Recover the abnormal positioning, velocity and timing services caused by BDS satellite orbital maneuvers

The BeiDou Navigation Satellite System (BDS) provides global Positioning, Velocity, And Timing (PVT) services that are widely used in various areas. The BDS satellites frequently need the orbit maneuvers due to various perturbations to keep satellites in their designed positions. During these maneuvers, PVT services may be abnormal if the data from a maneuvering satellite is used. In this paper we developed an approach to recover the abnormal PVT services. By using BDS observations from multiple tracking stations, the orbital errors of a maneuvering satellite can be in real time obtained and corrected, thereby avoiding any influence on the performance of PVT services. The tests show that the average precision of position, velocity and timing services are improved by 0.8 m, 0.1 mm/s and 0.16 ns, respectively, using the developed orbital maneuver recovery approach. In addition, the approach can also be used for the orbital maneuver detection and monitoring.

Modelling an Argon Propellant Dual Stage Cylindrical Electrohydrodynamic Thruster at Low Pressure

In recent years, electric propulsion reached a high level of impact for space orbital maneuvers, planetary journeys, or deep space missions mostly because of its significant exhaust velocity, and its high specific impulse. In this study, we model a corona discharge to describe the behaviour of several key parameters in dual-stage electrohydrodynamic (EHD) thrusters investigating two different configurations. It was found that, between the two geometries, the three-electrode geometry was the better method since the four-electrode geometry would create a slowdown area, thus decreasing the output thrust. By setting the first cathode with a negative voltage and the second connected to the ground, the ions and electrons would be accelerated in the first cathode and would be neutralized, by virtue of secondary electron emission taking place in the second. Overall, the dual stage three electrodes EHD thruster spends 8mW of electric power and delivers a thrust of 157nN with an efficiency of 32mN/kW.

Mission Planning for Optical Satellite’s Constant Surveillance to Geostationary Spacecraft

For a mission to constantly watch geostationary (Orbital inclination isn’t 0, GEO) spacecraft by an optical satellite during a whole fly-around cycle, study the relative position relationship between the two and sun during fly-around mission; design the trajectory of the optical satellite, on which, the optical satellite keeps facing to the spacecraft in the direction opposite the Sun. Firstly, for constant surveillance to geosynchronous (Orbital inclination is 0) spacecraft, study from the Keplerian orbit elements, analyze its geometric relationship with the sun and the optical satellite. Then calculate the initial phase interval that meets the requirements of the mission. Compared with Clohessy-Wiltshire equation (CW equation), this method is more concise and the spatial physical meaning is clearer. However, the orbital inclination of GEO spacecraft is usually not 0. Secondly, taking GEO spacecraft with 1° inclination as an example, calculate the initial phase interval of the mission. Thirdly, select an initial phase in the initial phase interval, and design the fly-around trajectory based on CW equation. Lastly, the optical satellite’s position when it receives the mission is initial position, and the position when the fly-around mission starts is final position. The optical satellite’s approach trajectory is summarized as spacecraft's Lambert trajectory optimization. Take the time of two orbital maneuvers as optimization variables, and the fuel consumption as optimization objective. Optimize the plan of orbital maneuvering. The total pulse thrust velocity required for orbital maneuver after optimization in the example is 18.2514m/s, which is highly feasible in engineering. This method can be used for space situational awareness and in-orbit services of GEO spacecraft.

Cloud-Based Experimental Platform for the Space-Ground Integrated Network

The space-ground integrated network (SGIN) is an important direction of future network development and is expected to play an important role in edge computing for the Internet of Things (IoT). Through integration with an SGIN, IoT applications can provide services with long-distance and wide-coverage features. However, SGINs are typical large-scale and time-varying networks for which new network technologies, protocols, and applications must be rigorously evaluated and validated. Therefore, a reliable experimental platform is necessary for SGINs. This paper presents a cloud-based experimental platform for the SGIN context named SGIN-Stack. First, the architecture of SGIN-Stack, which combines the Systems Tool Kit (STK) and OpenStack, is described. Based on this architecture, a seamless linkage between OpenStack and STK is achieved to realize synchronous, dynamic, and real-time network emulation for an SGIN, and the dynamic differential compensation technology and a random number generation algorithm are applied to improve the emulation accuracy for satellite links. Finally, an emulation scenario is constructed that includes six space-based backbone nodes, sixty-six space-based access nodes, and a ground station. Based on this emulation scenario, experiments concerning the satellite link delays, bit error ratio (BER), and throughput are carried out to prove the high fidelity of our SGIN-Stack platform. Emulation experiments involving satellite orbital maneuvers and attitude adjustments show that SGIN-Stack can be used for dynamic and real-time SGIN emulation.

Real-Time Detection of Orbital Maneuvers Using Epoch-Differenced Carrier Phase Observations and Broadcast Ephemeris Data: A Case Study of the BDS Dataset

The orbital maneuvers of the global navigation satellite system (GNSSs) have a significant influence on the performance of the precise positioning, navigation, and timing (PNT) services. Because the Chinese BeiDou Navigation Satellite System (BDS) has three types of satellites in the geostationary orbit (GEO), inclined geosynchronous orbit (IGSO), and medium earth orbit (MEO) maneuvers occur more frequently. Thus, it is essential to determine an effective approach for the detection of orbital maneuvers. This study proposes a method for the detection of orbital maneuvers using epoch-differenced carrier phase observations and broadcast ephemeris data. When using the epoch-differenced velocity estimation as a basic data solution model, the time discrimination and satellite identification factors are defined and used for the real-time detection of the beginning and the pseudorandom noise code (PRN) of satellites. The datasets from four GNSS stations (WUH1, BJF1, POHN, CUT0) from the year 2016 were collected and analyzed. The validations showed that the beginning, the PRN of the orbital maneuver of the satellite can be precisely detected in real time for all GEO, IGSO, and MEO satellites, and the detected results also showed good consistency, with the beginning time at a difference of 1–2 min across different stations. The proposed approach was observed to be more sensitive, and the detected beginning time was about 30 min earlier than the single point positioning approach when the high-precision carrier phase observation was used. Thus, orbital maneuvering can be accurately detected by the proposed method. It not only improves the utilization of the collected data but also improves the performance of PNT services.