The full form of GRS is Gravitational Reference Sensor.

Dr. Ke-Xun Sun and Professor Byer at Stanford University have developed an all reflective grating based gravitational reference sensor. This invention provides a method with higher precision distance measurement and timing compared to existing capacitive sensing methods. Implementing the grating as a beam splitter results in reducing the background signal and consequently increasing the precision of distance measurement up to one millionth of an optical wavelength with low temperature effect. The information gathered through this measurement is transferred over a fiber optic waveguide without any additional optical elements in the path. This approach provides a precise measurement with high stability and geometric flexibility. This invention can be implemented in high precision semiconductor/ nanotechnology metrology tools. Another application for this invention is as a low cost approach to construct robust, inertial navigation service.