SAR regional all-azimuth observation orbit design for target 3D reconstruction

Three-dimensional(3D) synthetic aperture radar(SAR)extends the conventional 2D images into 3D features by several acquisitions in different aspects. Compared with 3D techniques via multiple observations in elevation, e.g. SAR interferometry(InSAR) and SAR tomography(TomoSAR), holographic SAR can retrieve 3D structure by observations in azimuth. This paper focuses on designing a novel type of orbit to achieve SAR regional all-azimuth observation(AAO) for embedded targets detection and holographic 3D reconstruction. The ground tracks of the AAO orbit separate the earth surface into grids. Target in these grids can be accessed with an azimuth angle span of360°, which is similar to the flight path of airborne circular SAR(CSAR). Inspired from the successive coverage orbits of optical sensors, several optimizations are made in the proposed method to ensure favorable grazing angles, the performance of 3D reconstruction, and long-term supervision for SAR sensors. Simulation experiments show the regional AAO can be completed within five hours. In addition, a second AAO of the same area can be duplicated in two days. Finally, an airborne SAR data process result is presented to illustrate the significance of AAO in 3D reconstruction.

Overview of China’s 2020 Mars mission design and navigation

Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet.For China’s 2020 Mars exploration mission to achieve success,many key technologies must be realized.In this paper,China’s 2020 Mars mission and the spacecraft architecture are first introduced.Then,the preliminary launch opportunity,Earth–Mars transfer,Mars capture,and mission orbits are described.Finally,the main navigation schemes are summarized.

Orbit design and mission planning for global observation of Jupiter

This paper presents the method created by the National University of Defense Technology(NUDT)team in the 10th China Trajectory Optimization Competition,which entails a 3-year observation mission of 180 regions on Jupiter.The proposed method can be divided into three steps.First,a preliminary analysis and evaluation via an analytical method is undertaken to decide whether the third subtask of the mission,i.e.,exploring the Galilean moons,should be ignored.Second,a near-optimal orbit for magnetic field observation is designed by solving an analytical equation.Third,a set of observation windows and their sequence are optimized using a customized genetic algorithm.The final index obtained is 354.505,ranking second out of all teams partaking in the competition.

Stable periodic orbits for spacecraft around minor celestial bodies

We are interested in stable periodic orbits for spacecraft in the gravitational eld of minor celestial bodies.The stable periodic orbits around minor celestial bodies are useful not only for the mission design of the deep space exploration,but also for studying the long-time stability of small satellites in the large-size-ratio binary asteroids.The irregular shapes and gravitational elds of the minor celestial bodies are modeled by the polyhedral model.Using the topological classi cations of periodic orbits and the grid search method,the stable periodic orbits can be calculated and the topological cases can be determined.Furthermore,we nd ve di erent types of stable periodic orbits around minor celestial bodies:(1)stable periodic orbits generated from the stable equilibrium points outside the minor celestial body;(2)stable periodic orbits continued from the unstable periodic orbits around the unstable equilibrium points;(3)retrograde and nearly circular periodic orbits with zero-inclination around minor celestial bodies;(4)resonance periodic orbits;(5)near-surface inclined periodic orbits.We take asteroids 243 Ida,433 Eros,6489 Golevka,101955 Bennu,and the comet 1P/Halley for examples.