The environmental conditions of Mars landing missions are much different from that of Earth reentry missions, including the distance between the spacecraft and the Earth, the atmosphere, landform, aerodynamic forces, thermal effects. Therefore there are more autonomy requirements, more flight phases, more uncertainties in modeling and analysis, and more difficulties in validation of the flight sequence. Firstly the challenges of Mars landing missions are summarized in this paper. Then the key issues for Mars landing missions are analyzed according to the phases of the landing process. Finally suggestions and proposals for further development for Mars landing technologies are given.

Common-track constellation is a special kind of constellation, all ground tracks of satellites are in one track. With recursive orbit or quasi-recursive orbit, the ground track of the constellation is a closed loop with a repeating track. In particular, if the constellation is in one orbit plane, the constellation can meet the requirement for a multi-satellite launch mission and fast satellite-satellite link establishment. The characteristics and coverage properties of a common-track constellation in one orbit plane are studied in this paper. The simulation results show that a common-track constellation in one orbit plane can provide favorable coverage to a target station in the polar areas.

A safety design applies to every stage in a satellite system development life cycle to identify and analyze hazards in the satellite at a system level, eliminating or controlling various safety risks, while verifying the functions of the satellite system have safety characteristics, so as to optimize the satellite system for the best performance in terms of time and cost. This article comprehensively leverages such factors as satellite reliability, complexity and life cycle by considering the overall satellite safety work plan, hazard analysis, hazard sources, pyrotechnic devices and other module safety critical designs. Safety design measures were formulated to review and verify the effectiveness of system functions including a safe power supply to a satellite and pyrotechnic explosives to achieve the safety requirements of the satellite from a development stage. Safety design activities for each subsystem will ensure meeting the development requirements of the satellite system as a whole, and ensure the satellite system cannot be the cause of casualties, equipment damage, property loss, or have a health-threatening impact or detrimental impact on the environment.