Research On Acquisition Pointing And Tracking Of Satellite Laser Communication Terminal

Satellite laser communication which use laser as carrier signal is an importantsatellite communication solution. It is a critical technology of space communicationnetwork, satellite-ground communication network.For the acquisition,pointing,tracking(APT) process of laser communication, such problems:predicting and searching for theobject terminal,image process for beam pointing angle recovery and robust control systemdesign were analyzed systematically and deeply in this dissertation.According to the process of establishing or keeping the laser communication link,thesubsystems of satellite communication terminal were introduced in detail. Basing on themechanic structure and optical scheme of canonical terminals,the work ?ow and taskof satellite laser communication terminal was divided into three partition.And then theconstraint factors for acquisition probability and the bit error rate with OOK, Manchesterand pulse position module were discussed.Considering the in?uence of satellite platform relative motion to communicationbeam and the beam transmit time because of long communication distance,coordinatetransform and Hill equation which usually describes the relative motion for two aircraft,were used to deduce the predicted pointing angle.And they were both verified in low orbitsatellites simulation.In the process of creating the communication link, scanning searchwas applied to capture the target terminal.The valid coverage factor and pre-overlappingfactor was proposed for coverage rate of projection beam. And then the least scanningpoint algorithm that can cover the uncertain area was induced based on the commonestscanning method.And the in?uence of valid coverage factor and pre-overlapping factorto acquisition time was analyzed. Simulation proves that entirely coverage and the leastscanning time problems can be resolved .The laser feedback loop offer the incident light from the joint terminal in anothersatellite.The terminal internal frame and fast steering mirror(FSM) frame were used todeduce the error angle of terminal antenna or FSM depending on spot center coordinate.The center coordinate calculated from gray image gathered by detector.And the imageinterfuses noise inevitably in the collection process,so the noise was divided into twocategories-isolated spot noise and stellar background noise in the light of noise area and power.Wavelet neural network filter and smoothing filter which connected with Sobeloperator and threshold method were proposed for isolated spot noise.Different from theisolated noise,the stellar background noise possess bigger area and energy, the selectionconnected region method and edge extraction were used for separating the valid spot andnoise spot.Through the combination of isolated noise filter and background noise filter,the simulation shows the gray image can offer better spot center coordinates.Moreover,the actuators for laser communication control system, brush-less directcurrent(BLDC) motor for terminal antenna loop and piezoelectric ceramics for FSM loop,were discussed. And the analysis result show the uncertainty of normal models.Whencontroller perturbation which caused by chip aging and analogical to digital convertererror appears, the analysis indicates that may arise some parameter variable.The inner andexternal disturbance were generalized for control system.And the in?uence of disturbanceto system task was simulated. Based on these points, robust H∞controller was designedfor terminal antenna loop and FSM loop which contains time delay unit.Simulation provedthat terminal antenna and FSM loop are robust for model perturbation and disturbance.Because the laser communication control system which composed by coarse loopand fine loop realizes APT process,the system stability become a focus.The whole APTsystem model was set up,and the stability condition was proposed under time delay systemstability theorem and matrix measure method. The design of terminal antenna and FSMloop was verified through the condition.In order to consummate the whole design process,common transform matrix was used to design the whole system stability.And then thecone complementary method transform the stability criterion to linear matrix inequalityconstraint.