Satellites prepare for hyper-accurate gravity measurement after SpaceX launch

SpaceX has launched two satellites that are capable of measuring their separation to within the width of a red blood cell, despite travelling at speeds of up to 7.5km per second.

The twin spacecraft from the Gravity Recovery and Climate Experiment Follow-On (Grace-Fo) mission will orbit 220km apart, tracking minute changes in the distance between them to measure fluctuations in the Earth’s gravitational pull.

The US-German mission launched on a SpaceX Falcon 9 rocket from Vandenberg Air Force Base in California yesterday, taking less than an hour to reach their near-polar orbits at altitudes of 409km.

Despite their incredible speed and the significant distance between them, on-board instruments will be able to measure their separation to about seven microns.

As changes in the distance reveal variations in the Earth’s gravity, that will allow scientists to track the movement of vast amounts of water on and beneath the surface.

“Grace-Fo will provide unique insights into how our complex planet operates,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate.

“Because the mission monitors many key aspects of the Earth’s water cycle, Grace-Fo data will be used throughout the world to improve people’s lives – from better predictions of drought impacts to higher-quality information on use and management of water from underground aquifers.” 

Built by Airbus Defence and Space in Friedrichshafen, Germany, the satellites will spend their first few days in space moving to the separation distance needed to perform the mission. With one slightly lower than the other, they will move apart until the leader is 200km in front. It will then move up into the same orbit.

Managers will then evaluate instruments and systems, before calibrating and aligning the spacecraft. After 85 days, they will start gathering and processing data, with the first release of results expected in about seven months.

The mission follows the US-German Grace project, which operated from 2002 to 2017. Among other things, the initiative was the first time scientists measured the amount of ice being lost from the Greenland and Antarctic ice sheets, and monitored the effects of earthquakes.