WALLOPS ISLAND, Va. - A private company contracted by NASA to make supply runs to the International Space Station scrubbed a Wednesday test launch of an unmanned rocket, saying a cord linked to the rocket's second stage apparently detached too soon in blustery winds.

The towering Antares rocket had been scheduled to blast off Wednesday afternoon from Wallops Island on Virginia's Eastern Shore when the countdown clock was halted 12 minutes before a 5 p.m. launch window was to open.

Barron Beneski, a spokesman for Dulles-based Orbital Sciences Corp., said experts were investigating exactly what happened.

Earlier in the day, the launch director for NASA's Wallops Flight Facility granted Orbital permission to proceed with a launch as long as winds didn't exceed 23 mph.

Officials had already shortened the launch window Wednesday amid weather concerns.

The planned launch by the Washington area commercial firm was designed to test whether a practice payload could reach orbit and safely separate from the rocket. Orbital executives have said they are conducting the tests as they prove their capability to carry out several supply runs they contracted for with NASA.

Orbital was one of two commercial companies, along with California-based competitor SpaceX, chosen to supply the space station by NASA, which ended its 3-decade-old shuttle program in 2011.

SpaceX, based in Hawthorne, Calif., was awarded a $1.6 billion contract by NASA in 2006 to make a dozen restocking missions. SpaceX has linked up with the space station three times, though only two of those deliveries occurred under its resupply contract. Its Dragon capsule is the only supply ship capable of two-way delivery.

In 2008, Orbital was awarded a $1.9 billion contract for eight deliveries.

"We've been playing catch up, but we're about caught up," said Frank Culbertson, executive vice president and general manager of Orbital's Advanced Programs Group, had said recently. "By the end of next year we should have an additional four or five cargo missions under our belt, so we're going to be moving fast."