Analysis of optical beacon emitter parameters for spacecraft navigation system
Spacecraft (SC) optical observation is one of the main method of SC tracking and measurement of their parameters. The successful development of semiconductor emitters' technology allowed gaining the high-efficient laser diodes with high capacity level at low mass and dimensions parameters. This permits to develop optical beacon systems for spacecraft navigation based on these diodes. Firstly, these are optical beacons installed on planetary landing stations, such as Luna-Glob/Luna-Resource-1 (and in the future - on modules descending to the Martian surface). Installation of such beacons allows high-accuracy location of the landing stations with the help of spacecraft optical TV equipment and ground-based tracking stations. Being connected to the radioisotope power source they can be used as beacons for future lunar missions. The article describes the developed algorithm for semiconductor light sources' selection necessary to solve the problem of optical beacons design for space expeditions: 1. The beacon's radiation should be reliably registered by the receiving optical system. This requires the following steps: - Determination of the necessary emission power. Selection of the emitter's power is stipulated by sensitivity of the receiving ground-based optical system, distance to the spacecraft, the light source radiation angle and, of course, the time of exposure; - Selection of the semiconductor light source allowing creation of low divergent light beams, which is necessary for transmission of this radiation for long distances; - Determination of necessary emission spectrum of the semiconductor light source (rather wide emission spectrum of the semiconductor light source is allowed for “space-to-space” system). In the case of “Spacecraft-Earth” system selection of emission spectrum is stipulated by the atmosphere's properties; - Time persistence of the optical beacon should not exceed the frequency response of the receiving equipment, necessary for signal coding. 2. Optical beacon should provide operation in the space flight conditions: diminutive mass and dimension parameters, long lifetime, radiation and vibration resistance, capability to operate at low voltage, high efficiency. The results of the analysis were used for selection of the optical laser beacon emitters developed within the framework of Luna-Glob and Luna-Resource-1 projects.