The launch of the third official cargo delivery mission by SpaceX to the station had been delayed from last month and again from Monday due to technical problems.
The rocket, carrying a Dragon space capsule loaded with 3,500 pounds of supplies for the space station, lifted off at just after 3:25 p.m. EST. The Dragon spacecraft reached the precise orbit needed to rendezvous with the space station on Sunday.
The mission was the first successful test of a new capability for the first stage of the Falcon 9: the ability to descend to a soft touchdown after delivering its payload to orbit. Conventional rocket boosters fall back to Earth after expending their fuel, reentering the atmosphere fast enough to disintegrate in the heat caused by friction with the air. This adds greatly to launch costs, which can top $200 million per launch, since a new rocket has to be built for each flight (see “SpaceX to Launch World’s First Reusable Rocket”).
SpaceX is already the lowest-cost provider of launch services to the U.S. government and the commercial satellite industry, with flights costing less than $100 million. The company hopes to drop costs even further with reusable rockets. SpaceX has been testing a Falcon 9 first stage in low-altitude hops at its McGregor, Texas, rocket development and testing center. The company posted a video of a test flight that took place last week with the same type of landing legs used on Friday’s orbital flight.
A camera on the second stage of the rocket captured live video of the nine SpaceX-built Merlin engines firing on the first stage of the rocket, with the plume of flame and smoke gradually expanding as the air around the vehicle thinned. At about 50 miles in altitude, and traveling at about 10 times the speed of sound some 35 miles off the Florida coast, the first-stage engines cut off as planned. As the first stage dropped away, the single Merlin engine in the second stage fired to propel the Dragon craft the rest of the way into orbit. Another camera view showed the Dragon moving away from the second stage into space with the Earth as a backdrop.
Meanwhile, a data link with the first stage confirmed that three of the nine engines on the first stage had fired as planned to slow the booster’s reëntry into the atmosphere. The plan then called for a single engine to restart at lower altitude over the Atlantic Ocean to enable a gentle splashdown. The second stage of the rocket was not designed to be recovered.
At a press conference about an hour and a half after the launch, SpaceX CEO Elon Musk confirmed that the initial data from the first-stage booster looked good. The booster had slowed to just over the speed of sound and had descended to about five miles, or about the altitude of a commercial airliner, before the terrestrial tracking station lost contact.
The latest data showed that the vehicle was not rolling. During the first attempt of a Falcon 9 first stage to safely splash down following an orbital flight, in November, the rocket spun out of control. Along with the addition of landing legs, the booster used for Friday’s flight included more powerful thrusters for countering the booster’s rolling motion.
Even so, Musk was not initially confident that the booster had landed softly on the water because of high waves.
“I think it’s unlikely that the rocket was able to splash down successfully,” he said during the post-flight press conference. At the time of the conference, he and his engineers were awaiting data from an airplane tracking the booster near the planned splashdown location, some 400 to 500 miles from Cape Canaveral. Boats that were to retrieve the booster were not able to approach the splashdown site because of the waves, which topped 15 to 20 feet.
However, Musk reported via Twitter about two hours after the press conference that the booster had indeed landed safely. “Data upload from tracking plane shows landing in Atlantic was good!” he tweeted. “Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal.” At last report, the crews of several boats were attempting to retrieve the booster.
SpaceX engineers are working toward the day when a Falcon 9 first stage will touch down on land. The company will attempt a touchdown on land after it demonstrates further precision splashdowns. The next big milestone following the successful recovery of a booster will be to reuse one, which could happen as early as next near. The company’s goal is not only to recover and reuse boosters, but to do so economically.
“The reuse must be both rapid and complete,” said Musk in the press conference, “like an aircraft or a car or something like that. If you have to disassemble and reassemble a car and change a bunch of parts in between driving it, it would make it quite expensive. So it’s true that we don’t just have to recover it, we have to show that it can be reflown quickly and easily with the only thing changing being reloading propellant.”
The Dragon that launched on Friday’s flight reached Space Station and was grappled by the station’s robotic arm on Sunday morning. It was then installed at the Earth-facing port on the station’s Harmony module.
This was the fifth flight of a Dragon spacecraft. SpaceX has a contract with NASA for nine more cargo deliveries to the International Space Station. The company plans 10 more flights this year, including commercial satellite launches, each one of which will offer an opportunity to recover a booster.
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