NASA engineers are testing a leaky helium valve on the space shuttle Discovery to see if the shuttle can still launch to the International Space Station next month or if it must stand down for repairs.
Discovery is slated to launch a crew of seven astronauts on a cargo delivery mission to the space station on April 5, but shuttle technicians must determine the spacecraft is ready to fly in the next few days to maintain that launch target.
The helium leak was detected Friday as engineers vented Discovery's two aft-mounted thruster systems while preparing to load them with propellant. That was when fuel helium tank pressure on Discovery's right side reaction control system unexpectedly dropped, suggesting that one of two critical isolation valves is either leaking or stuck open when it should be closed.
NASA spokesman Allard Beutel told Space.com that engineers were able to complete the fueling operation after manually closing the valves.
"We physically, manually closed the isolation valves, so we know they work," Beutel said. NASA wants to be sure the valves will work as designed once the shuttle Discovery reaches space, he added.
Discovery's aft thrusters are located to either side of the shuttle's tail near pods that contain larger engines. They include reaction control thrusters for fine adjustments in space.
Engineers plan to test two helium system regulators, which are downstream of the faulty valve, to help make a decision on whether a repair will be required.
"Knowing whether the regulators are operating correctly is a key factor for managers who must decide whether to launch with the errant condition of the isolation valves," NASA officials said in a statement.
That test is slated for later this week, they added.
When NASA hauled Discovery to the launch pad on March 3, the space agency had more than a week of cushion time to handle any unexpected glitches and still maintain an April 5 launch target. There are still a few days remaining in that cushion, Beutel said.
The valve tests have delayed plans to deliver Discovery's cargo to the shuttle's seaside launch pad at the Kennedy Space Center in Florida. That move was slated for this morning, but has been rescheduled for early Friday, Beutel said.
Top NASA shuttle managers are also slated to meet next week to select a firm launch target for Discovery, but that decision may hinge on the result of this week's tests.
Discovery's 13-day mission to deliver fresh supplies, refrigerator-sized racks of science equipment and other gear is one of NASA's four final shuttle missions before the space agency retires its three-orbiter fleet later this year.
NASA has launched one shuttle flight this year – last month's two-week flight aboard Endeavour – to deliver a new room and stunning observation deck to the International Space Station.
Any delay to this mission could have a ripple effect down the line for the remaining three missions, which are slated to launch May 14, July 29 and Sept. 16.
Discovery is also currently scheduled to make that final spaceflight, which will deliver supplies and a permanent cargo module to essentially serve as a spare closet for space station astronauts.