Research On Theory And Method For Construction Of Inner Formation Flying Gravitational Reference Sensor

The implementation of space gravity detection missions such as satellite gravity measurement and spaceborne gravitational wave detection,depends on the elimination or precise measurement of non-gravitational disturbances.By constructing the purely gravitational orbit of the proof mass(PM),the inner-formation flying gravitational reference sensor(IFF-GRS)excludes the influence of non-gravitational forces effectively.The IFF-GRS,which is usually located around the mass center of spacecraft,consists of a cavity structure,displacement sensors mounted on the inner wall of the cavity,and a spherical PM contained within the cavity.It employs the relative displacement of the PM with respect to the cavity to drive the tracking control of spacecraft to the PM,then the purely gravitational orbit can be sustained.As no suspension control force is exerted on the PM,the IFF-GRS is more likely to reach a extremely low level of non-gravitational force.Thus it offers a perfect manner to construct purely gravitational orbit.Driven by the requirement of satellite gravity measurement,this dissertation has conducted a systematic rearch on the problems of relative measurement and sustain control confronted by the construction of the IFF-GRS.The main contents are given as follows:The major factors that influence the performance of the IFF-GRS are analyzed,and the model to break down the requirement of non-gravitational force exerted on the PM in frequency domain is established.Then the requirement breakdown for the IFF-GRS is carried out for the long-wave gravity field measurement mission(LWGFMM)based on absolute orbit perturbation and medium-high order gravity field measurement mission(MHOGFMM)based on long-baseline relative orbit perturbation.To meet the requirement of initial state capture of the PM and LWGFMM,The concept of optical power detection array based relative measurement system(OPDARMS)is proposed,which can reach a dynamic range comparable to the cavity gap on the magnitude of cm and a precision better than 1 mm.By extracting the center coordinate of the detectors that give effective output,the relative displacement determination algorithm is derived.The radiation pressure introduced by measuremet is analyzed in frequency domain,and the results show that for the working mode of emitting light periodically,the measurement disturbance is on the magnitude of 10-11m/s2/(?).An experimental system is established to test the performance of the OPDARMS prototype.The results show that within the relative motion space that centers around the nominal position of the PM and has a dynamic range no less than ±10 mm,the maximum positioning error using measurement output is 0.38 mm.To meet the requirement of mission data acquirement of MHOGFMM,the relative displacement measurement method based on optical shadow sensing(OSS)is adopted.Considering the sensor geometric layout,The relationship of sensor output and PM displacement is modeled.Two kinds of sensor layout,i.e.Three-Orthogonal and Two-Parallel,that can resolve the displacement f the PM analytically are designed.The constraints of major sensor design parameters are derived in view of measurement disturbance,sensitivity,and dynamic range.The noise floor of OSS is evaluated using electric shot noise,and the design parameters can reach a noise floor of 0.09nm/(?)are given.The error propation models for light spot variation,optical power fluctuation,beam divergence angle,beam center chatter and beam direction deviation are established respectively.The influence of spherical edge effect and beam diffraction effect on these models is analyzed,and the results show that the error prediction using the derived error propation models has an accuracy of higher than 19%.The OSS experimental system is established,and the experimental results show that a measurement error less than 1?m/(?)within the mission band of 5mHz?0.1Hz can be achieved.Taking into account of sphere manufacture error such as spherical surface variation and mass center offset to geometric center,the relative displacement determination method for the mass center of the PM using OSS information is studied.Based on the distance of mass center to spherical surface described by spherical harmonic series,the OSS signal model containing sphere errors is established.The mass center displacement determination method for the PM with approximately equal inerta is proposed based on frequency identification and measurement signal fit.To address the large state deviation just after the release of the PM,the mass center determination strategy for the entire control process is designed.Simulations are conducted to reveal the effectiveness of the method,and the results show that a mass center displacement determination precision on the magnitude of nm/(?)can be reached with the condition of OSS precision of 1nm/(?)and PM rotation frequency of about 10Hz.The influence of the spherical surface variation on the magnitude of 10 nm and mass center offset on the magnitude of 100 nm is highly eliminated.The mission capacity of the IFF-GRS supported by sustain control is evaluated.Considering the coupling between spacecraft and the PM,the dynamic model to describe inner formation flying is established.A roboust sustain control method based on H? loop shaping is proposed to meet the requirement of non-gravitational force supression and mass center displacement determination within the mission band.By combining the magnitude of residual non-gravitational force and measurement precision of relative displacement,the mission capacity supported by the IFF-GRS is analyzed.The concept of extensive application of the IFF-GRS on low-orbit navigation satellites is proposed,and the autonomous orbit prediction error accumulated due to residual non-gravitational force is analyzed.The results show that if the constant component of non-gravitational disturbance is suppressed greatly and a stochastic component on the level of 10-11 m/s2 is attained,the autonomous orbit prediction with m precision can last 3 month.The Simulations using a LQR controller reveal that the high performance IFF-GRS with a precision of nm can significantly reduce the sustain control requirement for power and fuel storage.