快响SAR卫星零多普勒波束中心姿态机动策略研究

Attitude maneuver strategy for zero Doppler beam center of fast response SAR satellite

传统偏航牵引方法采用惯性系下卫星轨道6要素推导得出姿态机动参数,在此方法中仅控制卫星主轴方向多普勒频率为0Hz,无法补偿SAR天线安装偏差和波束在天线内的方位距离向离轴角引起的斜距偏差和多普勒频率偏移,不能满足SAR系统时序设计需求和快响SAR卫星在轨实时处理器性能要求。因此,提出了地心固定坐标系中SAR天线波束指向零多普勒面内目标方向的姿态机动策略,使快响SAR卫星在轨实际波束中心多普勒频率为0Hz。该策略首先计算了基于场景目标的SAR总体设计的精确时序参数和观测参数,然后在地心固定坐标系中建立了波束中心多普勒频率为0Hz的SAR天线波束三轴指向模型,推导得出卫星三轴指向和姿态机动参数,并通过Matlab对该策略进行了仿真验证。结果表明,该策略可将多普勒频率由地球自转引起的29kHz、天线与卫星安装偏差引起的360Hz和波束方位向离轴角引起的3 950Hz补偿至0Hz,同时将由天线与卫星安装偏差和波束距离向离轴角综合引起的波束中心偏离目标的斜距偏差6.28km补偿至米的量级。

The attitude maneuver parameter is derived from six elements of satellite orbit in ECI for traditional yaw-steering method.Only the Doppler centroid frequency of satellite main axis is compensated to zero.The error slant range and Doppler centroid frequency drift arose by the installation error between antenna and satellite and the beam angle departing from coordinate axis in elevation and azimuth direction are not removed.The requirements of SAR system time order and on-board real-time processor of response SAR satellite isn′t satisfied.A new strategy of SAR antenna beam to target in zeros-Doppler plane of ECF was proposed so that Doppler frequency of beam center for fast response SAR satellite would be zero.Firstly,the accurate time order and look parameter was computed.Secondly,satellite′s three axes direction was derived from SAR beam′s three axes direction in ECF.Finally,the attitude maneuver parameters were obtained.The simulation results by Matlab show that applying the strategy to the fast response SAR satellite,the Doppler frequency 29 kHz of earth rotation,360 Hz of installation error and 3 950 Hz of the beam departing angle are compensated to 0 Hz.Simultaneously the slant error 6.28 km is compensated to meter level.