Fri, 29 Apr 2011 07:51:50 -0500
The shuttle launch team is evaluating an issue with the right Orbital Maneuvering System (OMS) fuel tank pressure. It currently is at 290 pounds per square inch (psi) and the Launch Commit Criteria limit is 288. There also is a difference in pressure between the fuel and oxidizer tanks of 18 psi, and the limit is 15. The oxidizer pressure is 272. All the pressures are stable, and engineers believe the issue may have been caused by a regulator failure to lock up and a leaking helium isolation valve.
Launch controllers will open the crossfeed valve between the left and right OMS systems to help alleviate the pressure, which is expected to clear the issue.