Updated 7:00 p.m. Eastern

PHOENIX — SpaceX successfully launched a Dragon cargo spacecraft to the International Space Station April 8 and landed the rocket’s first stage on a ship in the ocean after four previous unsuccessful attempts.

The SpaceX Falcon 9 lifted off on schedule at 4:43 p.m. Eastern time from Cape Canaveral, Florida, after a trouble-free countdown. The rocket’s second stage released the Dragon into low Earth orbit ten and a half minute after liftoff.

The rocket’s first stage, after separating from the second, performed a series of three burns to attempt a landing on a ship in the Atlantic Ocean downrange from the launch site. Video of the launch showed the stage landing on the ship eight and a half minutes after liftoff, to raucous cheers from SpaceX employees watching the launch at the company’s Hawthorne, California, headquarters.

SpaceX had made four previous efforts to land the stage on a ship, part of the company’s efforts to recover and eventually reuse the stage. On those previous attempts, the stage either crashed onto the desk of the ship or toppled over.

“The thing that was a little different about this mission on the rocket side was that the rocket landed instead of putting a hole in the ship or tipping over,” said Elon Musk, SpaceX chief executive, in a post-launch press conference April 8. He added that, prior to the launch, he and his team estimated they had two-to-one odds of making a successful landing on this mission.

Hans Koenigsmann, vice president of flight reliability at SpaceX, said at an April 7 prelaunch briefing at NASA’s Kennedy Space Center that the company had the option of trying to bring the stage all the way back to Cape Canaveral, similar to the successful landing the company performed on a December launch. They elected, though, to attempt another landing at sea.

Falcon 9 CRS-8 launch
A SpaceX Falcon 9 lifts off from Cape Canaveral, Florida, on April 8 carrying a Dragon spacecraft bound for the ISS. Credit: NASA TV

“On this particular flight, we decided we wanted to go to the drone ship and see if we can get a successful landing on the drone ship,” he said, in part because upcoming launches only have the option of a drone ship landing given the nature of their missions. “It’s a good opportunity for us to refine our drone ship landing capabilities.”

At the post-launch briefing, Musk said that crews would go over to the ship as soon as the vehicle was safe to weld the legs to the deck, preventing it from tipping over should winds increase or seas become rough. The drone ship is scheduled to return to port on April 10.

He said that the stage would then be placed on the launch pad in Florda — possibly Launch Complex 39A — for a series of static fire tests to determine its condition. If the stage is in good health, he said SpaceX will “probably” use the stage on another launch, perhaps as soon as June. “We think it be a paying customer, but we have to have some discussions,” Musk said of the launch of the reflown stage.

Dragon and future Falcon launches
The Dragon is carrying more than 3,100 kilograms of cargo for the station, including crew supplies, experiments and station hardware. The largest single payload, accounting for nearly half the cargo mass on this mission, is the Bigelow Expandable Activity Module (BEAM), a prototype expandable module developed by Bigelow Aerospace that will be installed on the station for testing.

The launch is the third this year for SpaceX, after launches of the Jason-3 ocean science satellite in January and the SES-9 communications satellite in March. SpaceX President Gwynne Shotwell said at the Satellite 2016 conference shortly after the SES-9 launch that the company planned up to 18 launches this year, including the long-delayed first launch of the Falcon Heavy.

Koenigsmann said at the pre-launch briefing that SpaceX will still aiming for that goal. “It is true that we have to pick up the pace, and we will pick up the pace,” he said. “We’re hoping that we’ll be able to launch basically every other week by the end of this year and then maybe even increase the pace.”

Dragon is scheduled to arrive at the station April 10, with berthing of the spacecraft with the station’s Harmony module is schedule for approximately 9:30 a.m. Eastern.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...