Space Shuttle Launch Scrubbed

Today's launch of the space shuttle Endeavour, set for 3:47 p.m., has been cancelled.

Mission managers said two heaters are causing issues with the shuttle's Auxiliary Power Unit.

According to NASA, Commander Mark Kelly and his crew were on their way to the launch pad when NASA halted the countdown.

NASA spokesman George Dillard says the next try will be Sunday at the earliest.

NASA reported earlier that two heaters on an auxiliary power unit were not working. Engineers could not understand the problem, and the launch was halted.

Kelly is married to wounded congresswoman Gabrielle Giffords. She is already in Cape Canaveral. President Barack Obama planned to watch the launch but had not yet arrived.