主带彗星探测的科学目的及光谱仪设计构想

Scientific Objectives and Design Concepts of Onboard Spectrometers for Main Belt Comets Exploration

由于主带彗星富含水冰等挥发分并且位于火星与木星之间的小行星带区域,因此很可能是给早期地球带来水资源的天体,自从20世纪初期被发现以来引起了行星科学界的极大兴趣,是未来绕飞探测的重要候选目标。总结了主带彗星133P光谱探测的科学目标,并根据不同成分光谱特征分析和热特性研究需求,提出光谱仪的主要指标构想。谱段需覆盖可见至甚长波红外(0.4~50μm),通过可见红外成像光谱仪和热辐射光谱仪两台载荷分别覆盖0.4~5μm和5~50μm的波段范围。可见红外成像光谱仪采用紧凑型光栅分光系统设计,光谱分辨率在可见光谱段优于5 nm,红外谱段优于10 nm,5 km探测距离下空间分辨优于0.5 m,通过低温制冷抑制背景辐射噪声,保证信噪比优于100。热辐射光谱仪采用时间调制型干涉分光方案,由一台双角镜摆臂式干涉仪实现5~50μm的分光,光谱分辨率8 cm-1,5 km探测距离下空间分辨率优于10 m,采用非制冷热释电探测器。通过对两台光谱仪研制过程中涉及的关键技术进行分析,为后续开展工程研制奠定基础。

The discoveries of main belt comets(MBC)in early twentieth century have attracted great interests of the planetary society,as the water ice and other volatile rich MBCs are located in the main belt and thus may have played a fundamental role in supplying water to the early Earth.Therefore,MBCs are very interesting and important candidate objects for the near future space missions.The scientific objectives of optical and infrared spectrometers for a flyby mission are summarized.Then the major technical specifications for the spectrometers are proposed based on the optical and thermal properties of the main belt comet 133P/Elst-Pizarro,one of the major targets.The spectral coverage of the proposed spectrometeris from 0.4 to 50μm,which is realized by two spectrometers covering 0.4~5μm and 5~50μm,respectively.The visible and infrared imaging spectrometer(VIIS)is a very compact grating spectrometer covering 0.4 to 5μm with a spectral resolution of 5 nm in the visible and 10nm in the infrared.The spatial resolution of the VIIS is 0.5 m at an observational distance of 5km.The signal to noise ratio of the spectrometer is better than 100 using cryogenic optics technology.Thermal emission spectrometer(TES)is a time modulated Fourier transform spectrometer.The core component of TES is one interferometer with two cube corners and swing arms which covers 5~50μm.The spectral resolution of TES is 8 cm-1.The spatial resolution of TES is 10 m at an observational distance of 5 km.A pyro-electric detector is used for the TES,working at ambient temperature.The key technologies and specifications for the two instruments are described and analyzed.The current results provide important information for engineering development in the future.