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To accomplish high-resolution imaging of the preselected landing area, it was necessary for the Chang'E-2 mission to perform orbital maneuvering on the far side of the moon to meet the conditional height requirement of the imaging area. Engine shutdown would be executed invisibly on the back side of the moon if the descent maneuver mode opposite to the target perilune or the fuel optimal maneuver mode was used. To ensure the satellite safety, the project collectivety required that the engine shutdown should be designed to be executed in the domestic segmental arcs and meet the requirement of satellite emergency treatment simultaneously. Accordingly, the asymmetric-descent orbit control technology was adopted by offsetting the maneuver point, which obtained the orbit control parameters of finite-thrust mode with an iteration algorithm and modified the results with target perilune drift estimation. The Chang'E-2 satellite declined to the target of 100 km×15 km orbit successfully on 26 October 2010, and has been flying for 32 circles in the experimental orbit to accomplish the preselected landing area imaging. This paper describes the mechanism and realization method of the asymmetric-descent orbit control technology and evaluates the maneuver effect with the actual mission data.Chang'E-2 mission, asymmetric-descent orbit control, perilune drift, preselected landing area imaging Citation:Zhou J L, Liu Y, Peng D Y, et al. Chang'E-2 satellite asymmetric-descent orbit control technology.

To guarantee copyright protection and integrity authentication simultaneously, this paper proposed a dual digital watermarking scheme: Transform the image by a two-stage wavelet transform, embed a robust watermark in the low frequency sub image and embed a fragile watermark in the high frequency sub images. A logistic chaos algorithm and a Arnold transform were used to add to the difficulty of breaking, leading to the failure of fragile watermark extraction from tampered image. The algorithm can extract a robust watermark, even though the stego image is badly damaged. It can prove a very feeble modification to the image by a fragile watermark. Theoretical analysis and experimental results show that this technique is an integrated and secure scheme for multimedia production protection.

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