In the first of two rapid-fire launches, a SpaceX Falcon 9 rocket blasted off from California and lifted 10 Iridium NEXT telephone relay stations into space early Monday, the California rocket builder's 14th launch so far this year and its third for the satellite telephone operator.
In what has become a routine, if still exciting milestone, the first stage of the Falcon 9 booster executed an automated return to Earth, landing with pinpoint precision on an off-shore droneship to chalk up SpaceX's 17th successful recovery in 22 attempts.
But the landing was, as always, a secondary objective. The primary goal of the mission was to launch the third set of 10 Iridium NEXT spacecraft under contracts with the satellite telephone provider to deploy 75 of the 81 relay stations being built to replace the company's current fleet of aging first-generation spacecraft.
Iridium's customers rely on 66 satellites operating in six orbital planes to make and receive calls anywhere in the world. The company's original block 1 satellites are being replaced by 66 Iridium NEXT spacecraft. Nine more will serve as in-orbit spares and another six will be held on the ground for launch as needed.
With a successful launch Monday, SpaceX will turn its attention to preparing another Falcon 9, this one featuring a previously flown first stage, for launch from the Kennedy Space Center Wednesday evening to boost an SES/EchoStar communications satellite into orbit.
This week marks the second time this year SpaceX has attempted to launch two missions within three days.
Monday's flight got underway at 5:37 a.m. PDT (GMT-7; 8:37 a.m. EDT) when the Falcon 9's nine Merlin 1D first-stage engines ignited, quickly throttling up and generating 1.7 million pounds of thrust. An instant later, the booster was released from pad 4E to begin its climb to space.
Arcing away to the south over the Pacific Ocean, the first stage engines burned for about two minutes and 23 seconds to propel the vehicle out of the thick lower atmosphere. The engines then shut down and the stage fell away to begin its descent to the droneship "Just Read the Instructions." The second stage's single engine then ignited to continue the push to space.
The first stage, meanwhile, fired three of its engines to help the booster reverse course followed a few minutes later by another three-engine firing to slow down for re-entry into the lower atmosphere.
Two minutes after that, a single engine ignited as planned, four landing legs deployed and the booster settled to a touchdown on the SpaceX droneship.
It was the 17th successful booster landing in 22 attempts, the tenth on a droneship and the 14th successful recovery in a row. Recovering the boosters is a key element in SpaceX founder Elon Musk's attempt to reduce launch costs by refurbishing and re-flying major rocket components.
About a minute and a half after the first stage landing, the Falcon 9's second stage engine shut down as planned. The vehicle was programmed to coast for the next 43 minutes before re-igniting for a short three-second burn to complete the launch phase of the mission, putting the vehicle in a circular 388-mile-high orbit.
Five minutes later, the Iridium NEXT satellites were expected to be released one at a time from a dispenser atop the second stage.
Each satellite in the constellation is able to communicate with up to four others -- one ahead, one behind and one to either side in adjacent orbital planes -- to provide a global network that services hand-held phones, machine-to-machine devices and ship- and aircraft-born data transmitters.
Designed by the European aerospace giant Thales Alenia Space and built by Orbital ATK in Arizona, each of the 1,896-pound solar-powered satellites features a phased-array antenna that can generate 48 beams over a footprint 3,000 miles across.
Each satellite also is equipped with high-speed links to ground stations and the required satellite-to-satellite cross links that enable a globe-spanning communications network.
The new spacecraft carry equipment provided by Harris Corp. to track ships at sea on a minute-by-minute basis and another Harris-built device, provided by a multi-agency consortium known as Aireon, that can track aircraft anywhere in the world.