WASHINGTON — SpaceX has set May 19 as the launch date for a Falcon 9 mission that will carry satellites for commercial fleet operator Iridium and a joint mission for NASA and Germany, according to Iridium.

The mission is scheduled to launch from Vandenberg Air Force Base in California, delivering the twin GRACE-FO, or Gravity Recovery and Climate Experiment Follow-On satellites, to low Earth orbit, followed by five Iridium Next satellites.

The Falcon 9 launch replaces two Dnepr missions after the Russian-Ukrainian company Kosmotras stopped launching the rocket in 2015. Iridium said Russian regulatory approvals prevented its mission, which was supposed to orbit two Iridium Next satellites ahead of the rest of the constellation.

Despite being the eighth Falcon 9 launch Iridium ordered from SpaceX, the shared Iridium Next and GRACE-FO mission will be the sixth in Iridium’s constellation deployment. In an April 9 release, Iridium said the May 19 launch “maintains scheduled completion of the Iridium NEXT manifest in 2018.”

Iridium procured the shared launch in January 2017, seven years after signing an earlier contract to launch 70 Iridium Next satellites on Falcon rockets in groups of 10 each. The company has 50 Iridium Next satellites in orbit, and another 25 awaiting launch.

Iridium said its next five satellites ship to Vandenberg this week where they will join the GRACE-FO satellites.

Two more Falcon 9 launches of 10 satellites each will complete Iridium’s fleet refresh. The final constellation is to consist of 66 active satellites, nine in-orbit spares and six ground spares.

European manufacturer Thales Alenia Space is building the satellites and integrating them at Orbital ATK’s Arizona factory.

GRACE-FO is a joint project of NASA and the German Research Centre for Geosciences (GFZ). It succeeds the original GRACE mission that launched in 2002 to map the Earth’s gravity field, providing information about the movement of mass in and around the Earth.