https://www.cnet.com/news/used-spacex-falcon-9-to-act-as-space-uber-for-nasa-grace-fo-iridium/ > The rare ride-sharing arrangement will carry five of Iridium's next-generation satellites and the twin spacecraft that make up the GRACE Follow-On (FO) mission for NASA and the German Research Centre for Geosciences (GFZ).  > The original GRACE (Gravity Recovery and Climate Experiment) mission observed the movement of water around the planet. GRACE-FO will continue that work by tracking movement of water and other types of mass on Earth, gathering data that can monitor changes in ice sheets, glaciers, underground water stores, lakes, rivers and oceans. The two Earth-watching satellites will also test new technology that uses laser to measure the distance between them rather than microwaves.