Significance Humans need to observe various targets, including space, air, ground, and sea targets. Space targets include satellites, space debris, ballistic missiles, and hypersonic vehicles. Air targets include aircraft, airships, and small craft. Ground and sea targets include surface ships and ground vehicles. The past 20 years have seen an average of 12 collisions between space debris and space payloads every year. In addition, foreign ships and aircraft frequently invade our territorial waters and airspace and repeatedly spy on the activities in our important places. Therefore, the detection, identification, early warning, interception, and even striking of these abovementioned targets are an important and urgent research topic presently.

Multidimensional detection based on combined polarization detection, spectrum detection, and other optical technologies can provide the shape, material, location, and other information of the target simultaneously, effectively improving the dimensions and accuracy of space target information. At the same time, with the help of space laser communication, massive information can be quickly and safely transmitted to orbiting satellites and management departments, which can provide the decision-making basis for further disposal in time.

Progress In terms of space target detection, the United States has the largest and highest level of space target detection systems, followed by Russia. Europe starts late, but their system has rapidly developed in recent years. China is the latest to start and mainly performs ground-based observations. However, in recent years, China has conducted space-based observation tests and devised various detection methods, including photoelectric observation, radar monitoring, radio detection, and other detection methods.

In multidimensional detection, polarization detection technology has the advantages of highlighting the target, penetrating smoke, and identifying the truth and falsehood of the target. Spectral detection technology can distinguish the physical characteristics of the target material. Intensity detection technology has high light energy utilization and resolution, but it also has its own weaknesses. The information obtained by intensity detection is less and easily disturbed by the environment. Moreover, loss of the receiving energy and decrease in imaging resolution can be introduced by polarization detection. Table 1 gives a comparison of the advantages and disadvantages of several detection technologies. Therefore, combining the three abovementioned detection methods to give full play to their own characteristics and advantages helps not only in overcoming the difficulties of space target detection but also in greatly improving the overall detection performance. Changchun University of Science and Technology conducted a multidimensional oil species differentiation test; the test results are shown in Figure 3.

The X2000 flight terminal was developed in the United States from the aspect of integrating detection, imaging, and communication. It can realize the functions of bidirectional communication, bidirectional laser ranging, and high-resolution imaging. The United States also proposed the ACLAIM scheme, in which the laser communication antenna and space camera sharing a front telescope and a detector array is employed as the acquisition and tracking system and an imaging receiver. In China, satellite payloads were developed toward the direction of multifunctionality and integration to increase the system function and reduce the volume, mass, and power consumption of the load. This study proposes a new scheme for space target detection and information transmission, which integrates the four functions of laser ranging, spectral polarization imaging, super-resolution imaging, and laser communication into one. The system design and development were performed. Figure 17 depicts the system composition.

Conclusions and Prospect In summary, we introduce herein the research status of the technology of multidimensional detection and laser communication integration for space objects and summarize the principle, characteristics, and application of the related technologies. The preliminary research results of our team in the related aspects are as follows: 1) for space object multidimensional detection, the detection mechanism is studied, and a large aperture and a wide field-of-view space-based telescope super-resolution imaging optical system is designed; 2) a prototype of simultaneous and time-sharing polarization imaging detection for complex space targets is developed; 3) ground and sea surface tests are conducted. As regards space laser communication, the optical principle of one-point to multipoint simultaneous space laser communication is proposed for the first time by our team at home and abroad. Accordingly, a principal prototype is developed and a demonstration test is performed. For detection and communication integration, the urgent need for this space security technology is expounded, and the system design idea and a specific implementation scheme are given.

Our country should further perform an in-depth research on ultra-high-resolution imaging, full-polarization and hyperspectral multidimensional detection, space- and ground-based combined optical detection, multi-to-multi space laser communication, and integrated laser and microwave network communication to solve the problems of the incomplete detection of low-orbit targets, unclear detection of high-orbit targets, slow response of the dynamic target, and difficulties in numbering space objects, which can provide a technical guarantee for the space security in China.