Orbit Design Elements of Chang’e 5 Mission

The three key orbit design technologies employed in the Chang’e 5 mission are identified and discussed in this paper: orbit design for lunar orbit rendezvous and docking, orbit design for precision lunar landing and inclination optimization, and orbit design for Moon-to-Earth transfer. First, an overview of the Chang’e 5 mission profile is presented, which is followed by detailed discussions of the three key orbit design technologies, including an introduction of the tracking-based orbit design methodology. Flight data are provided to demonstrate the correctness of the designs.

Mathematical Modeling Methods in Designing Onboard Laser-Ranging Systems of Spacecraft

To perform rendezvous and docking of spacecraft (SC), it is necessary to detect and measure the coordinates of a passive space vehicle (SV) using the onboard aids of an active SV. For this purpose, in addition to radio engineering systems, laser-ranging systems (LRS) are used. A designing process of the onboard LRS for promising spacecraft is currently becoming more complicated and requires taking into account a lot of factors.The authors have developed the PC software to assess capabilities of onboard pulse LRS of spacecraft when working on the nearby or distant space objects that have a diffusely scattering surface, as well as are equipped with the corner reflectors. The software also allows us to calculate the LRS parameters, which, according to GOST R 50723-94, ensure eye-safety in the spectral range of 0.81 ... 1.5 microns in case of accidental irradiation.The energy of the intensifier pulse and the divergence of a sensing beam determine the LRS range and the distance of eye-safe observation, which are the most important indicators to characterize the onboard LRS capabilities. To ensure the best LRS range and safety characteristics simultaneously, it is necessary to solve the problem of multi-criteria optimization.The paper solves the problem of multi-criteria optimization for the maximum LRS range and the eye-safe observation distance by Pareto sets the use of which allows us to avoid uncertainty in choosing a significance of criteria.The results obtained show that the proposed methods can be successfully applied in designing onboard LRS of spacecraft.

Adaptive Finite-Time Control on SE(3) for Spacecraft Final Proximity Maneuvers with Input Quantization

In this paper, a bounded finite-time control strategy is developed for the final proximity maneuver of spacecraft rendezvous and docking exposed to external disturbance and input quantization. To realize the integrated control for spacecraft final proximity operation, the coupling kinematics and dynamics of attitude and position are modeled by feat of Lie group SE 3 . With a view to improving the convergence rate and reducing the chattering, an adaptive finite-time controller is proposed for the error tracking system with one-step theoretical proof of stability. Meanwhile, the hysteresis logarithmic quantizer is implemented to effectively reduce the frequency of data transmission and the quantization errors are reduced under the proposed controller. The algorithms outlined above are based on an integrated model expressed by SE 3 and denoted by uniform motion states, which can simplify the design progress and improve control precision. Finally, simulations are provided to exhibit the effectiveness and advantages of the designed strategy.

Stochastic model predictive control for spacecraft rendezvous and docking via a distributionally robust optimization approach

A stochastic model predictive control (SMPC) algorithm is developed to solve the problem of three-dimensional spacecraft rendezvous and docking with unbounded disturbance. In particular, we only assume that the mean and variance information of the disturbance is available. In other words, the probability density function of the disturbance distribution is not fully known. Obstacle avoidance is considered during the rendezvous phase. Line-of-sight cone, attitude control bandwidth, and thrust direction constraints are considered during the docking phase. A distributionally robust optimization based algorithm is then proposed by reformulating the SMPC problem into a convex optimization problem. Numerical examples show that the proposed method improves the existing model predictive control based strategy and the robust model predictive control based strategy in the presence of disturbance. doi:10.1017/S1446181121000031

A mathematical model for evaluating adhesion contact of an elastomeric seal-on-seal structure

For low impact docking systems (LIDS) developing for rendezvous and docking of spacecraft, the main interface docking seal (MID seal) is one of the key components, and its seal and adhesion performances are crucial for mating LIDS-adapted spacecrafts. An elastomeric seal-on-seal structure is one of the mainstream designs of the MID seal and is generally made of silicone rubbers that can adapt to complex space environments. For the MID seal of seal-on-seal structure, the adhesion performance has been confirmed to have significant effects on the separation reliability of mating spacecrafts. By analyzing the sealing and adhesive mechanisms of the MID seal that is an elastomeric seal-on-seal structure, an adhesive contact model of single rough peak is derived on the grounds of Johnson, Kendall and Roberts (JKR) theory. Utilizing the asperities model and the adhesive contact model of single rough peak, an adhesive contact model of the elastomeric seal-on-seal structure is further proposed. The experiments were performed to verify the adhesion model, and the satisfied consistencies were presented in the comparative studies of the experimental data and the calculated data. Based on the proposed mathematical model, the simulation analyses were performed to disclosure adhesive performances of the MID seal. The influence rules of some parameters on adhesive performances were presented, including material parameters, geometric parameters, and parameters of surface morphology. The research findings are proven to be favorable for the design, machining, assemblage and actual service of the MID seal, and can be also used for other elastomeric seals.