Two NASA satellites named “Tom and Jerry” are chasing each other in space
In 2002, twin satellites were launched into space as part of a German-American project named GRACE (Gravity Recovery And Climate Experiment). The satellites are used to investigate the Earth’s gravity field from a polar orbit at a height of approx. 500 kilometres.
The Grace twins circle the Earth at a distance of 220 kilometres from one another. Both satellites constantly and precisely measure the distance between them. The change in the distance in between them helps study the Earth’s shifting water masses and map their effects on the planet’s gravity field.
GRACE has far exceeded its designed five-year lifespan. The GRACE spacecraft are expected to remain in a slowly decaying orbit until 2016. Its successor, GRACE Follow-On, is expected to launch in 2017.