In this photo provided by NASA,, the space shuttle Endeavour sits on Launch Pad 39-A at the Kennedy Space Center in Cape Canaveral, Fla., Friday, April 29, 2011. Friday's launch attempt was scrubbed due to a faulty power unit heater. (AP Photo/NASA, Kim Shiflett)

(AP) -- NASA says a switch box removed from space shuttle Endeavour has a blown circuit.

The repair work is taking longer than expected. That means Endeavour's on the next-to-last shuttle flight may face yet another delay. currently is targeting a launch for next Tuesday at the earliest.

Endeavour was supposed to blast off last Friday. But fuel-line heaters did not turn on during the final part of the countdown. The problem was traced to the switch box. A replacement was installed Wednesday, but more testing is needed.

Endeavour's final voyage is under the command of Mark Kelly, husband of wounded Rep. Gabrielle Giffords. She plans to return to Florida once the launch is rescheduled.

More information: NASA: http://www.nasa.gov/shuttle