A Russian rocket carrying a French satellite to test a German theory is scheduled for launch on Friday. At 21:02 GMT, the Soyuz rocket will blast off from Kourou, Europe’s spaceport in French Guiana, carrying the experiment.

Microscope, which stands for Micro-Satellite à traînée Compensée pour l’Observation du Principe d’Equivalence, is designed to test the very heart of Einstein’s 1915 theory of general relativity, which gives us our best description yet of gravity.

Known as the principle of equivalence, it is derived from Galileo’s 17th century experiment to drop different masses from a tower to show that both hit the ground at the same time. Why they should do this is a mystery, and many physicists feel it may only be approximately true.

So Microscope will measure the principle of equivalence 100 times more accurately than before. If it discovers a deviation it would be an event that would shake the foundations of physics. It would prove that relativity is not quite right, and that would open a path to a more precise theory of gravity.

The Soyuz rocket carrying Microscope will also place ESA’s Sentinel-1B satellite and three tiny student CubeSats in orbit. Sentinel-1B is part of the EU’s Copernicus Earth observation programme. It carries a radar capable of making images and joins a sister satellite, which is already in space.

The CubeSats are 10cm cubes designed and built by students. Each tests a new satellite sub-system such as communications or attitude control. ESA’s Education and Knowledge Management Office sponsors the students to give them experience of working on real space missions while still at university.