The Falcon 9 first stage used on the launch of a Dragon cargo spacecraft to the International Space Station was meant to land at the company's Landing Zone 1 at Cape Canaveral, several kilometers to the south of Space Launch Complex 40, where the rocket lifted off.
The Dragon cargo capsule is carrying an in-space refueling experiment, a new carbon-monitoring sensor for the station, and supplies for the six astronauts aboard the orbiting lab, three of whom just arrived after launching aboard a Russian rocket.
The Falcon 9 booster splashed into the water some 2 miles (3 km) off the coast from the SpaceX landing zone.
A stalled hydraulic pump for one of the booster's grid fins caused it to enter into a rapid spin on its return flight.
SpaceX chief Elon Musk said the booster appeared to be undamaged. "We will show all footage, good or bad", he added.
If that first test of the unpiloted SpaceX Falcon 9 rocket and Crew Dragon spacecraft goes well, a second test will fly astronauts Robert Behnken and Douglas Hurley to the International Space Station in June. "Recovery ship dispatched", Musk tweeted. It is unknown, however, whether this particular rocket will be certified for another launch, due to possible damage from contact with salt water.
The mission had been a complete success until the aborted landing.
Musk has the Pentagon beat when it comes to euphemisms, though. That Falcon 9, he noted, won't attempt a landing, since it needs the booster performance that would be reserved for a landing to carry out the mission.
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It's unclear exactly how the first stage stopped its roll, Hans Koenigsmann, SpaceX vice president of build and flight reliability, said during a postlaunch news conference today.
"It's really wonderful how it stopped rotating at the very end as the landing legs come out", Koenigsmann said. The stage, at one point spinning rapidly, ended up touching down on the surface of the ocean a few kilometers offshore. "Even if it is on land it avoids buildings".
In addition, Koenigsmann said, Falcon 9 first and second stages both feature autonomous "flight termination systems", which would step in if the above safeguards somehow fell short.
If the booster had veered off-course more than two minutes before landing, Gebhardt said, then it would have exploded. "So it stays away from populations and property, and ensures public safety".
This marks SpaceX's 16th mission to the International Space Station.