the diatomic nitrogen and oxygen.

The best vacuum for a system is achieved when the pump rate equals the leak rate.

But to be cautious, he said, the shuttle crew would start up the suspect unit early Sunday to see if the leak rate gets worse.

Captain Crippen said the leak rate appeared to be stable and would pose no problem for the landing.