High precision landing site mapping and rover localization for Chang'e-3 mission

This paper presents the comprehensive results of landing site topographic mapping and rover localization in Chang’e-3 mission.High-precision topographic products of the landing site with extremely high resolutions(up to 0.05 m)were generated from descent images and registered to CE-2 DOM.Local DEM and DOM with 0.02 m resolution were produced routinely at each waypoint along the rover traverse.The lander location was determined to be(19.51256°W,44.11884°N,-2615.451 m)using a method of DOM matching.In order to reduce error accumulation caused by wheel slippage and IMU drift in dead reckoning,cross-site visual localization and DOM matching localization methods were developed to localize the rover at waypoints;the overall traveled distance from the lander is 114.8 m from cross-site visual localization and 111.2 m from DOM matching localization.The latter is of highest accuracy and has been verified using a LRO NAC image where the rover trajeactory is directly identifiable.During CE-3 mission operations,landing site mapping and rover localization products including DEMs and DOMs,traverse maps,vertical traverse profiles were generated timely to support teleoperation tasks such as obstacle avoidance and rover path planning.

Methods of rapid orbit forecasting after maneuvers for geostationary satellites

A geostationary(GEO) satellite may serve as a navigation satellite,but there is a problem that maneuvers frequently occur and the forces are difficult to model.Based on the technique of determining satellite orbits by transfer,a predicted orbit with high accuracy may be achieved by the method of statis-tical orbit determination in case of no maneuver force.The predicted orbit will soon be invalid after the maneuver starts,and it takes a long time to get a valid orbit after the maneuver ends.In order to improve ephemeris usability,the method of rapid orbit forecasting after maneuvers is studied.First,GEO satellite movement is analyzed in case of maneuvers based on the observation from the orbit meas-urement system by transfer.Then when a GEO satellite is in the free status just after maneuvers,the short arc observation is used to forecast the orbit.It is assumed that the common system bias and biases of each station are constant,which can be obtained from orbit determination with long arc observations.In this way,only 6 orbit elements would be solved by the method of statistical orbit determination,and the ephemeris with high accuracy may be soon obtained.Actual orbit forecasting with short arc observation for SINOSAT-1 satellite shows that,with the tracking network available,the precision of the predicted orbit(RMS of O-C) can reach about 5 m with 15 min arc observation,and about 3 m with 30 min arc observation.

APOD mission status and preliminary results

On September 20 th, 2015, twenty satellites were successfully deployed into a near-polar circular orbit at 520 km altitude by the Chinese CZ-6 test rocket, which was launched from the Tai Yuan Satellite Launch Center. Among these satellites, a set of 4 Cube Sats conform the atmospheric density detection and precise orbit determination(APOD) mission, which is projected for atmospheric density estimation from in-situ detection and precise orbit products. The APOD satellites are manufactured by China Spacesat Co. Ltd. and the payload instruments include an atmospheric density detector(ADD), a dual-frequency dualmode global navigation satellite system(GNSS) receiver(GPS and Beidou), a satellite laser ranging(SLR) reflector, and an S/Xband very long baseline interferometry(VLBI) beacon. In this paper, we compare the GNSS precise orbit products with colocated SLR observations, and the 3 D orbit accuracy shows better than 10 cm RMS. These results reveal the great potential of the onboard micro-electro-mechanical system(MEMS) GNSS receiver. After calibrating ADD density estimates with precise orbit products, the accuracy of our density products can reach about 10% with respect to the background density. Density estimates from APOD are of a great importance for scientific studies on upper atmosphere variations and useful for model data assimilation.

Matching suitable feature construction for SAR images based on evolutionary synthesis strategy

In the paper,a set of algorithms to construct synthetic aperture radar（SAR）matching suitable features are frstly proposed based on the evolutionary synthesis strategy.During the process,on the one hand,the indexes of primary matching suitable features（PMSFs）are designed based on the characteristics of image texture,SAR imaging and SAR matching algorithm,which is a process involving expertise;on the other hand,by designing a synthesized operation expression tree based on PMSFs,a much more flexible expression form of synthesized features is built,which greatly expands the construction space.Then,the genetic algorithm-based optimized searching process is employed to search the synthesized matching suitable feature（SMSF）with the highest effciency,largely improving the optimized searching effciency.In addition,the experimental results of the airborne synthetic aperture radar ortho-images of C-band and P-band show that the SMSFs gained via the algorithms can reflect the matching suitability of SAR images accurately and the matching probabilities of selected matching suitable areas of ortho-images could reach 99±0.5%.