Energy-saving control of geostationary satellite during long-term mothballing

The Chinese Area Positioning System (CAPS) is a new type of satellite navigation systems. The geostationary satellites for normal communication with 2 or 3 sets of inclined geostationary orbit (GEO) satellites are employed to construct a satellite navigation system. The navigation signals are constructed and disseminated on the ground, and the satellites only transfer the signals to the ground by transponders. Such a system is easy to construct. But for such a positioning system, it needs precise and accurate orbit determination of geostationary satellites. A GEO satellite is placed at an altitude of 36000km above the equator and its movement with respect to the station on the ground is very small, so it is very difficult to determine the orbit precisely. An original method for determination of satellite orbits based on pairs of combined observations is developed at the National Time Service Center, Chinese Academy of Sciences. A special ranging observation with the distance between two stations via a satellite, called pairs of combined observations, is proposed. The satellite behaves with such an observation is not a ball, but an ellipse ball. The Dilution of Precision (DOP) is much less than those methods such as the SLR observation. The advantage of pairs of combined observations is that clock offsets for all observing stations and on-bound are cancelled by the method itself, so, the accuracy and precision of orbit determination is not affected by the clock offsets and the DOP is greatly improved. The ranging signals are generated and measured on the ground, and the instrumentation errors can be determined in real time with a high accuracy. Therefore, such a system is very stable. A very high rate of the PN code is employed, a disseminated power is very low, and it can observe signals from remote stations with a lower power less than 1w. With the spread-spectrum technique, multi-stations can work at the same time and same carrier frequency. It can reach the accuracy of raging about 1 cm. The accuracy and precision of the orbit determination are very high, up to a few centimeters. The observing system with the model proposed above for the GEO satellites including 5 stations (one main station and 4 slave stations) placed in China has been set up. The combined observations were made between the main station and the slave stations. The number of combined observations for the 5 stations is 9. The observations are made per second. The observations for 8 sets of satellites are continuous, lasting for about 5 years. The results for the GEO observations show that the observation residuals of the satellite orbit determination for a 3-day solution are 4.0 cm. With the development of the method to determine the orbit based on the discussion above, it is very easy to correct the orbit with observations nearly in real time. Obviously, the method proposed by the National Time Service Center is suitable for precise orbit determination of GEO satellites in a satellite navigation system, and also it is suitable for satellite management and deep space tracking.

The Wide Area Augmentation System(WAAS) is the most mature satellite-based augmentation system currently available to provide higher performance navigation and positioning services for civil aviation users. WAAS broadcasts a wide range of differential correction data and integrity information to users via Geostationary Orbit(GEO) satellites to achieve enhanced navigation performance of GNSS. This paper selects the enhanced messages broadcast by different GEO satellites from February 1st to February 7th, 2022, decodes and compares the data of the messages MT2-5 and MT25, and analyzes the differences of the messages broadcast by different GEOs.

This paper addresses the problem of orbital pursuit-evasion game for geostationary orbit (GEO) satellites using the Deep Deterministic Policy Gradient (DDPG) algorithm to control impulsive orbital maneuvers, with both sides trained simultaneously. Firstly, the kinematics of GEO satellite orbital motion is modeled, and the Runge-Kutta method is employed for orbital propagation to provide an interactive environment for reinforcement learning. Secondly, a game-based training framework is established based on the DDPG algorithm. Finally, the state space and action space within the framework are designed, and a novel PD-DDPG algorithm is proposed to control the pursuit-evasion process. The results demonstrate that the proposed algorithm effectively guides the agents to complete the task and accelerates the convergence rate.

One of the main challenges in the co-existence of geostationary satellite orbit (GSO) and non-geostationary satellite orbit (NGSO) satellite networks is to mitigate the in-line interference caused by an NGSO satellite to the GSO earth terminal, while the NGSO satellite is crossing the GSO satellite’s illumination zone. The method recommended in ITU-R S.1325-3 involves utilizing a range-based power control on the NGSO satellite for downlink communication to the NGSO earth terminals. In this paper, we investigate a cognitive range-based power control algorithm while taking into account the imposed interference level to the GSO fixed satellite service (FSS) system. Results show that the proposed cognitive power control algorithm can mitigate the harmful in-line interference on the GSO terminal receiver, while also providing the desired link quality for the NGSO system. More importantly, we formulate and solve an optimization problem with the objective of minimizing the inter-site distance (ISD) of the GSO-NGSO earth user-terminals. Finally, we develop an analytical method to calculate the ISD between GSO and NGSO earth terminals and validate this with the help of simulation results.

Aiming at the problem of computing offloading with resource constraints in edge computing of dual-layer satellite networks, each low earth orbit (LEO) satellite can offload computing workloads to Geostationary Orbit (GEO) satellites. In order to obtain the optimal strategy for radio resource allocation and offloading decision-making, the system overhead minimization problem is studied, and the offloading decision problem is modeled as a two-sided matching game problem with LEO satellites and GEO satellites as participants. The solution of the offloading decision is given by an improved two-sided many-to-one matching game algorithm with a preference for delay and energy cost. Simulation results show that by effectively offloading decision-making and power, bandwidth, and computing resource allocation, the proposed algorithm can achieve remarkable performance in satellite network edge computing. Meanwhile, compared with the existing methods, the proposed offloading algorithm can effectively reduce the running time of the offloading decision algorithm by 55.53% while the system overhead is reduced by 8.8%.

A proposed mission plan for the TOPAZ powered spacecraft would have the spacecraft start at a 28.5° inclined circular orbit and spiral outward until well above the geostationary equatorial orbit (GEO). With communication and weather satellites located approximately every 2° at GEO, there is a probability that the TOPAZ powered spacecraft will pass near one of these satellites. A simple calculation shows that the low power of the TOPAZ spacecraft (125 kWt) combined with its high relative velocity (1,514 m/s) results in a very small dose to a satellite in equatorial orbit. There is a probability of 10−6 that the TOPAZ will pass within 200 m of a satellite; at 200 m the resulting gamma dose will be less than 1 mr and the integrated neutron flux will be on the order of 1010 n/m2. Other scenarios are equally benign.

Line-of-sight communications links between satellites allow data to be transmitted directly from one satellite to another. The different types of links which can be implemented between satellites in geostationary orbit (GSO) and low Earth orbit (LEO), are illustrated. There are two main classes, interorbit links between LEO and GSO satellites, and intersatellite links (ISLs) between satellites which are both in GSO or LEO orbit. This paper is primarily concerned with ISLs between GSO satellites for military communications.

As space-rated technologies become more compact, more available, and less expensive over time, the concept of accomplishing traditionally large and expensive spacecraft missions using smaller nanosatellite-class spacecraft becomes increasingly feasible. This research focuses specifically on a CubeSat mission to assist with radio frequency (RF) domain verification; that of characterizing and mapping spot beams from communications satellites in geostationary orbit. By flying a CubeSat (or a constellation of CubeSats) through the edges of spot beams originating from geostationary communication satellites, the spot beam’s coverage area will be characterized. This research conducts a mission feasibility assessment, identifies the mission requirements to complete a spot beam mapping CubeSat mission, and examines various constellation configurations that could complete the spot beam mapping mission effectively. It was found that certain CubeSat constellations performed better than others, specifically regarding mapping time, responsiveness to changing conditions, spot beam detection capability, and overall mapping resolution. Constellations with CubeSat formations that utilized a specific spacing angle between themselves in an orbital plane could be tailored to produce spot beam maps with the best resolution; however constellations with a single plane of evenly-spaced CubeSats tended to produce better results over shorter durations. Separating CubeSats into separate planes tended to increase responsiveness and overall map resolution, but doing so required more time to form a comparable solution.

SummaryIn this paper, we study two dynamic frequency hopping (DFH)–based interference mitigation approaches for satellite communications. These techniques exploit the sensing capabilities of a cognitive radio to predict future interference on the upcoming frequency hops. We consider a topology where multiple low Earth orbit satellites transmit packets to a common geostationary equatorial orbit satellite. The FH sequence of each low Earth orbit–geostationary equatorial orbit link is adjusted according to the outcome of out‐of‐band proactive sensing scheme, performed by a cognitive radio module in the geostationary equatorial orbit satellite. On the basis of sensing results, new frequency assignments are made for the upcoming slots, taking into account the transmit powers, achievable rates, and overhead of modifying the FH sequences. In addition, we ensure that all satellite links are assigned channels such that their minimum signal‐to‐interference‐plus‐noise ratio requirements are met, if such an assignment is possible. We formulate two multi‐objective optimization problems: DFH‐Power and DFH‐Rate. Discrete‐time Markov chain analysis is used to predict future channel conditions, where the number of states are inferred using k‐means clustering, and the state transition probabilities are computed using maximum likelihood estimation. Finally, simulation results are presented to evaluate the effects of different system parameters on the performance of the proposed designs.

Satellite communications, in telecommunications, the use of satellite can provide communications links between various points on the earth. Typical satellite communication is composed of a communication satellite, a signal transmitter and a signal receiver. As the signal transmitter or the signal receiver, an earth station plays a vital role in the satellite communications. Accurately adjustment of antenna azimuth, elevation and polarization angles on the earth station is the key to satellite communications. In the present paper, a study of polarization tracking of earth station is presented, and a detailed adjustment procession of the polarization angle is given. Combing with observation series of MEASAT-2 satellite in geostationary orbit, the polarization tracking accuracy is verified. The method can be embeded into computer program of antenna polarization adjustment in earth station.

Based on the principle of TWSTFT, the technology of satellite Orbit Determination by Two-way Tracking (ODTT) is proposed in this contribution. In contrast to the TWSTFT, the signal is transmitted from and received by the same station in ODTT. The time delay of the signal from the station to the Geostationary (GEO) satellite, and then back to the station can be precisely measured, which realizes the range determination between the station and the satellite. Based on the determined ranges of several stations and dynamic models for orbit determination, precise satellite orbits can be obtained. In this study, in addition to the ODTT measurement model, the methods of correcting the station hardware delays, the tropospheric and the ionospheric delays are explained in details. In collaboration with several other institutions, National Time Service Center (NTSC), Chinese Academy of Sciences(CAS) setup a Two-way Tracking network of 5 stations in China, and performed a large amount of experiments for GEO satellite orbit determination. The results show that the precision of the range measurements is about 2 cm, and the GEO satellite orbit precision is a few meters with long arc observation. According to the experimental results, the main characters of ODTT are shown as follows: 1) the ranges measured by the ODTT do not include the time difference between the ground and the satellite clocks, which is beneficial for realizing the precise orbit determination; 2) the measurement precision is very high, i.e., about 2 cm; 3) the ODTT utilizes the microwave frequency and the technology of spread spectrum, which supports the orbit determination for satellites of high orbits and the measurements in diverse atmosphere conditions. The ODTT is a new space technology under development. It will support the research of spatial sciences and geosciences in the future.

In little more than two decades, communications satellite technology has gone from being revolutionary to commonplace, from an idea to world wide service. In both industrialized and developing countries, economic and social progress depends on improved telecommunications. Like other means of transport, telephones, computers, satellites and fiber optic cables and their proper interfaces are essential for moving commercial goods and services. Benefits of satellite communications should in the 1990's be extended to users in all parts of the world through the use of smaller, inexpensive and less sophisticated Earth stations for two way (voice and data), and one way (video, data) use. While earlier satellite systems have been designed and implemented using C and S band communications with satellites in geostationary orbits (GEO), K band communications using VSATs (Very Small Aperture Terminals) have enabled the communications across areas of the US and the world where extensive telecommunications networks did not exist and/or were not affordable. In addition, several systems have been proposed (being built) to provide for the global communication of the mobile users using clusters of smaller, less complex satellites in low Earth orbit (LEG) and medium Earth orbit (MEO). Mobile satellite systems are the future of the satellite communications technology applications. In this presentation, we will briefly summarize the status for satellite communications and then present a comparison of the enabling mobile satellite communications technologies and mobile satellite systems currently being developed. We will also review applications of these systems in public and commercial areas in this presentation. >

This paper reports results from an investigation into possible total electron content (TEC) on ray paths between GPS satellites and satellites in geostationary orbit. The Sheffield University Plasmasphere Ionosphere Model (SUPIM) has been used to estimate the TEC for conditions appropriate to solar maximum as a first step to assessing possible errors in the potential use of the navigation satellites for station keeping in the geostationary orbit. It has been found that in general, for paths through the plasmasphere, where the satellite‐to‐satellite geometry is far removed from eclipse by the Earth's horizon, the TEC is usually less than 20 TECU (total electron content units, 1 TECU = 1016 el m−2) with resultant errors in single‐frequency GPS positioning of a only a few meters. However, when the rays cross the equatorial F2 ionosphere at near‐grazing incidence close to the layer peak, TEC of up to some 2000 TECU have been found, with consequent potential single‐frequency GPS positioning uncertainties of hundreds of meters. The exact magnitudes of the TEC are very dependent on the precise geometry and vary significantly with time, so they would be difficult to simulate in any real‐time, model‐based mitigation system.

The code-phase divergences, which are minimal for GPS, GLONASS, and Galileo satellites, are commonly found in BeiDou Navigation Satellite System (BDS) Geostationary Orbit (GEO), Inclined GeoSynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites. Several precise positioning applications which use code observations are severely affected by these code biases. We present an analysis of code bias based on multipath (MP) combination observations. To mitigate the effect of BDS code bias on precise positioning, we proposed a periodical correction method using a low-pass filter for BDS GEO, IGSO and MEO satellites. The auto-correlation of MP series over long periods is analyzed to obtain the periods of the dominant repeating components for three types of BDS satellites. The periods of the dominant daily repeating components are close to 86,160 s for BDS GEO and IGSO satellites while 603,120 s for MEO satellites. The zero phase-shift low-pass filter was used to extract the low-frequency components of MP series and then low-frequency components are applied to mitigate the code bias periodically. The developed correction methods can make a more remarkable improvement for the accuracy of MP series, compared to the current elevation-dependent correction models. Data sets collected at 50 Global Navigation Satellite System (GNSS) ground stations including 15 of the International GNSS Monitoring and Assessment System (iGMAS) and 35 of the Multi-GNSS Experiment (MGEX) stations are employed for this study. To analyze the influence of code bias on precise positioning and validate the effectiveness of the correction methods, some applications such as single point positioning (SPP), wide-lane (WL) ambiguity analysis and Uncalibrated Phase Delays (UPDs) estimation are conducted. After applying the proposal correction method to the code observations, SPP solutions outperform the uncorrected ones in term of positioning accuracy. The positioning accuracy decreased by 0.28 and 0.1 m in the north and east components and the improvements are more significant for the U components decreased by 0.42 m. In addition, the systematic variations of Melbourne-Wübbena (MW) combination are greatly removed and the convergence time of the MW series are decreased. Moreover, significant improvement is also achieved in terms of the usage rate and residuals of UPDs estimation.

Although Ka-band links to communication satellites in geostationary orbit (GEO) have been used for many years, their use in communicating with communication and remote sensing satellites in low earth orbit (LEO) is still emerging. Of particular interest to designers is characterization of the rate of fading, i.e., the so-called fade slope, which is accentuated on links to satellites to LEO by the rapid manner in which the Earth-space path sweeps though rain cells in the vicinity of the Earth station as the satellite passes across the sky. Fade slopes steepen as the orbital altitude of the satellite decreases and as the intensity of individual rain cells increases. The result has important implications for the design of the power control loops and other mitigation strategies used to mitigate rain fading on such links. Only a few satellites in LEO carry Ka-band propagation beacons or receivers suitable for use in propagation studies and, for various reasons, relatively little measurement data to support design of such links is available.