SpaceX, the space launch provider founded by Elon Musk, took another significant step forward in its efforts to make its rockets truly reusable when it safely landed a first-stage rocket on a barge in the Atlantic, at the fifth attempt.
The landing on Friday on the barge follows the company's successful return of a first-stage rocket to land at Cape Canaveral, Florida, in December.
The launch marked SpaceX's first mission to send one of its Dragon supply craft to the International Space Station since last June, when one of its Falcon 9 rockets carrying supplies to the station exploded 45km above the Atlantic Ocean. The December event was a test return to flight following that explosion, the only complete failure of any Falcon 9 launch. The explosion resulted from the failure of a strut.
A video showed the first-stage rocket reappearing from the sky 300km north-east of Cape Canaveral, its engine burning, about eight minutes after take-off. It extended a set of landing legs and settled upright on the drone barge, which SpaceX had named Of Course I Still Love You.
"Falcon 9 first stage on our drone ship in the Atlantic after propelling the Dragon spacecraft to the Space Station," SpaceX wrote on Twitter.
Nasa, the US space agency, which paid for the mission, immediately congratulated SpaceX on the achievement.
"Congrats to the SpaceX team and Elon Musk!" it tweeted. "Way to stick the landing and send Dragon to the space station!"
SpaceX's efforts are one of several under way aimed at reusing space launch vehicles to bring costs down sharply. Blue Origin, the space company of Jeff Bezos, the Amazon founder, last November became the first company to recover a first-stage rocket when it landed a rocket back in Texas after a suborbital flight.
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Blue Origin is also developing reusable engines for the first stage for Vulcan, the new rocket being designed by United Launch Alliance, which handles all the US's national security launches.
SpaceX has persisted with attempts to make recoveries at sea, despite the substantial difficulties, because it entails a considerably shorter flight back to earth for the rocket than a return to Florida. That in turn means the rocket has more remaining fuel, which improves its chance of manoeuvring successfully on to the drone ship.
Gwynne Shotwell, SpaceX's chief operating officer, said last month that she expected reuse to cut the cost of launches with the Falcon 9 — already cheaper than ULA's alternatives — by as much as 30 per cent.
SpaceX's lower costs have made it a critical part of the US's space programme. It has been carrying cargo to the space station for Nasa, the US space administration, since 2010 under an arrangement designed to bring down costs. Last year it also won the right to compete for the most sensitive US national security launches, on which ULA had previously held a monopoly.
Previous attempts at landings at sea have failed either because of problems with the extending legs or because the rocket hit the barge at the wrong angle, causing it to topple over and explode.