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Dragon's return trip
SpaceX’s robotic Dragon cargo capsule backs away from the International Space Station after its release by the station’s robotic arm. (NASA TV)

SpaceX’s robotic Dragon capsule was set loose from the International Space Station today and returned to Earth with more than 3,800 pounds of cargo and experiments, including a set of live mice that will be studied after their stint in zero gravity.

The trip marked the completion of SpaceX’s 12th space station resupply mission under the terms of its multibillion-dollar contract with NASA. “Godspeed, Dragon 12,” Italian astronaut Paolo Nespoli said as the Dragon was released by the station’s robotic arm.

Dragon’s parachute-assisted Pacific Ocean splashdown came five and a half hours later, at around 7:15 a.m. PT off the coast of Southern California. A recovery ship was sent to pick up the capsule and bring it back to Long Beach for shipment to SpaceX’s processing facility in Texas. The mice and other time-sensitive payloads will be delivered to NASA on an expedited basis.

The Rodent Research-9 study is aimed at investigating how extended periods of weightlessness affects blood vessels in the brain and the eyes, as well as tracking cartilage loss in hip and knee joints. The results could help scientists figure out new ways to help astronauts cope with the health effects of zero-G, and help arthritis patients back on Earth.

The habitat containing the mice was shipped up to the space station aboard the Dragon a little more than a month ago, along with a prototype supercomputer and more than three tons of other experiments and supplies. The supercomputer is staying in space, but today the Dragon brought back other scientific samples – including lung tissue that was grown in space and protein crystals that are thought to play a role in Parkinson’s disease.

The research facilities working on the experiments – including the Michael J. Fox Foundation, which is supporting the Parkinson’s disease research – will be looking forward to follow-up studies on the samples. Unfortunately, the mice don’t have as much to look forward to. Once they’re brought to the lab, they’ll be euthanized and dissected for study.

SpaceX’s Dragon is currently the only space vehicle capable of bringing substantial shipments back to Earth from the space station. Other robotic cargo craft, such as Russia’s Progress and Orbital ATK’s Cygnus, burn up during atmospheric re-entry. Russia’s crewed Soyuz spacecraft can bring people back from space, but there’s not much extra room for cargo.

That situation is expected to change within the next few years, when Boeing’s crewed Starliner space capsule and Sierra Nevada Corp.’s robotic Dream Chaser space plane enter service.

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