Dongxu Li

This paper deals with the guidance problem of close approaching small celestial bodies while autonomously navigating with an optical camera. A combination of a deep reinforcement learning (DRL)-based guidance method and a “Stop-and-Go” (SaG) strategy is here proposed to increase the mission adaptability. Firstly, a robust guidance strategy optimizing fuel consumption and angle-only navigation (AON) observability is trained by DRL. Secondly, the SAG strategy is designed to introduce the mission adaptability and further improve the AON observability. Thirdly, a good match between the SAG strategy and the DRL-based robust guidance is demonstrated. The proposed method was tested in a typical R-bar approaching scenario. Then, the mission adaptability with an onboard application was successfully verified, investigating the policy performance with SAG.

The authors of this paper propose a robust star identification algorithm for a ‘Lost-In-Space’-mode star tracker for lost-cost CubeSat missions. A two-step identification framework and an embedded validation mechanism were designed to accelerate the process. In the first step, a masked distance map is designed to provide a shortlist of stars, and the embedded fast validation process enables the direct output of validated stars before the second step. In the second step, local similarity is utilized to select a set of stars from those shortlisted, and the final validation procedure rejects all unsatisfactory stars. This algorithm can provide reliable and robust recognition even when the captured star images include severe star positioning errors, missing stars and false stars. The proposed algorithm was verified by a simulation study under various conditions. As low-cost star sensors face harsh and unknown environments during deep space CubeSat missions such as asteroid exploration, the proposed algorithm with high robustness will provide an important function.

Conducting a wrinkling analysis for a membrane structure of complex boundary conditions is quite difficult. This paper develops a numerical calculation method for completing a wrinkling analysis of a square membrane structure and a trapezoidal membrane structure with static corner forces. Furthermore, an experimental system for measuring the wrinkle is designed and established to verify the correctness of the method. The difference between simulation analysis results and experimental results is quite small for small corner forces, which means the method used for the wrinkling analysis under small loads is effective.

This paper proposes a modified glideslope guidance method that optimizes a hybrid multiobjective of bearing-only navigation error and fuel consumption. The traditional glideslope guidance fixes uniform maneuver intervals and the initial approach velocity as a predetermined value, making this approach inflexible. In this paper, the maneuver intervals and the initial approach velocity were used as optimization variables, and a hybrid cost function was designed. The tradeoff between the two objectives was analyzed with a bearing-only navigation simulation conducted to reveal the navigation performance following different resulting trajectories. The result showed that the optimal scheduled times of maneuvers remained relatively stable under different tradeoff weights, while a strong correlation between the optimal initial approach velocity and the tradeoff weight was revealed. Therefore, when the optimization has to be solved several times online with different tradeoff weights, the initial approach velocity can be the only optimization variable, leaving the scheduled times of maneuvers fixed in the optimal values achieved offline. These findings provide a potential reference for far-approach trajectory design of bearing-only navigation.

The stretchable composite thin-walled lenticular boom can be used in the unfolding process of a large spacecraft structure, and its buckling characteristic is one of the focuses of structural design. In this paper, firstly, the critical buckling load formula is derived based on Euler’s formula and laminated theory for the axial compression buckling problem of the lenticular boom, and verified by the finite element method. Secondly, the influence law of the lenticular boom section and layer parameters on the critical buckling load is quantitatively analyzed. The results show that the lenticular boom generally undergoes first-order buckling in the outer direction of the symmetrical bonding surface. The critical buckling load is most significantly affected by the radius of the convex arc, followed by the center ordinate of the convex arc, the thickness of the layer, and the angle of the layer. And these parameters are positively related to the critical buckling load. The radius of the concave arc and the length of the straight section have little effect on the critical buckling load. The research methods and conclusions of this paper can provide reference for the engineering design of the lenticular boom structure.

Understanding the dynamic characteristics of solar arrays is important for satellite structural design and attitude control design. Considerable theoretical researches have been carried out towards this problem, but they have not been supported by actual orbit data from outer space yet. In this paper, the on‐orbit vibration characteristic data of solar arrays under the deployment shock are measured by using vibration measurement apparatuses based on structural strain. With these valuable experimental data, more eigenfrequencies of the solar arrays in the microgravity environment are obtained, and the prediction that the vibration of solar arrays will have larger amplitude and longer decay time under vacuum conditions is verified. Moreover, by comparing the eigenfrequency of main vibration under the space condition with that under the ground condition, the accurate value of the system damping ratio is gained, which has an important guideline significant for the structural design of solar arrays.

Dynamic vibration and quasi-static deformation will occur simultaneously for flexible space structures subjected to sudden thermal loads. In this paper, the integrated controller based on modified positive position feedback (PPF) compensator is proposed as an innovative controller for active deformation reduction in flexible space trusses. The controller uses the concept of positive acceleration feedback combined with integral position feedback to provide effective vibration suppression of multiple modes and compensator of quasi-static deformation. To solve the problem of placement optimization for both sensors and actuators, the discrete glowworm swarm optimization (GSO) algorithm based on genic binary coding is suggested. A cantilevered truss is taken as an example for numerically evaluating the performance of the controller for thermally induced deformation control. Numerical results demonstrate that the discrete GSO algorithm is feasible in solving the combinatorial optimization problem. And the proposed controller is significantly effective in controlling both steady-state deformation and transient vibration.

This article concentrates on design and test of a soft suspension system for cantilevered momentum wheel assembly. First, a soft suspension system consisting of four folded beams was designed via the finite element method. Next, a mathematical model was employed to investigate the performance of the soft suspension cantilevered momentum wheel assembly. Finally, the natural frequencies of the cantilevered momentum wheel assembly were verified by ‘hammering test’ and the microvibrations produced were measured by a force-acceleration measurement system consisting of a Kistler table and several accelerometers. The results show that the natural frequencies and critical speed obtained by the experiment coincided well with the mathematical model; the soft suspension system can effectively isolate the disturbances produced by the rotor when the cantilevered momentum wheel assembly operates above the critical speed; and the maximum rotational speed increases from 4900 to 6400 r/min when the vertical beam of the soft suspension system is thickened from 0.0025 to 0.003 m. Thus, the design method is valid to be used for the soft suspension system, and the soft suspension system is particularly efficient for the isolation of vibrations produced by the cantilevered momentum wheel assembly, the disturbance frequencies of which are mainly in the high-frequency range. In addition, the maximum rotational speed of the soft suspension cantilevered momentum wheel assembly can be improved by increasing the stiffness of the suspension system.