Italian astronomers are hoping to test an aspect of Albert Einstein's theory of General Relativity - by using a disco ball in space.
The LARES (LAser Relativity Satellite) will be used to test for 'rotational frame-dragging'.
Large bodies such as the Earth pull on space-time as they rotate, a process called the Lense-Thirring effect.
It is thought this will effect smaller rotating bodies nearby causing them to precess.
The effect if very subtle however and very hard to measure. The difference in measurements being sought is as little as one part in a trillion.
LARES is about the size of a football but weighs nearly 400 kilos as it is made from super-dense tungsten.
If successful the mission will have cost a fraction of the cost of Nasa's ill-fated mission to look for the same effect.
Gravity Probe B cost $750 million and was beset by technical difficulties.
It has no moving parts but is covered in 92 reflectors. Lasers fired from Earth will bounce off these to measure its orbit.
Data will be combined with readings from two other satellites, LAGEO and LAGEO 2.