Laser Interferometer Space Antenna (LISA) (IMAGE) NASA/Goddard Space Flight Center Caption The Laser Interferometer Space Antenna consists of three spacecraft orbiting the sun in a triangular configuration, separated from each other by five million kilometers. Each spacecraft will contain freely falling "proof masses" protected from all other forces except for gravity. The relative motion of the masses can be measured by combining laser beams shining between the spacecraft. Passing gravitational waves will ripple space and time, revealing their presence by altering the motion of the proof masses. Click image to view animation of LISA directly detecting the "tremors of space." Credit NASA Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.