Chief astronaut begins weather reconnaissance

NASA Chief Astronaut Steve Lindsey will soon climb into a T-38 jet to begin flying weather reconnaissance around Kennedy Space Center.

Lindsey will provide real-time observations to help forecasters make a "go" or "no-go" decision for a 6:51 p.m. launch.

Later, he'll switch to a modified Gulfstream II known as the Shuttle Training Aircraft, which will focus on conditions around the three-mile shuttle landing strip.

Showers and thunderstorms must be outside of a 20-mile radius from the north and south ends of the runway, in the unlikely event Endeavour needed to return to KSC during an aborted launch.

The RTLS abort, or Return to Launch Site, has never happened before and is considered extremely dangerous. It might be necessary if one of Endeavour's three main engines failed in the first four minutes and 20 seconds of flight.

Four of seven Endeavour astronauts are now on board Endeavour and strapped into seats: commander Mark Polansky, pilot Doug Hurley and mission specialists Tom Marshburn and David Wolf.

The shuttle hatch is scheduled to be closed around 4:45 p.m.

A shower that was being watched to the west of KSC has dissipated and is no longer a concern, NASA says.