As the Russian/Ukraine Dnepr and corresponding launch services can no longer be provided by the International Space Company Kosmotras (ISCK), the joint NASA-GFZ Joint Steering Group has decided to exchange the GRACE-FO launcher. The corresponding contract was signed on 14. November 2016 by the Board of GFZ and Iridium Satellite LLC. It stipulates a "Rideshare" between GRACE-FO and 5 Iridium-Next satellites on a Space-X Falcon-9 from Vandenberg Air Force Base in California within the launch period December 2017 till February 2018. This also includes a contract with Airbus D&S who will build the necessary Multi Satellite Dispenser and will perform the Launch Service Management under contract of GFZ. The GRACE-FO satellites will be launched into a co-planar orbit and following (GRACE-like) orbital parameters:
Further information can be found here.