The International Space Station welcomed its first returning vehicle in years Monday — a SpaceX Dragon capsule making its second delivery.
Space shuttle Atlantis was the last repeat visitor six years ago. It's now a museum relic at NASA's Kennedy Space Center.
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NASA astronaut Jack Fischer noted "the special significance" of SpaceX's recycling effort as soon as he caught the Dragon supply ship with the station's big robot arm.
"That's right, it's flying its second mission," Fischer said. "We have a new generation of vehicles now led by commercial partners like SpaceX."
SpaceX is working to reuse as many parts of its rockets and spacecraft as possible to slash launch costs. The California-based company launched its first recycled booster with a satellite in March; another will fly in a few weeks.
The Dragon pulled up two days after launching from Florida. This same capsule dropped off a shipment in 2014. SpaceX refurbished it for an unprecedented second trip, keeping the hull, thrusters and most other parts but replacing the heat shield and parachutes.
Until their retirement in 2011, NASA's shuttles made multiple flights to the space station.
This new 6,000-pound shipment includes live lab animals: 40 mice, 400 adult fruit flies and 2,000 fruit fly eggs that should hatch any day. The mice are part of a bone loss study, while the flies are flying so researchers can study their hearts in weightlessness. Even more than mice and rats, the hearts of fruit flies are similar in many ways to the human heart, beating at about the same rate, for instance.
Some of these animals will return to Earth aboard the Dragon in about a month.
SpaceX officials anticipate using Dragon capsules as many as three times.
"It's starting to feel kinda normal to reuse rockets. Good. That's how it is for cars & airplanes and how it should be for rockets," SpaceX founder and chief executive Elon Musk said via Twitter following Saturday's liftoff of the Dragon and landing of the Falcon rocket's first stage.
Musk said the latest touchdown was "pretty much dead center" at the SpaceX landing zone at Cape Canaveral Air Force Station. Liftoff occurred next door at Kennedy Space Center.
The Dragon is the only station supply ship capable of returning items, like science samples. On Sunday, an Orbital ATK cargo ship named in honor of the late John Glenn departed the station. It will remain in orbit a week before burning up in the atmosphere upon re-entry. Glenn, the first American to orbit the world, died in December at age 95.
"Godspeed & fair winds S.S. John Glenn," Fischer wrote in a tweet.