Control system design and verification for inner-formation gravity measurement satellite system

Inner-Formation Gravity Measurement Satellite System (IFGMSS) is an original and innovative scheme for Earth gravity measurement. To achieve high precision Earth gravity mapping, outer satellite in IFGMSS should track the motion of inner satellite tightly and avoid the possible collision between them. To restrain the atmospheric drag effects and achieve the high precision relative position keeping, this paper presents an effective control method and a hardware-in-loop simulation system for IFGMSS. In the control algorithm, the compensation term of atmospheric drag with an exponent atmosphere density model is added. Considering the dynamic effects and uncertainty of real atmospheric drag, a PD-like control term is also introduced in the control algorithm. Since IFGMSS adopts micro-thrusters sets as the actuators, a modulation method is used to map the discrete impulse thrust into equivalent continuous thrust. In the hardware-in-loop simulation system, high-orders´ Earth gravity model and high precision atmospheric drag model are included, which can testify the controller effectively. A set of simulations are performed, and the results demonstrate that the controller are valid. It shows that the devised controller can effectively compensate each kind of disturbances and achieve mm-order´s high precision relative position keeping.