WASHINGTON — SpaceX launched the final 10 Iridium Next satellites into orbit Jan. 11, completing its first mission of the year and the last in a multi-launch contract for its largest non-government customer, Iridium Communications.

The SpaceX Falcon 9 rocket took off at 10:31 a.m. Eastern from Vandenberg Air Force Base in California. Almost an hour later, Iridium’s new 860-kilogram satellites separated from the rocket one-by-one for 15 minutes. Iridium confirmed telemetry from all 10 satellites at 11:53 a.m. Eastern.

The launch completes the $3 billion Iridium Next constellation, which now numbers 75 satellites — 66 operational units and nine spares — in low Earth orbit. The second-generation satellites, built by Thales Alenia Space and integrated by Northrop Grumman Innovation Systems, replace Iridium’s legacy fleet from Motorola and Lockheed Martin that launched about 20 years ago.

SpaceX launched the Iridium Next satellites on a Falcon 9 with a first-stage booster that previously launched in September with Telesat’s communications satellite Telstar 18 Vantage.

SpaceX did not attempt to recover the payload fairings from this mission — something the company has often tried, so far unsuccessfully, to do during West Coast missions with the catcher ship Mr. Steven.

The Falcon 9 booster landed eight minutes after liftoff on the droneship “Just Read the Instructions,” in the Pacific Ocean.

The Jan. 11 launch completes a contract Iridium first signed with SpaceX in 2010 to orbit 72 Iridium Next satellites. At the time, Iridium and SpaceX expected the missions would take place from 2015 to 2017. Instead a combination of satellite production and launch delays pushed the first mission out to Jan. 14, 2017, and the last mission to today.

Iridium’s launch contract also evolved from the time it was signed. Matt Desch, Iridium’s chief executive, said Jan. 3 on a call with reporters that the original contract called for nine Iridium Next satellites per Falcon 9 rocket.

“After we found out that the Falcon 9 was going to be more powerful than expected, and would be able to launch 10 satellites with each launch, we downsized the contract to seven launches,” Desch said.

“These aren’t tiny satellites either,” he said. “Each satellite weighs about a ton, or approximately the size and weight of a Mini-Cooper automobile, so when you have 10 on one rocket it is a hefty payload.”

Iridium shifted the first two Iridium Next satellites to launch on a Russian-Ukrainian Dnepr rocket through Kosmotras, but had to cancel that mission because Russia did not provide regulatory approval.

Iridium then returned to SpaceX, splitting a Falcon 9 mission with NASA and the German Research Centre for Geosciences’ twin GRACE-FO science satellites. The recreated eighth launch — chronologically the sixth in Iridium’s launch order — carried five Iridium Next satellites, increasing the in-orbit constellation from 72 to 75.

Desch said the price of the contract stayed roughly the same despite the changes. When announced in 2010, SpaceX and Iridium said the launches were $492 million altogether.

Iridium is keeping another six spares on the ground, but Desch said the company would consider launching those as well should favorable rideshare opportunities appear.

Desch said six of the newest 10 satellites will serve as operational units, replacing legacy satellites about three weeks after launch. The other four will serve as in-orbit spares.

The completed constellation will enable Iridium’s new Certus products for improved L-band connectivity to boats, aircraft, and other end users. The launch also completes Aireon’s network of aircraft-tracking sensors, which are included as payloads onboard each Iridium Next satellite.

“[The launch] means our network will finally achieve the financial independence and the security that makes a satellite network operator mature and successful, and creates a lot of opportunities for us that we’ve never had before,” Desch said.