地基深空激光通信的多口径发射关键技术研究

There are many benefits of laser communication, including extremely wide bandwidth transmitters and receivers available for carrying high rate data, extremely high gain from small terminals. So many researchers are studying in this field for the increase in demand for long-haul communications services. It is required more power for deep space laser communication due to longer distance. And the influence of atmosphere is significant for ground-based terminals. Using multiple transmitters is a feasible scheme to increase the transmit power and decrease the atmospherically induced intensity modulation of the uplink beam. The transmitter system of the Lunar Lasercom Ground Terminal (LLGT) comprises four 15-cm co-boresighted telescopes on a single gimbal, which is the primary ground terminal for NASA’s Lunar Laser Communication Demonstration (LLCD). And it demonstrated the first time high-rate duplex laser communication between Earth and satellite in orbit around the Moon. Several technical problems were identified that prevented demonstration of the uplink and ranging in the Lunar Lasercom Optical Ground System (LLOGS), based on the OGS system with its 1-meter-diameter telescope, one of the alternate terminals. Mainly problem is the misalignment of transmitter with respect to the receiver and the differential misalignment between the three transmitters. In the project, the key technologies of using multiple transmitters are studied, including beam pointing alignment between transmitters and removing delays between transmitters. By learning the success of LLGT and the lessons of LLOGS, optics and mechanism system, hardware and software of control system are designed. Using our 1.2-meter-diameter telescope and bi-aperture 53cm telescope and participating the ground-satellite-ground demonstration project, experiment can be performed.

激光通信因其通信容量大、数据传输速率高、成本低、抗干扰性好、安全性高、设备小巧等特性成为了研究热点，也契合了日益增长的数据高速传输需求，深空通信由于距离较远，需要更大的激光发射功率，地基通信则受大气影响显著，多口径发射是一个可行的方案，美国月球激光通信演示系统（LLCD）的主站LLGT正是采用4个15cm口径发射的，成功实现了高速率的激光通信传输，而经过升级改造的备份站LLOGS则由于多口径发射的设计技术缺陷导致上行链路通信失败。本项目针对多口径发射，研究其关键技术，包括同光轴、同光程等，学习LLGT的成功经验和LLOGS的失败教训，设计相应的光机系统和控制软硬件系统，利用研究组已有的1.2米望远镜和双筒53cm望远镜试验平台以及参与的星地星激光通信演示系统项目，开展试验验证。

激光通信具有通信容量大、数据传输速率高、成本低、抗干扰性好、安全性好、设备小巧等特性成为了研究热点，也契合了日益增长的数据高速传输需求。目前，国内对地月深空激光通信技术的急迫需求，以及在该领域技术基础及其薄弱的状况。需开展深空激光通信的关键技术研究和试验验证工作。..本项目的演示试验的光学平台系统基于云南天文台的1.2m光学望远镜和53cm双筒望远镜，经过适应性升级改造构建。光学平台系统的升级改造内容包括：加装激光发射望远镜，确保发射激光束精确指向并覆盖目标卫星；改造望远镜捕获跟踪系统，确保主光学系统能够精确跟踪卫星，接收激光信号，并耦合给超导单光子探测器（此系统得到HGS激光通信项目的支持）。本项目中主要解决的是多口径光轴平行度问题。.1).多孔径组阵激光发射技术.对发射望远镜设计时充分计算，进行多姿态、多工况仿真，并采用了高刚度、低热胀材料，加大设计裕量等方法，在设计生产环节保证高性能；采用了快反镜、目标跟踪闭环技术，实时校正发射镜筒指向；观测时多频次进行同轴度校准，提高精度。通过这些有效技术措施，实现发射激光指向平行度。.2).精密跟踪技术.对目标的稳定跟踪是与目标建立稳定激光通信的前提，本项目完成了相机控制软件和快反镜控制软件的研发，实现了对目标的闭环精跟踪控制。相机控制软件具有相机控制、图像采集和显示、图像保存、图像处理识别星象和计算星象质心、计算脱靶量并通过网络广播等功能，通过与SExctracor软件的质心计算结果比对，脱靶量计算精度优于3μrad。快反镜控制软件具有基本快反镜控制、监听相机控制软件的脱靶量网络广播信息、闭环控制等功能。通过相机检测、快反镜调整的精跟踪系统闭环控制技术，满足激光通信对目标稳定跟踪的要求。.本项目研究过程中产生的多孔径组阵发射技术、精密跟踪技术等成果，可直接应用于其它空间激光通信项目的地面站光学系统建设。