Space mapping satellites play an increasingly important role in Space mapping satellites play an increasingly important role in mapping and mapping. The positioning accuracy of mapping satellites is the core and key index for evaluating the performance of Surveying and mapping. At present, it has developed to the precision of the meter level. Therefore, in the design process of Surveying and mapping camera, it is not only necessary to ensure that the image has good MTF, signal to noise ratio, dynamic range and other basic radiation characteristics, but also need to focus on the high precision calibration of the interior orientation elements of optical system distortion, optical axis, focal distance and other questions of orbit stability.<p> </p>In 2012 and 2016, China successfully launched ZY-3 (01/02) satellites, with a three-line-arrays camera and a multispectral camera. It is mainly used for the production of basic geographic information products of 1:50000 scale, and modification and updating of 1:25000 and larger scale topographic maps in China. The satellites have achieved good application results. Based on these experiences, driven by higher precision surveying and mapping requirements, as the main development and research organization of the Chinese space optical remote sensing camera, BISME has carried out a serial of research in the overall design of the space optical surveying camera. This paper gives some own views about the research for discussion and exchange.
According to the interior orientation elements and imaging quality requirements of mapping application to mapping camera and combined with off-axis three-mirror anastigmat(TMA) system, high optomechanical stability design of a space optical mapping camera is introduced in this paper. The configuration is a coaxial TMA system used in off-axis situation. Firstly, the overall optical arrangement is described., and an overview of the optomechanical packaging is provided. Zerodurglass, carbon fiber composite and carbon-fiber reinforced silicon carbon (C/SiC) are widely used in the optomechanical structure, because their low coefficient of thermal expansion (CTE) can reduce the thermal sensitivity of the mirrors and focal plane. Flexible and unloading support are used in reflector and camera supporting structure. Epoxy structural adhesives is used for bonding optics to metal structure is also introduced in this paper. The primary mirror is mounted by means of three-point ball joint flexures system, which is attach to the back of the mirror. Then, In order to predict flexural displacements due to gravity, static finite element analysis (FEA) is performed on the primary mirror. The optical performance peak-to-valley (PV) and root-mean-square (RMS) wavefront errors are detected before and after assemble. Also, the dynamic finite element analysis(FEA) of the whole optical arrangement is carried out as to investigate the performance of optomechanical. Finally, in order to evaluate the stability of the design, the thermal vacuum test and vibration test are carried out and the Modulation Transfer Function (MTF) and elements of interior orientation are presented as the evaluation index. Before and after the thermal vacuum test and vibration test, the MTF, focal distance and position of the principal point of optical system are measured and the result is as expected.
The resolution and observing width of optical remote sensing camera can be enhanced by increasing the detector length of focal plane. Optical butting is used to increase the imaging length owing to its simple structure, low cost and the simultaneously-imaging detectors. But butting process is influenced by many factors, which result in imaging gaps, so overlapping pixels between adjacent detectors is the key. In this paper, the factors causing imaging gap are analyzed, and calculation of overlapping pixel number is given out based on the analysis. Firstly an optical-butting focal plane system is built on optical imaging principles. Then the factors causing imaging gap are listed and analyzed, under the consideration of telecentric and non-telecentric optical system. Based on the imaging gap analysis, a formula for overlapping pixel number calculation is obtained, with the MTF assurance in vignetting districts resulted from optical butting. Finally a calculation example of a camera is given.