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SpaceX cargo ship delivers supplies to space station

A SpaceX Dragon cargo ship loaded with nearly 5,000 pounds of supplies and equipment, including a new docking mechanism needed by U.S. commercial crew ships, reached the International Space Station early Wednesday after a two-day orbital chase.

Approaching from directly below, the Dragon spacecraft pulled up to within about 30 feet of the lab complex and then stood by while Expedition 48 commander Jeff Williams and Kate Rubins, operating the station's robot arm, locked onto a grapple fixture at 6:56 a.m. EDT (GMT-4).

"We've captured us a Dragon," Williams radioed. "Congratulations to the entire team that put this thing together, launched it and successfully rendezvoused it to the International Space Station. We look forward to the work that it brings."

"Bravo zulu. That's Navy speak for well done," replied astronaut Victor Glover from mission control. "From a grateful ground team, we'd like to thank you for your hard work today and for all of your effort leading up to the capture. ... Now let's get this vehicle berthed."

Flight controllers at the Johnson Space Center in Houston then took over arm operations and pulled the Dragon in for berthing at the Earth-facing port of the forward Harmony module. Once properly aligned, 16 motorized bolts in the port's common berthing mechanism drove home to lock the spacecraft in place.

The crew plans to open hatches Thursday to begin unloading supplies and equipment packed in its pressurized cabin.

The Dragon was the second cargo ship to reach the station in just a day and a half. A Russian Progress freighter launched Saturday from the Baikonur Cosmodrome in Kazakhstan completed its own two-day rendezvous Monday night, docking at the Russian Pirs module.

A time exposure captures the SpaceX Falcon 9 launch Monday (left) and the return to Earth of the rocket's first stage (right) at the Cape Canaveral Air Force Station. SpaceX

The Dragon, boosted into orbit overnight Sunday by a SpaceX Falcon 9 rocket, is the ninth operational cargo flight launched by the California company under an initial $1.6 billion contract.

Packed in the spacecraft's pressurized cabin are 815 pounds of food, clothing and other crew supplies, 280 pounds of spacewalk equipment, including a refurbished spacesuit, 119 pounds of Russian hardware, 617 pounds of U.S. station equipment and spare parts and a full ton of research equipment and samples, including 12 mice.

Among the research gear is a compact device called a MinION that Rubins, a molecular biologist, will use to carry out the first gene sequencing in space. Other experiments will study bone and muscle loss in weightlessness and how beating heart cells are affected by the absence of gravity.

Mounted in the Dragon's unpressurized trunk section is Boeing-built International Docking Adapter, or IDA, the first of two NASA plans to attach to Harmony's forward and upper ports that will allow new crew ferry ships being built by Boeing and SpaceX to dock at the station starting next year.

The half-ton docking adapter will be pulled out of the Dragon's trunk by the station's robot arm on Aug. 16 and attached to Harmony's forward port Aug. 18 during a spacewalk by Williams and Rubins. The IDA replaces one that was destroyed in a June 2015 Falcon 9 launch failure. Another IDA will be launched in 2018 and attached to Harmony's upper port.

After Dragon's pressurized cargo is offloaded, the station crew will repack the spacecraft with frozen research samples, the 12 mice it carried into orbit, no-longer-needed equipment and hardware that needs refurbishment or repair, including one spacesuit.

All told, some 2,963 pounds of cargo will return to Earth when the Dragon departs the space station on Aug. 29.