CAPE CANAVERAL, Fla. — A last-minute technical issue forced NASA officials to scrub the launch of space shuttle Endeavour at about noon today, a move certain to disappoint President Barack Obama, U.S. Rep. Gabrielle Giffords and hundreds of thousands of spectators who flooded to Florida’s Space Coast.

The issue is one of three heating units aboard Endeavour that is designed to keep fuel lines from freezing in space. While these fuel lines are not particularly critical for launch, they are vital in ensuring that the airplane-like machinery of Endeavour works on re-entry — such as landing gear and its rudder speed brake.

“You don’t want frozen fuel lines, obviously,” said NASA spokesman Allard Beutel.

A short circuit has emerged as a primary suspect, but NASA engineers are not 100 percent certain. Hints of a problem started appearing earlier Friday morning. It may take until Saturday morning, however, until technicians are able to access the broken piece.

Endeavour was set to blast off for a 14-day mission to bring the long-delayed Alpha Magnetic Spectrometer to the International Space Station, along with critical supplies, spare parts and equipment. Then, like Discovery, it will slip off into retirement.