NASA and the German Research Centre for Geosciences (GFZ) say they are on track to launch a pair of Earth-observing satellites May 22 aboard a SpaceX Falcon 9 rocket from Vandenberg Air Force Base in California.
Built by Airbus Defence and Space in Germany, the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites are set to lift off at 12:47 p.m. Pacific time.
Air Force Capt. Jennifer Haden, a weather officer at Vandenberg, said at a media briefing May 21 that there is "a less than 10 percent chance that weather conditions will be a factor at takeoff" on May 22. The backup launch date is May 23.
From an altitude of about 305 miles, the GRACE-FO satellites will monitor variations in Earth’s gravitational pull to detect changes in the planet’s water bodies, such as glaciers, ice sheets, sea levels and underground aquifers.
To measure gravity, the identical, sports car-sized satellites will track small changes in the distance between them. While they will use a microwave-based system to measure that distance, they will test an experimental laser instrument that could be used on future missions to provide more precise data.
The GRACE-FO satellites will replace the two original GRACE spacecraft, which orbited Earth from 2002 to 2017.
NASA is spending about $430 million on the GRACE-FO mission, while GFZ is chipping in the equivalent of about $91 million.
The GRACE-FO satellites will share their ride into space with five Iridium [IRDM] NEXT communication satellites. The GRACE-FO twins arrived at Vandenberg in December and were stacked atop the Iridium spacecraft.
The liftoff is slated to occur a day after Orbital ATK [OA] launched its ninth cargo mission to the International Space Station for NASA. An Orbital ATK Antares rocket lifted off May 21 at 4:44 a.m. Eastern time from NASA’s Wallops Flight Facility in Virginia, and its Cygnus spacecraft is scheduled to reach the station May 24.