He billed it as one of the "largest tech upgrades in history", telling investors he 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 fairing recovery ship "came very close but not quite", he said on SpaceX's webcast.
After release, the space-facing GRACE-FO satellite began pushing up into a higher, slower orbit, while the Earth-facing satellite started slipping down into a lower, faster orbit.More news: NOAA predicts near- or above-normal 2018 hurricane season
The communications satellites are part of Iridium's $3 billion effort to replace its entire globe-circling fleet with next-generation orbiters.
The planned GPS III launch "has slipped due to ongoing SpaceX qualification testing and final engineering reviews by both SpaceX and the Air Force of Falcon 9 design changes", the Air Force Space and Missile Systems Center said in a statement to Bloomberg News.
Although SpaceX will not seek to recover the first stage, it will attempt to recover one half of the rocket's payload fairing, using a system of on-board thrusters and parachutes to steer the fairing-half back to the Pacific Ocean toward a boat named Mr. Steven. The Falcon 9's first and second stages will separate seconds later. SpaceX's Falcon 9 rocket will tote two satellites that are part of NASA's Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, as well as five more Iridium Next communications satellites, when it takes off from Vandenberg Air Force Base in California at 3:47 p.m. EDT (1947 GMT). The May 22 launch grows the constellation to 55 Iridium Next satellites in orbit. Two more launches will increase the number to 75, including 66 operational satellites and nine spares. Second burn and Iridium orbit good....More news: Anger and red faces in South Korea over axed Trump-Kim summit
If you want to watch the launch live you can do so via the YouTube window embedded above.
This information is key for researchers studying the changes developing in glaciers, sea ice, ice sheets, oceans, lakes, and other bodies of water in solid or liquid form on Earth.
"GRACE was really a revolutionary mission for us understanding the water cycle and how the climate behaves and the trends which are taking place over the last 10 or 15 years", Frank Webb, GRACE-FO project scientist, told a pre-launch press conference.More news: Apple reportedly knew the iPhone 6 was bendier than previous models
The first-ever SpaceX launch from Vandenberg AFB Space Launch Complex-4 occurred on Sunday, Sept. 29, 2013. They will use microwave tracking that can measure the distance between the two 1,300-pound satellites to within the diameter of a red blood cell.