WASHINGTON — The fourth SpaceX Falcon 9 mission for mobile satellite communications operator Iridium remains on track for Dec. 22, the company said today, assuaging concerns that the launch would be delayed along with other December missions.

The Dec. 22 mission from Vandenberg Air Force Base in California will be Iridium’s first to use a previously flown and refurbished Falcon 9 booster. Iridium said the booster will be the same one SpaceX used for a June Falcon 9 launch of 10 Iridium Next satellites.

“This will make Iridium the first company in history to reuse the same rocket,” Iridium said in a Nov. 28 press release.

Iridium has tapped SpaceX for eight Falcon 9 launches in total — seven with 10 satellites each and one split between five Iridium satellites and two NASA-Germany science satellites — as the company overhauls its 20-year-old low-Earth orbit constellation with new Iridium Next satellites. SpaceX’s current launch cadence puts the constellation’s completion date in mid-2018. Iridium switched its upcoming mission and the one to follow to reused Falcon 9s in order to maintain schedule.

SpaceX, which has already launched a personal-best of 16 times this year, still expects to notch at least 18 missions before January. In addition to the Iridium launch, SpaceX is slated to launch its thirteenth Commercial Resupply Services (CRS-13) mission to the International Space Station next month, although the launch has slipped at least four days to no earlier than Dec. 8, NASA said Nov. 22.

CRS-13 will be the first launch from Cape Canaveral’s Space Launch Complex 40 since a September 2016 pad explosion during preparations for a Falcon 9 static fire test that damaged the launch site.

SpaceX was scheduled to launch Zuma, a mysterious mission arranged by Northrop Grumman, in mid-November but postponed the launch due to concerns about Falcon 9’s payload fairing. No new launch date has been announced.

The debut of the Falcon Heavy rocket, previously targeted for December, could slip into January, SpaceX President and COO Gwynne Shotwell said in a recent SpaceNews interview.

“I don’t want to set a date for the Falcon Heavy launch,” she said. “We are going to static fire in December, see how things go, and then we will lift off as soon as we can thereafter. This will be the first time that all three cores are firing together, and we really want to make sure we do our due diligence.”

The 10 Iridium Next satellites for SpaceX’s Dec. 22 mission are “processing” at Vandenberg, Iridium said Nov. 28. Once in orbit, nine of the Next satellites will go into immediate service after testing and validation. The tenth, Iridium said, will travel for almost a year to another orbital plane where it will function as a backup. Iridium Next consists of 66 active satellites, nine in-orbit spares, and seven ground spares.

SpaceX and Iridium have a backup date for the fourth mission of Dec. 23.

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...