NASA officials have decided to delay the next-to-last space shuttle flight until at least May 16. Such delay is to allow more time to resolve issues with the craft’s heater circuits and electrical wiring.

The Endeavour mission, which will deliver a $2 billion particle physics detector and spare parts to the International Space Station, has been delayed three times after one of the shuttle’s two heater circuits was found to be non-operational four hours before the scheduled liftoff April 29.

Although technicians have not determined the root of the problem, they replaced a faulty switchbox and plan to install and test new wiring, a NASA press release said.

Amid the delays, the shuttle’s trip has also been extended from 14 to 16 days. NASA has until May 26 to launch the mission, or it will be subject to a further delay into June.

“There is still some uncertainty because we have to get past all the work. We’ll regroup on Monday and see how far they’ve gotten over the weekend, but the looks pretty good right now,” NASA spokesman Kyle Herring told Reuters on May 6.

Shutttle Commander Mark Kelly, a Navy captain and husband of Arizona Congresswoman Gabrielle Giffords (R), who was shot during a political event in Tucson, Arizona last January, will lead Endeavour’s six-man crew.

Giffords attended the April 29 launch attempt and her staff told the AP she will return to see the Endeavour finally lift off.

A final mission for NASA’s 30-year-old shuttle program is expected to launch June 2, but could be pushed back because of Endeavour’s repeated hold-ups.