The principle of radio frequency ion thrusters（RIT），as well as the research history and achievements of micro-newton and milli-Newton RIT at home and abroad in the past 60 years，was explained in detail. The radio frequency ion propulsion system involves a number of key technical challenges. Preliminary solutions to the problems of propellant selection， radio frequency（RF）circuit impedance matching，gas flow control，electrical neutralization control and lifetime were proposed， and the development trend and research direction were put forward combined with the future application of RIT.

Soft landing exploration is an important method for exploring extraterrestrial objects, and guidance, navigation and control (GNC) is the key to successful soft landing of extraterrestrial objects. Firstly, the development status of soft-landing missions of foreign and domestic celestial bodies such as Moon, Mars, and small celestial bodies was reviewed. On this basis, the typical GNC schemes for soft landing missions of extraterrestrial objects and the main progress of autonomous navigation and control technology were summarized. Finally, the key technologies for autonomous navigation and control that require special attention and development were proposed for future pinpoint soft-landing missions of extraterrestrial objects, in order to provide the experience and reference for future technological development.

The high precision spacecraft platform system is an important carrier and plays a significant role in the successful implementation of a space gravitational wave detection mission. In this paper, frontier researches on high-precision spacecraft platform systems were reviewed and summarized. The inertial sensor reference of spacecraft platform, micro-thrust actuator, drag-free attitude control technology of spacecraft platform, formation design and control of spacecraft system were discussed. The recent relevant research progress of spacecraft platform system used for space gravitational wave detection was summarized and discussed, covering both domestic and international frontier research hotspots, focusing on key research issues of space gravitational wave detection spacecraft platform system design. A prospect on the development of spacecraft platform system was proposed, including key payloads, orbit and attitude control strategies, formation configuration design, etc

Near-Earth asteroid impact is a major catastrophic threat facing human society. Planetary defense is an inevitable requirement for building a community with a shared future for mankind and continuing human civilization. Implementing on-orbit disposal is the best way to prevent and resolve the risk of near-Earth asteroid impact. This paper systematically combed the development status of near-Earth asteroid defense on-orbit disposal technologies，comprehensively summarized the key technologies，advantages and disadvantages，and application scenarios of nuclear explosion，kinetic impact，gravitational traction，ion beam，laser ablation，tug，mass driver，surface spraying and other on-orbit disposal technologies，and puts forward suggestions for the development of near-Earth asteroid defense on-orbit disposal technology.

A reusable launch vehicle can take off vertically and horizontally, and then land vertically, horizontally, or by parachute, so as to form various combinations of takeoff and landing schemes. Aiming at the different recovery modes of reusable launch vehicle, this paper discusses the key technologies of Vertical Takeoff and Vertical Landing (VTVL), parachute recovery, and Horizontal Takeoff and Horizontal Landing (HTHL), covering key technologies for other combinations. For VTVL mode, three key technologies, such as engine throttling, multiple start-up, and landing mechanism, are analyzed in detail. For parachute recovery, the technologies relating to the landing area control of rocket jettisons and aerial recovery are introduced. For the HTHL mode based on the rocket propulsion system, five challenges including the coupling mechanism under complex aerodynamic thermal environment, thermal protection, landing mechanisms, guidance and control, are discussed. The characteristics of the three recovery modes are briefly summarized and compared.

Small celestial bodies in the Solar system，such as asteroids and comets，have become the key targets in the field of deep space exploration. The exploration of small celestial bodies is of great significance for studying the formation and evolution of the solar system，the origin of life，planetary defense，and the exploitation of space resources. With the continuous development of aerospace technology，the way of small-body exploration has gradually shifted from flyby and orbiting to close-proximity detection methods，such as landing，sampling，and touring. The construction of a high-accuracy gravitational field model in the vicinity of the given small body is crucial to the design and implementation of such close-proximity exploration missions and to the study of dynamics near the small bodies. Thus，this paper first reviews the two-hundred-year history of development of the modeling of gravitational field，and elucidates the basic principles and drawbacks in the different methods. The relationship between the gravitational field near the binary asteroid system and the dynamics of such system is second reviewed. This paper also reviews the techniques for modelling the gravitational interactions in the study of the dynamics of the binary asteroid system. These techniques provide fundamental tools for the binary system mission designs and the study of the formation and evolution of the binaries. Finally，the future research trends are discussed.

The solar wind, solar energetic particles and the galactic cosmic rays can reach the Moon almost unhindered, and interact with the lunar surface. The solar wind is partly scattered by the lunar regolith as hydrogen energetic neutral atoms, and the solar wind can also sputter heavy energetic neutral atoms out of the lunar regolith as well. While the albedo radiation, resulting from impact of the solar energetic particles and the galactic cosmic rays on the lunar regolith, are mainly composed of neutrons and gamma rays, features of the lunar surface radiation environment. The first ever in situ measurements of energetic neutral atoms and particle radiation have been carried out by Chang’E-4 on the lunar farside. Results reveal that a mini-magnetosphere is formed in the vicinity of the Moon, suggesting ENA is a new perspective to study the solar wind - Moon interaction. While the radiation measurements provide valuable information to guarantee the health of future robotic or manned missions to the Moon.

The edge of Solar system is the outermost fence of the heliosphere that protects the homeland of mankind. In recent years，Voyager 1 and Voyager 2 have reached the edge，leaving some major scientific mysteries in a unresolved state because of the limits of the payload function. Therefore，a specific mission for the edge of Solar system contains huge scientific value. Here we introduce the definition of the edge of Solar system and the main detection elements，summarizes the current status of the missions for the outer heliosphere，including the scientific targets and the scientific payload for the missions. Some major scientific issues in heliophysics，interstellar space physics and Solar system evolution，have been presented，as well as the prospects for the scientific goals for our future interstellar mission.

For the aim of scientific exploration of lunar water ice, this review summarizes the challenges and key technologies needed for water ice sampling and detection in the lunar polar region according to the lunar polar environment and the characteristics of lunar water ice. For the demand of selection of water ice sampling site，according to different working principles，five methods were summarized：mechanical sensing，thermoelectric physical property sensing，radar detection，spectrum detection and neutron spectrum detection. Then，for the demand of surface-exposed water ice sampling，three kinds of surface sampling techniques，including scooping，shallow drilling，and grinding were described. For the needs of subsurface buried water ice sampling，first，the subsurface regolith penetration techniques for extraterrestrial objects were summarized，then six kinds of drilling sampling techniques were introduced， including integrated sensing，volatile extraction，lunar surface drilling cuttings acquisition, bit external cuttings acquisition，bit internal cuttings acquisition and coring. Finally，suggestions on technical approaches for China’s implementing lunar water ice sampling and exploration missions were put forward.