The detection of material composition on the surface of celestial bodies has always been an important content in lunar and deep space exploration. At present, the main detection means of material composition on the surface of celestial bodies is visible-near-infrared spectroscopy. Given the wide variety of material components on the surface of celestial bodies, attention should be paid to their chemical properties and content. The current single payload is difficult to meet these requirements, and it is necessary to develop new scientific payload technologies. Over the past two decades, the potential of Raman spectroscopy as a tool for lunar and deep space exploration has been intensively explored. Raman spectroscopy has the advantages of no need to prepare samples, fast and non-destructive analysis, and clear identification of molecular information. Thus, it is very suitable for the insitu detection of celestial bodies. Compared with visible and near-infrared spectroscopy, Raman spectroscopy has unique advantages in the detection of celestial surface materials. 1) The Raman spectrum peaks are clear and sharp without overlapping, which is conducive to the identification of minerals, especially for the composition and content measurement of mixed minerals. 2) It is not only easy to identify feldspar minerals, but also can detect other iron-free minerals. 3) It can detect inorganic substances, hydrous minerals, and organic substances at the same time. Therefore, Raman spectroscopy is a method with important application value and potential for the detection of material composition on the surface of celestial bodies, which complements the advantages of traditional visible light and near-infrared spectroscopy.

Since the first commercial laser Raman spectrometer came out in 1987, Raman spectroscopy, as a powerful spectral analysis technique, has been widely applied in various material analysis fields. In 1995, Wang et al. first proposed the application of Raman spectroscopy on the lunar surface to detect its surface material composition. Subsequently, scientists successively proposed to apply Raman spectroscopy technology to the detection of extraterrestrial celestial bodies such as the moon and Mars and put forward optical probe type short-range detection Raman, long-range Raman, and time-resolved Raman. Raman spectrometers served as a potential payload in the Mars Exploration Rover mission of American and Tianwen-1 mission of China but ultimately were not adopted due to low technology maturity. With the development of lasers, charge-coupled devices, and other instrument components, the application of Raman spectroscopy technology to deep space exploration has become a reality.

After years of verification of principle devices, various countries have added or plan to add Raman spectrometers to the payload queue for deep space exploration. The Perseverance Mars rover launched by NASA in 2020 is equipped with two Raman spectrometers SHERLOC and SuperCam. SHERLOC mounted on the robotic arm is a close-working deep-UV Raman and fluorescence spectrometer. The SuperCam is mounted on the mast and includes an image intensifier-based long-range time-resolved Raman spectrometer with a working distance of 7-12 m. ESA's Mars rover ExoMars is preparing to carry a Raman spectrometer RLS. RLS mounted inside the cabin is a close-range Raman spectrometer with an excitation wavelength of 532 nm. Japan's Phobos mission MMX is also preparing to carry the Raman spectrometer RAX. RAX mounted at the bottom of the rover is a close-range Raman spectrometer with an excitation wavelength of 532 nm. China's Chang'e-7 lunar exploration mission also plans a Raman spectrometer. The Chang'e-7 Raman spectrometer is a long-range time-resolved Raman spectrometer based on an image intensifier, with an excitation wavelength of 532 nm and a working distance of 1.2-3.0 m. Table 1 lists the parameter comparison of the above five Raman spectrometer payloads.

This paper analyzes and discusses the key issues of Raman spectroscopy for deep space exploration. Due to the laser ablation limit of the material, there is a contradiction between the signal intensity of Raman spectroscopy and its spatial resolution. Long-range Raman spectrometers should focus more on signal strength, while close-range Raman spectrometers should focus more on spatial resolution. In terms of excitation wavelength selection, each excitation wavelength has its advantages and disadvantages. The most important thing in the selection of excitation wavelength is to consider the priorities of various scientific mission objectives. Fluorescence suppression is still one of the main problems faced by Raman spectroscopy. Infrared/ultraviolet excitation, time gating, frequency-shift excitation, and photobleaching are effective methods for suppressing fluorescence in deep-space Raman spectrometers. Raman spectroscopy technology for deep space exploration requires the support of many key components, and key components such as intensifiers and gratings still need to be developed.

Raman spectroscopy is a very powerful tool for detecting the composition of astronomical matters and is being applied by increasingly more deep space exploration missions. At present, the development trend of Raman spectroscopy technology for deep space exploration is modularization and miniaturization, multi-technology joint detection, long-range and short-range joint detection, and diversified detection fields.