WASHINGTON — SpaceX and mobile satellite services provider Iridium, now halfway through deploying the Iridium Next constellation, are preparing for their fifth mission on March 18 from Vandenberg Air Force Base in California.

The Falcon 9 launch is expected to kick off a “rapid-cadence launch schedule targeting completion of the Iridium manifest by mid-2018,” according to a Jan. 22 Iridium statement.

Iridium CEO Matt Desch told SpaceNews by email that the rapid cadence equates to “an average of about 5 weeks between launches to ensure we complete launch 8 mid-year.”

Following the March 18 mission, the sixth Iridium Next launch is scheduled for mid-to-late April.

Like Iridium’s last SpaceX mission, the March launch will employ a booster that previously carried 10 Iridium Next satellites into low Earth orbit. SpaceX will use the same first stage as its third Iridium Next launch in October.

Iridium switched its fourth and fifth launches from new to pre-flown Falcon 9s in order to preserve the operator’s deployment schedule.

“We are entering the home stretch,” Desch said in a press release. “This is going to be a monumental year for us as we complete our constellation refresh.”

All 10 satellites in the fifth mission will form part of the active constellation following testing and validation. Iridium Next consists of 66 active satellites, nine in-orbit spares and six ground spares. French satellite manufacturer Thales Alenia Space is building the 81 satellites, with U.S. satellite builder Orbital ATK assembling, integrating, and testing each spacecraft at its manufacturing facility in Gilbert, Arizona.

The sixth Iridium Next launch will share a Falcon 9 with GRACE-FO, two research satellites for NASA and the German Research Center for Geosciences’ (GFZ) Gravity Recovery and Climate Experiment Follow-On mission. Iridium ordered that launch in February 2017 to fill in for a Dnepr mission that fell years behind schedule in a Russian regulatory quagmire. The change in plans increased the number of orbital spares from six to nine.

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...