Tianwen-1 (TW-1) is the first Chinese interplanetary mission to have accomplished orbiting, landing, and patrolling in a single exploration of Mars. After safe landing, it is essential to reconstruct the descent trajectory and determine the landing site of the lander. For this purpose, we processed descent images of the TW-1 optical obstacle-avoidance sensor (OOAS) and digital orthophoto map (DOM) of the landing area using our proposed hybrid-matching method, in which the landing process is divided into two parts. In the first, crater matching is used to obtain the geometric transformations between the OOAS images and DOM to calculate the position of the lander. In the second, feature matching is applied to compute the position of the lander. We calculated the landing site of TW-1 to be 109.9259° E, 25.0659° N with a positional accuracy of 1.56 m and reconstructed the landing trajectory with a horizontal root mean squared error of 1.79 m. These results will facilitate the analyses of the obstacle-avoidance system and optimize the control strategy in the follow-up planetary-exploration missions.

The design of complex aerospace systems is a multidisciplinary design optimization (MDO) problem involving the interaction of multiple disciplines. However, because of the necessity of evaluating expensive black-box simulations, the enormous computational cost of solving MDO problems in aerospace systems has also become a problem in practice. To resolve this, metamodel-based design optimization techniques have been applied to MDO. With these methods, system models can be rapidly predicted using approximate metamodels to improve the optimization efficiency. This paper presents an overall survey of metamodel-based MDO for aerospace systems. From the perspective of aerospace system design, this paper introduces the fundamental methodology and technology of metamodel-based MDO, including aerospace system MDO problem formulation, metamodeling techniques, state-of-the-art metamodel-based multidisciplinary optimization strategies, and expensive black-box constraint-handling mechanisms. Moreover, various aerospace system examples are presented to illustrate the application of metamodel-based MDOs to practical engineering. The conclusions derived from this work are summarized in the final section of the paper. The survey results are expected to serve as guide and reference for designers involved in metamodel-based MDO in the field of aerospace engineering.

A growing interest in small body exploration has motivated research into the rapid characterization of near-Earth objects to meet economic or scientific objectives. Specifically, knowledge of the internal density structure can aid with target selection and enables an understanding of prehistoric planetary formation to be developed. To this end, multi-layer extensions to the polyhedral gravity model are suggested, and an inversion technique is implemented to present their effectiveness. On-orbit gravity gradiometry is simulated and employed in stochastic and deterministic algorithms, with results that imply robustness in both cases.

An increasing number of objects are being launched into low-Earth orbit. Consequently, to avoid the possibility of future in-orbit collisions space object removal techniques are receiving attention. As one of the most developed techniques, drag augmentation is increasingly being considered as an option for end-of-mission removal of objects from low-Earth orbit. This paper highlights a common misconception around drag augmentation: although it can be used to reduce de-orbit time, when used inappropriately it can increase the volume swept by an object and, thus, increase the occurrence risk of collision with another space object. Knowingly ignoring this increased risk of collisions could leave spacecraft operators, and consequently their responsible state party, open to liability risk. By investigating the volume swept and de-orbit lifetime, a strategy of delayed deployment is proposed as a compromise between reducing volume swept and time to de-orbit. However, this increases system complexity and, likely, cost.

From March 20, 2019 to April 30, 2019, the 10th China Trajectory Optimization Competition (CTOC10) was jointly held by the Chinese Society of Theoretical and Applied Mechanics and Nanjing University of Aeronautics and Astronautics. The CTOC10 focused on trajectory optimization for Jovian exploration. The team from Harbin Institute of Technology won the first prize. In this paper, first, the history of the CTOC is presented. Subsequently, the mission of the CTOC10 is introduced, and an account of the final rankings of the competition is given. Finally, trajectory optimization methods are discussed, and suggestions for practical missions are provided.

Resident space object population in highly elliptical high perigee altitude (> 600 km) orbits is significantly affected by luni-solar gravity. Using regularization, an analytical orbit theory with luni-solar gravity effects as third-body perturbations in terms of Kustaanheimo-Stiefel regular elements is developed. Numerical tests with different cases resulted in good accuracy for both short- and long-term orbit propagations. It is observed that the luni-solar perturbations affect the accuracy of the analytical solution seasonally. The analytical theory is tested with the observed orbital parameters of the few objects in highly elliptical orbits. The analytical evolution of osculating perigee altitude is found to be concurrent with observed data. Solar perturbation, when compared with lunar perturbation, is established to be dominant over such orbits.

In an asteroid sample-return mission, accurate position estimation of the spacecraft relative to the asteroid is essential for landing at the target point. During the missions of Hayabusa and Hayabusa2, the main part of the visual position estimation procedure was performed by human operators on the Earth based on a sequence of asteroid images acquired and sent by the spacecraft. Although this approach is still adopted in critical space missions, there is an increasing demand for automated visual position estimation, so that the time and cost of human intervention may be reduced. In this paper, we propose a method for estimating the relative position of the spacecraft and asteroid during the descent phase for touchdown from an image sequence using state-of-the-art techniques of image processing, feature extraction, and structure from motion. We apply this method to real Ryugu images that were taken by Hayabusa2 from altitudes of 20 km-500 m. It is demonstrated that the method has practical relevance for altitudes within the range of 5-1 km. This result indicates that our method could improve the efficiency of the ground operation in the global mapping and navigation during the touchdown sequence, whereas full automation and autonomous on-board estimation are beyond the scope of this study. Furthermore, we discuss the challenges of developing a completely automatic position estimation framework.