SpaceX launches NASA satellites to track Earth's water cycle
Elon Musk-led SpaceX launched twin NASA satellites on Tuesday that would track the Earth's water movement and ice melt. The GRACE-FO satellites are at an 490-km altitude in a near-polar orbit, circling the Earth once every 90 minutes. The two satellites track movement of mass by measuring deviations caused in their 220-km separation with a hair-width accuracy by gravitational changes.