https://www.theregister.co.uk/2018/05/22/spacex_to_send_grace_to_spaaaaace/

Because ride-sharing is caring, SpaceX will send the next batch of Iridium NEXT satellites into orbit along with a pair of NASA gravity monitoring orbiters, GRACE-FO.

The launch, scheduled for 1947 UTC (1247 PT) from California’s Vandenberg Air Force Base today, will reuse the outdated Falcon block 4 rocket that flung mystery-sat Zuma into orbit. Or didn’t, depending on which version of events you choose to accept.