Attitude Dynamics And Control Of Tethered Spacecraft With Artificial Gravity During Interplanetary Orbit Maneuver

In recent years,manned deep-space flight missions have been proposed with the development of aerospace technology.Compared with the mission in low-earth orbit,deep-space flight will have a long period of microgravity,which seriously harms the health of astronauts and directly affects the mission,besides,due to the busy schedule,astronauts in deep-space flight do not have much time to recover and have to fulfill their task immediately.The physical fitness of astronauts is the essential to deep-space manned missions.Traditional exercise training equipment is not enough to compensate for the long-term damage caused by microgravity.The idea of generating artificial gravity on spacecraft was put forward,which has become the research focus in the field of manned deep-space spacecraft.The proposal of tethered spacecraft provides a solution to artificial gravity.Tethered spacecraft has the advantage of larger radius of gyration which can generate sufficient centrifugal force to act as artificial gravity at a lower angular velocity.However,as a deep-space vehicle,it needs to consume a large amount of propellant in a short time in order to achieve the pulse during interplanetary orbit maneuver,resulting in the change of the mass distribution,so the original attitude balance will be broken,which will influence the pointing stability of thrust and cannot enter the prospective orbit.Obviously,this is not expected.This literature paper has deeply studied the attitude dynamics modeling and control of tethered spacecraft with artificial gravity in the process of interplanetary orbit maneuver,mainly including the following aspects:Aiming at dynamical modeling problem of tethered spacecraft with artificial gravity,this paper chose with offset thruster(that is,the thrust is not parallel and perpendicular to the tether)of the tethered spacecraft system;with the goal of pointing stability,we use Euler angle to construct spacecraft attitude dynamic equation which pivoting the axes paralleled with the needed velocity increment based on variable mass system dynamics.Then we get the equation of keeping pointing stability,which is the function of thrust?mass and angular velocity.According to the round-trip flight plan between Earth and Mars,we calculate the propellant consumption in the four times interplanetary orbit maneuver based on the tethered spacecraft.Then we set the artificial gravity level according the gravity in the surface of Earth and Mars.By the artificial gravity level,we calculate the needed angular velocity and thrust size.Including the influence of the thruster on and off,we calculate the mass equation which is needed to maintain the pointing stability.Then we get the initial attitude at startup of the thruster by substituting the attitude at the beginning of control section into the dynamics with mass equation.Finally,using the mass equation and the initial attitude,we have conducted a numerical simulation,which show that the tethered spacecraft can maintain the thrust pointing stability and the artificial gravity level.Finally,considering the possible interference of the thrust and initial attitude during orbit maneuver,we have analyzed the influence caused by the error of thrust and initial attitude and we find that pointing stability is seriously impressed by the initial attitude and slightly by the thrust.For unsteady state of initial attitude,we find a similar steady state;because the unknown moment of inertia for orbital maneuver has characteristic of fast time-varying,with the tracking target of ideally motions,adaptive back-stepping sliding mode controller is designed,which ensure the pointing stability of thrust during the interplanetary orbit maneuver for tethered spacecraft with artificial gravity.An adaptive robust sliding mode controller is designed for the unstable motion state and unknow moment of inertial after the end of maneuver,which realizes the system from unstable state to a stable state of pivoting around the principal axis of inertial and generates the expected artificial gravity.