Research On The Preliminary Scheme Of Measuring The Newtonian Gravitational Constant G In Space

The Newtonian gravitational constant G is one of the most well-known physical constants in nature.Since the first G value obtained from Cavendish's torsion pendulum experiment in 1798,during the next 200 years,the experimental physicists around the world have continuously designed ingenious experiments,used updated device and improved experimental methods in order to measure G with higher precision.But unfortunately,its measurement precision is still the worst among all physical constants.In order to find the hidden systematic errors in the experiment,it is becoming more and more important to develop new methods for measuring this constant to obtain a more accurate G value and to clarify the differences in G values between different experiments.Benefiting from the direct exploration of cosmic space by humans in the past more than sixty years,basic physics has more experimental space for measuring weaker interaction forces(such as gravity),and we have the ability to launch artificial detectors into a vast space to perform the G measurement.The main work of this paper is research on the scheme of measuring the Newtonian gravitational constant G in space.The scheme is inspired by the classic gravity train mechanism.A small test mass is placed in a tunnel that passes through a larger source mass.Due to the spontaneous suspension of an object in space,the test mass will pass back and forth from the source mass under the influence of gravity.The G value can be derived from the natural frequency of the test mass.The experimental setup includes five objects: two solid silicon balls of equal mass with a cylindrical hole in the center;an aluminum alloy cylinder that connects the two solid balls;a smaller reflector,which will be placed inside the hole and move back and forth;a laser beam is used to measure the time of light to and from the reflector.We first use the Green function and Bessel function expansion methods to derive the analytical formula of the gravitational field of source mass,and obtain the distribution of the gravitational field inside the source mass channel,and determine the initial release conditions of the test mass.Secondly,the influences of geometrical metrology and mass distributions and the period of test mass for G measurement are evaluated,and the corresponding error budgets are given;finally,we evaluate the effect of the gravitational gradient effect of the system effect and the noise caused by the environmental magnetic field,cosmic rays,laser photon radiation pressure,residual gas impact,solar radiation pressure and so on.In the error budget,the geometric dimensions of the test mass and source mass are still the main error source.The final expected uncertainty of the measurement of the G value is better than 10 ppm.