In order to prove the final unproven piece of Einstein's General Theory of Relativity, NASA and the European Space Agency are going to shoot three spacecrafts to orbit around the sun to fire laser beams at each other. This is being done to detect gravitational waves, which is what Einstein's theory stipulates.
According to Einstein, when huge objects like black holes collide, gravitational waves - tiny ripples in time and space - would be generated. However, till now, they've been too weak to be measured, but the agencies now think that they've engineered a way around it.
There shall be gold platinum cubes on each ship and the lasers will measure the changes in the distance between them. The mission is expected to be launched in 2020.