The Air Force Space and Missile Systems Center told Bloomberg News in a statement that the launch date "has slipped due to ongoing SpaceX qualification testing and final engineering reviews by both SpaceX and the Air Force of Falcon 9 design changes".
Today's launch will be the 56th for the Falcon 9 family, and the 10th launch of a Falcon 9 this year, if you include the debut of the Falcon Heavy.
Eleven minutes after launch, and shortly after first and second stage separation, the Falcon 9 rocket released NASA's twin GRACE-FO satellites.
One is a set of five Iridium communications satellites, the sixth mission that SpaceX has launched for the satellite operator as it replaces its entire fleet of spacecraft with 75 new models.
Meanwhile the SpaceX second-stage booster will fire until 11 minutes and 33 seconds into the flight, when NASA's GRACE-FO spacecraft will be deployed. In reality, the deployment of the two payloads will be separated not just by time but also by a burn of the Falcon 9's second stage engine to push it even farther away from Earth.
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The Falcon 9's first stage was previously used for a launch from Florida in January.
SpaceX's recovery ship, Mr Steven is heading out into the ocean to attempt to catch at least one half of the expensive shell used to protect spacecraft during the early phases of launch. Iridium shares rose more than 8 percent earlier Tuesday for the biggest intraday gain in nearly seven months. Two additional SpaceX flights are planned later this year.
The first-ever SpaceX launch from Vandenberg AFB Space Launch Complex-4 occurred on Sunday, Sept. 29, 2013. Desch expects the rest of the satellites to go up this year, "completing our Iridium NEXT constellation and starting on a well deserved [capital expenditures] holiday". The second package, consisting of a pair of satellites called Gravity Recovery and Climate Experiment Follow-On, or GRACE-FO, is a collaboration of NASA and the German Research Centre for Geosciences.
The GRACE-FO satellites were assembled by Airbus Defence and Space in Germany. The two satellites, about the size of a sports auto, will fly in tandem 137 miles apart in a 305-mile orbit around Earth's poles. The mission will measure changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. The satellites will be constantly measuring the distance between them by sending microwave signals back and forth.
"GRACE was really a revolutionary mission for us understanding the water cycle and how the climate behaves", said Frank Webb, GRACE-FO project scientist at the Jet Propulsion Laboratory, during a pre-launch briefing May 21.