NASA engineers are examining seals known as O-rings that go between space shuttle booster rockets.
Recent batches have shown a higher-than-usual amount of unmixed rubber. The seals are of special concern to the U-S space agency since their failure was blamed for the 1986 Challenger disaster. The shuttle blew apart 73 seconds after liftoff when seals that had stiffened from cold weather allowed hot gases to escape the booster and ignite fuel.
Rubber specks that are too large or too close together can make the seals stiffer. Space shuttle Endeavour is set to launch on August 7th for a mission to the International Space Station.
A NASA spokesman says engineers are checking to make sure the O-rings in Endeavour's boosters aren't part of the batches under examination, but they don't expect them to be.