WASHINGTON — Mobile satellite services provider Iridium will use previously flown Falcon 9 first stages for its next two launches in order not to miss its mid-2018 goal for completing the Iridium Next constellation.

The first Iridium mission with a previously flown Falcon 9 first stage will take place Dec. 22 from Vandenberg Air Force Base in California, according to an Iridium statement. That launch, its fourth with SpaceX overall, will be followed by the second pre-flown mission early next year.

That will leave just three launches for Iridium and SpaceX to complete by the middle of next year.

In an Oct. 19 tweet, Iridium chief executive Matt Desch said using previously flown boosters brings “more schedule certainty to complete 5 more launches over next 8 months.”

Previously, Desch said he was open to using pre-flown Falcon 9s if that would accelerate Iridium’s already delayed launch schedule. Now the goal is to avoid further schedule slippage.

In a statement, Iridium said the revised launch plan allows the company “to maintain its planned cadence of completing all launches by mid-2018, even with SpaceX’s busy launch manifest.”

Iridium had hoped to complete the Iridium Next constellation in 2017, but a combination of manufacturing setbacks with Thales Alenia Space, Russian red tape with the Kosmotras Dnepr rocket and two Falcon 9 explosions — one in 2015 and one in 2016 — pushed that schedule out to 2018. Those delays forced Iridium to get an extension on a $1.8 billion loan from French export-credit agency Coface for the satellites.

Iridium will save some money by switching to previously flown boosters for two of its five remaining Falcon 9 launches, but the company did not quantify the savings. “Cost is better, but not [the] driver,” Desch tweeted.

Iridium has launched three times this year with new Falcon 9 rockets each carrying 10 satellites. The next four Falcon 9 missions will also carry 10 satellites at a time, followed by a fifth Falcon 9 mission split between five Iridium Next satellites and two satellites for a joint NASA-Germany science mission.

“I believe that reusability is the future for satellite launches, and I think SpaceX has intelligently built their Falcon 9 program around this strategy,” Desch said in Iridium’s Oct. 19 statement. “With three successful flight-proven Falcon 9 launches already this year, we’re excited to show leadership towards the sustainable access to space, while also making sure we maintain our cadence to complete the five remaining Iridium NEXT launches by the middle of next year.”

Iridium said insurers are not hiking up premiums for the used booster launches, a vote of confidence “that the risk profile is unchanged.”

Iridium is launching 75 of the 81 next-generation satellites it has on order. Sixty-six will be used for the active constellation with nine launched as in-orbit spares. The remaining six will be kept on the ground unless needed.

Caleb Henry is a former SpaceNews staff writer covering satellites, telecom and launch. He previously worked for Via Satellite and NewSpace Global.He earned a bachelor’s degree in political science along with a minor in astronomy from...