Endeavour heads back to station for sensor test

A test of a new sensor system is under way as Endeavour begins a close approach with the International Space Station it departed about three hours ago.

Trailing the station by about four miles, Endeavour fired braking thrusters around 2:40 a.m. EDT to slow its backward trajectory.

At a distance of 30,000 feet, shuttle commander Mark Kelly at 3:01 a.m. executed another burn to push Endeavour back toward the orbiting science complex for a "re-rendezvous."

The experiment called STORRM will test visual navigation sensors and a high-definition docking camera in development for future spacecraft based on Orion, which was begun under NASA's Constellation program and will be modified for a new exploration program.

STORRM is an acronym for Sensor Test for Orion Relative Navigation Risk Mitigation.

The system bounces pulses of light against reflectors that were installed on the station's shuttle docking port during an April 2010 shuttle mission.

Sensors convert the data into real-time 3-D images with a resolution up to 16 times higher than current shuttle sensors.

The sensors can provide data from as far as three miles away -- three times the shuttle's range. They're also five times lighter and use five times less energy, according to developer Ball Aerospace Corp.

Endeavour will climb up to within 300 behind and 1,000 below the station before completing the test and separating from the outpost for good.