WASHINGTON — Mobile satellite services operator Iridium announced July 28 that SpaceX will conduct the third launch in its fleet replenishment Sept. 30 from Vandenberg Air Force Base in California.

Scheduled for 6:30 a.m. Pacific time, the launch will carry 10 Iridium Next satellites, bringing to 30 the number of satellites orbited for Iridium’s modernized constellation of low-Earth orbit telecommunications satellites.

SpaceX launched the first 10 Iridium Next satellites Jan. 14, followed by the second set of 10 on June 25. Iridium is launching its entire Next constellation on SpaceX Falcon 9 rockets, with completion expected in mid-2018.

Iridium had previously hoped to have the constellation in orbit this year, but SpaceX delays drew out that schedule, forcing the operator to request an extension on payments for the $1.8 billion loan it took out from French export-credit agency Coface for the satellites. French satellite manufacturer Thales Alenia Space is building the Iridium Next constellation with Orbital ATK assembling the satellites at its Gilbert, Arizona, factory as a subcontractor.

Iridium Chief Financial Officer Thomas Fitzpatrick said July 27 on a conference call with investors that Coface agreed to delay $98 million in payments until March 31, 2019, and that Thales agreed to defer $100 million in milestone payments to the first quarter of the same year. The agreement restricts how Iridium can use revenue gained from flight-tracking startup Aireon, which owes Iridium $200 million for carrying its hosted payloads on Iridium Next satellites.

SpaceX is launching 75 Iridium Next satellites, 66 of which will be active, and nine will be in-orbit spares (six ground spares brings Iridium’s total order to 81 satellites). SpaceX is launching the satellites 10 at a time for seven missions, plus a final mission with five Iridium Next satellites and two GRACE-FO, or Gravity Recovery and Climate Experiment Follow-On satellites, for NASA and Germany.

In the event of inclement weather, SpaceX and Iridium have a backup date of Oct. 1 for the upcoming launch. The mission will send all 10 satellites into the same plane around the Earth (the Iridium Next constellation is comprised of six planes with 11 satellites each).

The fourth Iridium Next launch is scheduled for November, Iridium said. Matthew Desch, Iridium CEO, said in June he would entertain using previously flown Falcon 9 boosters for 2018 missions if SpaceX could prove it would accelerate the launch rate for Iridium Next. Currently, all Iridium Next satellites are booked to launch on newly manufactured Falcon 9s.

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...