Location. The meaning of specific parameters is shown in figure 1. After defining the meaning of the six orbital parameters, we need to study the mathematical relationship between the parameters and find out how they determine the satellite orbit. For the orbit of an artificial earth satellite, it is a vector from the center of the earth to perigee. The modulus of this vector is what we call orbital eccentricity. Orbit eccentricity e is the ratio of semi-focal length c to semi-major axis a, which is a dimensionless number. The semi-major axis a of the track indicates the size of the track. In practical application, the average motion is usually used instead of A as the classical orbital element. Perigee time τ is an important parameter to determine the on-orbit position (true perigee angle V) of artificial earth satellite at a certain moment. They can be related by Kepler equation and Gaussian equation. When a is determined, M0 at a certain time t0 can be used instead of τ as the orbital elements. In addition, due to the existence of perturbation factors such as the aspheric surface of the earth, the satellite does not actually move in a closed elliptical orbit. In order to study the orbit of artificial earth satellite by using the classical planetary elliptical orbit theory, the motion of artificial earth satellite is often regarded as elliptical motion in space dynamics. Every point in the actual orbit of the satellite is regarded as a point on the ellipse, but the size, shape, perigee direction and the position and direction of the elliptical plane in space are different. This elliptical orbit at a certain point in the actual orbit is usually called a compact orbit. The speed of the satellite at this point is equal to the speed of the satellite at this point in close orbit; This point is called the tangent point of the actual orbit and the near orbit at a given moment. The classical orbit parameters of satellites we are talking about actually refer to the classical orbit parameters of near-earth orbit at a given moment, which are called epochs (a certain point on the time scale). At present, the practical satellite orbit determination means and its theoretical basis The process of calculating the number of a group of orbits at a certain time (called epoch) by using the external ballistic measurement data or autonomous navigation data of artificial earth satellites is called artificial earth satellite orbit determination. Strictly speaking, the whole orbit determination process should include several links, such as pretreatment of measurement data, initial orbit determination and improvement of orbit difference. After investigation, the practical means of satellite orbit determination are mainly divided into two categories: optical measurement and radio measurement. Among them, optical measurement mainly uses optical instruments such as telescope, optical theodolite, high-speed camera and laser rangefinder to track and measure satellites. The main theoretical basis of optical measurement is pure angle observation and orbit determination, which does not need the cooperation of too many satellites, but only needs to observe and record its motion. The orbit of a satellite can be determined on the premise that there are at least three observation data at different times. However, because it is an optical method, its tracking range is limited due to the influence and limitation of satellite size, surface reflection characteristics, observation time, weather and other factors, and it cannot guarantee to determine the orbit at any time. In addition, this method requires very sophisticated optical observation instruments to determine the orbit of the geostationary satellite, which further increases its limitations. Radio measurement is to transmit signals to the satellite through the ground monitoring station and receive the downlink signals of the satellite, so as to calculate the motion parameters of the satellite and determine the orbit of the satellite through the motion parameters. The advantage of radio measurement is that it is not affected by the weather and can realize all-weather tracking measurement. Commonly used satellite radio orbit measurement systems are mainly divided into monopulse radar orbit measurement system, Doppler velocity measurement system and interferometer system. Monopulse radar is a kind of accurate tracking radar. Each time a pulse is transmitted, the antenna can form several beams at the same time, and the amplitude and phase of the echo signal of each beam are compared. When the target is located on the antenna axis, the amplitude and phase of the echo signals of each beam are equal, and the signal difference is zero. When the target is not on the antenna axis, the amplitude and phase of the echo signals of each beam are not equal, resulting in signal difference. Drive the antenna to the target until the antenna axis is aligned with the target, so that the high and low angle and azimuth of the target can be measured, and the distance of the target can be measured from the sum of the signals received by each beam, thus realizing the measurement and tracking of the target. Monopulse radar usually includes amplitude comparison monopulse radar and phase comparison monopulse radar. This orbit measurement method has high angular accuracy, resolution and data rate, but the equipment is complex and the mobility is poor, so it is mainly used for the measurement of low-orbit satellites. Doppler velocimetry system is usually divided into single-station Doppler system and multi-station Doppler system. This orbit determination method mainly relies on Doppler effect. The so-called Doppler effect means that when the objects emitting fixed frequency waves move relative to the observation site, the frequency received by the observation site is not the original fixed frequency, but changes with their relative speed. Its changing law is that when the object is close to the observation point, the wavelength becomes shorter and the frequency becomes higher; When away from the observation point, the wavelength becomes longer and the frequency becomes lower. Because of the relative radial motion of the satellite relative to the ground radar, the receiving frequency is different from the transmitting frequency, and the altitude, velocity and azimuth of the satellite can be calculated by changing the frequency. If this method is used for continuous measurement, accurate actual satellite orbit data can be obtained. However, due to the "stationary" characteristics of geostationary satellites, the role of Doppler tracking is not obvious, so the Doppler velocimetry system can not accurately determine the orbit of geostationary satellites. Interferometer system usually needs to combine high-precision radio ranging data, and this orbit determination method can be divided into very long baseline interferometry system and short baseline interferometry system. Very long baseline interferometry system mainly has a baseline length of tens of thousands of kilometers. Use more than two dedicated antennas to alternately receive satellite signals and reference source signals with accurately known orbits near satellites (such as radio sources, deep space vehicles, GPS satellites or other GEO satellites, etc.). ), by measuring the group delay, we can get the position, speed and included angle with the direction of the radio source at the observation time. The positioning accuracy of this method is1~1.5m. The short baseline interferometry system mainly carries out high-precision phase delay observation when the baseline length is within 100 km, and obtains accurate and reliable phase ambiguity. Compared with a long baseline, the construction cost is low and the maintenance is easy. The positioning accuracy is about 5 0 m (2 1km baseline). As the latest technology of radio measurement, interferometer system is getting extensive attention and development. According to the practical work, the determination of satellite orbit is studied theoretically. Through the analysis of the satellite orbit determination methods currently used, it can be seen that these two methods can not meet our work needs. Therefore, in order to put forward a set of technical solutions suitable for our work needs, we must combine the above technical means with our existing work practice. 3. 1 Our existing actual conditions First of all, in terms of the number and location distribution of ground monitoring stations, we can well meet the requirements of satellite orbit determination. There are 9 ground monitoring stations under the National Radio Monitoring Center, including 5 monitoring stations in Beijing, Shanghai, Harbin, Urumqi and Chengdu, and 4 monitoring stations in Shenzhen, Kunming, Xi and Wuyishan, Fujian are under construction. Secondly, in the process of locating satellite interference sources, we actually only need to determine the ephemeris data of neighboring satellites corresponding to the interfered satellites. This is because the satellite company or operator to which the interfered satellite belongs will provide very accurate ephemeris data of the interfered satellite, so that we can quickly find out the specific location of satellite ground interference sources and help them solve their own satellite interference problems. 3.2 Scheme for Determining Satellite Orbit According to the satellite orbit determination method described above, it can be seen that the method of radio ranging for satellites must transmit signals to satellites, which cannot meet our requirements, because we cannot affect the normal work of neighboring satellites. In order not to affect the adjacent satellites, we have to measure the distance difference, that is, multiple ground monitoring stations receive the same signal on the satellite under test at the same time, and then carry out correlation operation on the received signals to find out the distance difference. But this requires all ground monitoring stations to keep strict time synchronization, otherwise the actual distance difference cannot be obtained without the same time standard. It is almost impossible to strictly unify the time standard among multiple ground monitoring stations. Therefore, the problem of time synchronization must be solved first in satellite orbit determination by measuring the distance difference. Combined with the existing known conditions and the current satellite orbit determination technology, the following solutions are proposed. This scheme will realize the adjacent satellite orbit determination task of the interfered satellite. Fig. 2 is a schematic diagram of the orbit determination scheme proposed according to the actual work. Firstly, the frequency of the selected satellite (neighboring satellite) is surveyed, and the satellite signal with appropriate conditions such as frequency, bandwidth and power is selected. According to the specific situation of the satellite, determine a main TT&C station and at least three auxiliary TT&C stations. Then, the satellite signals selected from the satellites are received at these auxiliary TT&C stations respectively. After receiving the signal, the auxiliary TT&C station transmits the signal to the idle frequency band of the corresponding transponder of the interfered satellite with another antenna. At the same time, the main TT&C station can get a time difference, that is, the distance difference, by associating the signals sent by adjacent satellites with the signals forwarded by the auxiliary TT&C stations, so that a three-dimensional equation can be listed, and a set of equations can be established simultaneously by performing the same steps for the three auxiliary TT&C stations. By solving this set of equations, the spatial position of adjacent satellites at a certain moment can be obtained, and then the spatial position of adjacent satellites at multiple moments can be obtained by the same method, so that the speed of satellites can be calculated. After the position and velocity (i.e. motion parameters) of the satellite are obtained, the orbit parameters of the satellite can be determined. This method successfully avoids the requirement of time synchronization for multiple ground TT&C stations, and directly completes signal correlation at the main TT&C station to obtain the required distance difference, thus solving the time synchronization problem. 3.3 Theoretical Basis of Satellite Orbit Determination Scheme First, we know the orbital parameters of the interfered satellite, and then convert the orbital parameters into the motion parameters in IJK coordinate system (geocentric inertial coordinate system), that is, we can calculate the sum of orbital parameters A, E, I, ω, ω and M0 at time t0. After we get the motion parameters of the interfered satellite and add the known geographical coordinates of the ground monitoring station, we can list a set of equations. Details are as follows. Assume that in the geocentric inertial coordinate system (IJK), the geographic coordinates of the main monitoring station are A0(a0, b0, c0), and the auxiliary monitoring station is A 1 (A 1, B 1, C 1), A2(a2, b2, c2). At time t0, the position coordinates of the interfered satellite are P(x0, y0, z0). According to the above conditions, the position coordinates Q(x, y, z) of adjacent satellites at time t0 are obtained. According to the principle of positioning design, the same satellite signal of two satellites received by the main monitoring station can get a time difference, that is, the distance difference, after correlation, which is set as Li. Using the distance relation in IJK coordinate system, we can get the following equation: | qai |+| pai ||| Pa0 |-| qa0 | = li (I = 1, 2,34 ...), and substitute it into the above equation to get: (i =1,2,3,4 ... Similarly, we can monitor the position coordinates of neighboring stars at different times, and thus calculate the velocity parameters of neighboring stars. Using the position and velocity of the satellite in the geocentric inertial coordinate system (IJK), the orbit parameters of the satellite can be obtained. Conclusion From the above analysis, it can be seen that this satellite orbit determination scheme is feasible in theory. It uses the same ground monitoring station to receive satellite signals with the same content from two different satellites for correlation, which skillfully solves the time synchronization problem when receiving satellite downlink signals. Moreover, this satellite orbit determination scheme has no influence on the neighboring star we choose, and it is completely determined without the other party's knowledge. This will not affect the normal work of neighboring satellites, but also meet our orbit determination work for the ground interference sources of the interfered satellites, which is another great advantage. However, the satellite orbit determination scheme is a theoretical idea put forward in an ideal situation, which will definitely introduce various errors in the specific operation. At the same time, the satellite company to which the interfered satellite belongs needs strong cooperation, especially there should be an idle frequency band on the corresponding transponder of the interfered satellite to ensure that the signals received by the auxiliary TT&C station from neighboring satellites can be forwarded to the main TT&C station through this frequency band. As mentioned above, this scheme may encounter some difficulties in practical operation, but it is proved to be feasible in theory. It is believed that through the continuous improvement and supplement of specific experiments, this theoretical idea will definitely become a mature operating procedure, and the problem of obtaining satellite ephemeris will definitely be solved.