HOUSTON — Endeavour’s crew unloaded the first of their primary payloads, the spare parts-laden Express Logistics Carrier-3, onto the International Space Station on May 18, shortly after shuttle commander Mark Kelly maneuvered the 247,000-lb. orbiter to a smooth docking.

The ELC-3 operations, methodically completed at 12:09 p.m., within 6 hr. of the docking, cleared the way for a similar transfer of the $2 billion Alpha Magnetic Spectrometer from Endeavour’s cargo bay to the station’s starboard solar power truss early on May 19.

Kelly brought the two spacecraft together at 6:14 a.m. EDT as they sailed on a northeasterly trajectory, 220 mi. over the Pacific Ocean, just east of Chile. The velocity vector docking followed a smoothly executed backflip by Kelly with Endeavour 600 ft. below the orbiting science lab. The slow somersault enabled astronauts aboard the station to photograph Endeavour’s underside heat shielding with long-lens cameras to complete the post-launch imagery collection of the shuttle’s thermal protection system.

“The entire rendezvous, approach and final docking was silky smooth,” said Gary Horlacher, NASA shuttle lead flight director, during a news briefing.

Meanwhile, LeRoy Cain, NASA’s Mission Management Team (MMT) chairman, says imagery analysts are studying three areas of tile damage under Endeavour’s right wing; those assessments should be complete within the next 48 hours. The areas include a site between the right landing gear door and external tank fuel line access door; a site on the right main landing gear door and a site on the right elevon hinge line.

The MMT may choose to assign the shuttle crew a more detailed inspection of one or more of the sites on May 21, Cain says. In all, imagery from tracking cameras and the May 18 docking revealed seven sites with tile damage under the left and right wings; only three were deemed to merit further analysis.

“We don’t have any reason for concern or alarm,” Cain told a news briefing. “These are areas we don’t have enough data, or analysis or photography yet to determine whether there is more assessment that we need.”

Endeavour will park at the station for 12 days of cargo exchanges and spacewalk maintenance.

Soon after hatches between the two spacecraft opened, Endeavour’s Roberto Vittori and Mike Fincke hoisted the 15,000-lb. ELC-3 from the payload bay and handed it off to the station’s robot arm — operated by shuttle pilot Greg Johnson and mission specialist Greg Chamitoff. Johnson and Chamitoff guided the platform to the station’s port-side solar truss for installation.

The ELC’s cargo includes a pair of ammonia coolant tanks for the station’s thermal control system, an oxygen tank for the airlock, a pair of S-band communications antennas, external circuit breakers and a spare arm for Canada’s mobile Dextre robot.

In all, four ELCs have been staged on the orbital outpost with heavy or bulky spare parts since late 2009 to fortify the station for the post-shuttle era.

Endeavour’s rendezvous operations also permitted a successful data-gathering session for the Sensor Test for Orion Relative Navigation Risk Mitigation (Storrm) hardware developed by NASA and a Lockheed Martin/Ball Aerospace Technology Corp. team for Orion spacecraft autonomous docking operations.