Feasibility For Testing Of The Equivalence Principle With Optical Readout In Space

The Equivalence Principle (EP) was raised by Einstein as a basic hypothesis of general relativity theory in 1907. However, the EP is not a universal principle of physics and many modern theories suggest the existence of new interactions which violate the EP. Therefore, the EP test is significant for verifying the Einstein's general relativity and searching for new interactions. The EP has been tested by many experiments in several parts in 1013, which are limited by the terrestrial environment noises. Many space projects, such as the STEP, GG, and MICROSCOPE missions, were proposed to test the EP at a higher level of 10-15～10-18. Recently, with the research and development of the LISA (Laser Interferometer Space Antenna) and LISA Pathfinder missions, the interferometer and charge management technologies are rapidly developed. Therefore, the TEPO (Testing of the Equivalence Principle with Optical readout in space) concept has been proposed to test the EP using these technologies.In the TEPO mission, the two concentric test masses which made of different materials are set into the same orbit around the Earth. Their relative motions with respect to the spacecraft are monitored by the laser heterodyne interferometers in the sensitive axis and are monitored by the capacitance transducers along other directions, and then are controlled motionless with respect to the spacecraft by the electrostatic actuators. The difference of the feedback electrostatic forces acting on the test masses along the sensitive axis implies the violation of the EP and is mearsured by the experiment. The key technologies of TEPO consist of the inertial sensor, the laser heterodyne interferometers, the ultraviolet discharge technique and drag-free control.In this paper, firstly, the feasibility of TEPO is discussed and the noises in the experiment are theoretically calculated in detail. Then, the requirements of the key techonologies are analyzed. The analysis shows that the accuracy of the TEPO is limited by the direct disturbance acting on the test masses and the noise induced by the inertial sensor. Finally, the accuracy of the TEPO based on the best level of the latest space technologies such as the heterodyne interferometer, inertial sensor, drag-free control and ultraviolet discharge technique is estimated and the result shows that the equivalence principle could be tested at 8×10-17 with one day integration.