The conclusion came after a Friday meeting of NASA managers and engineers who have spent the past six weeks running millions of computer simulations and testing various ways ice might strike the orbiter. The launch window opens July 13.
"There are still some areas we're going to continue to watch very closely and will probably continue to look for ways to mitigate those areas in the future, but we believe that it's an acceptable risk at this particular time," Bill Parsons, manager of the space shuttle program, said at a news conference.
Discovery was transported to the pad in April but removed May 26 after NASA determined that potentially deadly pieces of ice could form over an expansion joint on the external fuel tank after the super-chilled fuel was loaded. Managers decided to install a heater at the joint, located along the feed line for liquid oxygen.
Falling chunks of ice could be even more menacing than pieces of the fuel tank's insulating foam, which was responsible for Columbia's destruction during re-entry and the deaths of seven astronauts in 2003.
Because engineers had focused on keeping big chunks of foam from coming off the tank during liftoff, they didn't realize the ice threat until April. NASA officials have tested the effects of ice strikes in wind tunnels and recreated ice striking the orbiter using dense pieces of ice and slushy ice.
Two more meetings next week will determine whether Discovery lifts off on schedule. A task force overseeing return-to-flight efforts has one more public meeting on Monday, and a NASA's readiness review meeting is next Wednesday.
