NASA aborted the launch of a trio of microsatellites on Wednesday just moments before they were to be fired into space aboard a rocket.

The 55-pound ST5 satellites, which were to test new technologies for future science missions, were carried aloft about 6 a.m. from Vandenberg Air Force Base aboard a Lockheed L-1011 jet.

When the plane reached 39,000 feet, a compact Pegasus rocket was to detach from the aircraft's belly and ferry the satellites on a 10-minute climb into space.

But a technical glitch caused NASA to scrub the rocket release, according to a broadcast on the space agency's television station.

The agency said the problem was caused by a locking pin in the rocket's flight control, which failed to retract before launch.

The jet headed back to Vandenberg. NASA officials said the launch would be delayed for at least 48 hours.

Engineers at NASA and Orbital Sciences, which built the rocket, were investigating the problem.

The mission's goal was to demonstrate the benefits of a group of small, low-cost satellites simultaneously measuring the earth's magnetic fields from different locations.

The ST5 project is part of NASA's New Millennium Program, which was created to identify, build and test innovative technologies for use in future missions.