Multi-objective evolutionary optimization for geostationary orbit satellite mission planning

In the past few decades, applications of geostationary orbit (GEO) satellites have attracted increasing attention, and with the development of optical technologies, GEO optical satellites have become popular worldwide. This paper proposes a general working pattern for a GEO optical satellite, as well as a target observation mission planning model. After analyzing the requirements of users and satellite control agencies, two objectives are simultaneously considered: maximization of total profit and minimization of satellite attitude maneuver angle. An NSGA-II based multi-objective optimization algorithm is proposed, which contains some heuristic principles in the initialization phase and mutation operator, and is embedded with a traveling salesman problem (TSP) optimization. The validity and performance of the proposed method are verified by extensive numerical simulations that include several types of point target distributions.

Image improvement based on sub-pixel post-integration for a staring imaging system in geostationary orbit

This paper proposes the post-integration technology based on sub-pixel image registration and image fusion to improve the signal-to-noise ratio （SNR） of remote sensing images without motion degradation caused by satellite vibration. A two-dimensional vibration system is set up to simulate satellite disturbance. Image sequences with different exposure times are captured using a high-speed CMOS camera. The displacement plots are compared with the motion data measured by the grating linear encoder. These plots indicate that the accuracy of the registration algorithm is better than 0.1 pixels. The sub-pixel image fusion shows an improvement in image quality, thus indicating that this technology is powerful for staring imaging systems in geostationary orbit.

An investigation on tether-tugging de-orbit of defunct geostationary satellites

In recent years,defunct satellites mitigation in the geostationary orbit(GEO) has become a hot issue in the space field.How to transfer defunct geostationary satellites to the graveyard orbit safely,economically and efficiently presents new challenges to spacecraft dynamics and control.This paper conducts an in-depth investigation on tether-tugging de-orbit issues of defunct geostationary satellites.Firstly,a four-phase tether-tugging de-orbit scheme including acceleration,equilibrium,rotation and return is proposed.This scheme takes into consideration how to avoid the risks of tether ripping,tug-target collision,and tether twist,and how to achieve the mission objective of fuel saving.Secondly,the dynamics model of the tether combination system is established based on Lagrange equation,and the four phases of tether-tugging de-orbit scheme are simulated respectively.Simulation results indicate that the scheme is theoretically feasible and satisfies the design objectives of safety,economy and efficiency,providing a technical approach for engineering application.

Resolution analysis of GEO spaceborne-airborne bistatic SAR based on sliding spotlight mode

For a synthetic aperture radar（SAR） system mounted on a geostationary Earth orbit（GEO） satellite, the track can be curvilinear. Thus, a bistatic SAR system based up on geostationary transmitter and ＂receive-only＂ SAR system onboard airplanes, namely GEO spaceborne-airborne bistatic（GEO SA-Bi SAR）, is significantly different from the traditional bistatic SAR. This paper mainly studies the resolution characteristic of the sliding spotlight GEO SA-Bi SAR system. Firstly, the common azimuth coverage and coherent accumulated time are theoretically analyzed in detail. Then,based on the gradient method, the accurate two dimensional resolution of a GEO SA-Bi SAR system is analytically calculated. Finally, the simulation data show the correctness and effectiveness of the proposed resolution analysis method.

SIMULATION AND ANALYSIS OF PERFORMANCE ON THE COMPASSTM ENHANCED BY GEO AND IGSO

Positioning accuracy of the Global Navigation Satellite System(GNSS) can be analyzed by Positioning Dilution Of Precision(PDOP).In order to enhance the navigating performance of Asia and the Pacific areas,this paper analyzes the next generation BeidouTM navigation satellite system(CompassTM) enhanced by Geostationary Earth Orbit(GEO) and Inclining GeoSynchronized Orbit(IGSO).As global navigation satellite system,CompassTM must be robust enough to avoid system layoff,when some nodes are not available.So,the CompassTM enhanced by GEO and IGSO constellation is proposed and analyzed its PDOP proformance,this paper shows some exciting results of performance of CompassTM enhanced by GEO and IGSO.From the simulation results,we can found that:when more than fifteen satellites are invalid,the enhanced system could be operating normally.

Efficient high-accuracy north-south station-keeping strategy for geostationary satellites

Station-keeping(SK) is indispensable in actual geostationary(GEO) satellite missions. Due to the luni-solar gravity perturbations, the inclination of a GEO satellite suffers the issues of secular drift and long-period oscillation. Current north-south(NS)SK strategies maintain the GEO satellite’s orbit with high accuracy but low fuel efficiency. In this work, an efficient highaccuracy NS-SK strategy is developed for the GEO satellites. First, an averaging method is employed to decrease the accumulation of the secular drift within a one-solar-day SK cycle, while the long-period oscillation caused by the solar gravity is damped to further improve the orbital accuracy using the impulse and finite-thrust propulsions. Second, we contribute a fueloptimal cycle that reduces the fuel consumption and a fixed-interval cycle that executes SK control in fixed time interval every day to further enhance the proposed NS-SK strategy. Numerical simulations show that the improved strategy can achieve highaccuracy NS-SK with little fuel consumption. Moreover, results also demonstrate that the fixed-interval cycle can reach higher NS-SK accuracy while consuming less fuel.

Safe rendezvous scenario design for geostationary satellites with collocation constraints

Rendezvous on the geostationary orbit(GEO)is much more complex than that on the low earth orbit and has a higher critical requirement for safety performance.This paper presents a safe scenario design method for GEO rendezvous proximity missions where the safety constraint of a collocated satellite is considered.A recently proposed quantitative index considering trajectory uncertainty is introduced to analyze the safety performance of the scenario parameters including the V-bar keeping positions and the fly-by trajectory radius.Furthermore,an exhaustive analysis is performed to find the dangerous regions of the V-bar keeping positions and the appropriate semi-major axis of the fly-by ellipse,considering the safety requirements of both the target and the collocated satellite.A geometry method is then developed for designing a feasible and suboptimal safe rendezvous scenario.The method is tested by designing four rendezvous scenarios with±V-bar approach directions respectively in the situations with and without one collocated satellite.Safety performance and velocity increments of the scenarios are compared and a conclusion is reached that the collocated satellite has a significant influence on the scenario design.

Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

The visibility for low earth orbit（LEO） satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system（GPS）. In addition, the spaceborne receivers＇ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination（POD） results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional（3D） accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination（PROD）, the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit（GEO） satellites is illustrated for POD.

Thermal Analysis and Validation of GF-4 Remote Sensing Camera

The Chinese GF-4 satellite remote sensor is the highest spatial resolution among the civil satellite on the geosynchronous orbit, which carries on a camera with spatial resolution of 50 meter in the bands of visible and near infrared red and 400 meter in middle infrared red band. The thermal design of the spacecraft was challenging because the high resolution and the sensitivity requirement to achieve the desired scientific objectives. This paper presents the thermal analysis and test of the GF-4 in GEO orbit. The major findings of the analyses are the following. The GF-4 experiences complex, alternating external heat flux and faces direct sunlight in most of the orbital period. By applying a finite element model, the predicted temperature variation of the components remains in the desired temperature regime even in the extreme conditions. Comparing the thermal analysis results, the difference between the predicted and measured temperatures was less than 3°C for most of the components. The thermal control system functioned properly and the thermal model simulated the actual thermal design of GF-4. This thermal design method realizes the high efficiency and precision thermal control of the first high resolution geostationary orbit camera in China, which can provide reference for the high precision and stability thermal control of large aperture optical camera.