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GEO satellite orbital inclination change Da Houtian Line Tracking Method

In Electronic Infomation Category: G | on April 15,2011

in the use of a GEO satellite network applications, the satellite signal receive antenna with 13 m truss to step way to track the satellite. GEO satellite orbit inclination as small (theoretical value 0), the actual work on a regular basis to maintain the angle control through North-South a lesser extent, so truss satellite tracking antenna to work properly. GEO satellites into life when the late star on the fuel shortage, in order to save fuel, stop the North and CY7C157-20JC datasheet and the South to maintain control of the satellite, leading to the satellite orbital inclination becomes larger and CY7C157-20JC price and larger, step tracking mode can not properly track the satellite, resulting in some important parameters of the system can not meet the system design specifications, of the system to provide normal service.

1 step tracking mode

truss antenna step tracking is a way to track satellites, the method based on GEO satellite telemetry signal in the AGC level to determine if the antenna is aligned satellite. When the AGC level telemetry data below the set value, the antenna means to step up and CY7C157-20JC suppliers and down about 4 to adjust the antenna pointing direction and to monitor whether the peak AGC level, if it reaches the peak, that * line has been aligned satellite.

satellite transponder channel spiral current of the station is aimed to determine whether the satellite antenna and satellite signals from stations within range of the signal beam quality is an important parameter, when the antenna is accurately aimed at the satellite, spiral flow values remained stable. GEO satellite orbit inclination with further larger, the antenna will result when each adjustment screw flow fluctuations, Figure 1 is a satellite antenna step track mode after the spiral flow angle larger changes in the day.

Figure 1 step tracking mode changes in the satellite channel spiral flow chart

2 program tracking mode

step tracking mode for the shortcomings, a process control method of satellite tracking antenna, called a program tracking.

the method using satellite ephemeris information in calculating the satellite position to point the antenna, the azimuth and elevation, and the form of instructions to drive the antenna control unit (OCU) control of the antenna tracking the satellite.

The method uses orbital inverse method, based on satellite ephemeris accurate calculation of the ground antenna pointing in the implementation process in which two key problems to be studied and solved, namely the calculation of antenna pointing control the antenna satellite tracking strategy.

system uses satellites in geosynchronous orbit, so first consider the use of geostationary satellite ground antennas formula to calculate the ground antenna pointing. In calculating the antenna pointing process, known quantity of satellite ephemeris data and antenna position in the satellite latitude and longitude location of surface.

known quantity: the satellite ephemeris data, satellite position information X, the satellite Y Z position information and satellite position information of three parameters; ground position ground antenna system location of latitude and longitude.

(1) calculating the satellite longitude

satellite nadir Longitude:

(2) calculating the ground antenna pointing

aligned geostationary satellite earth station antenna main beam while the azimuth and elevation calculation formula: Let A ground station latitude and longitude for the 1 and 1, geostationary satellite nadir S, S The latitude and longitude for the 2 and 2.

= 2 - 1 to the nadir S A of the earth station longitude difference. RE is the Earth radius (6 378 km); hE satellite height above the ground; A for the earth station and satellite point S in the Earths surface by a large arc angle of the center of the earth.

geometry and spherical trigonometry using some of the basic formula is not difficult to calculate: if aimed at the satellite station antenna A S, its elevation e, azimuth difference a and longitude , ground station 1 as a function of latitude:

using spherical trigonometry law of cosines can get:

so you can get:

geostationary satellite for the purposes of:

aligned according to the geostationary satellite earth station antenna main beam while the azimuth and elevation calculation formula can be identified:

azimuth is calculated as:

pitch angle is calculated as follows:

the antennas azimuth and elevation values, the value of solving the amended access and step tracking antenna pointing data for comparison and found that the accuracy can reach 0. 1 , can not meet requirements.

analysis and testing through further research and found that the problem is due to larger GEO satellite orbit inclination, the satellite orbit inclination beyond normal working hours geostationary orbit satellite design requirements, so the research will be needed in the satellite view for non-geostationary orbit satellite, in this context of antenna pointing calculation.

set e for antenna elevation angle, a azimuth for the antenna, which is calculated as:

use this formula calculating the antenna pointing to the data obtained with the actual antenna pointing data for comparison, the data precision is 0. 01 , to meet the requirements.

this formula, due to the use of the satellite nadir by the dimension, the first coordinate conversion to the use of satellite ephemeris data into BLH XYZ coordinates. Calculated as follows:

where, N is ellipsoid prime vertical radius of curvature; e is the first ellipsoid eccentricity; a, b is the length of the radius of the ellipsoid; f elliptical flat rate; W as the first secondary factor.

3 antenna tracking strategy

main strategies of the antenna tracking antenna pointing instructions adjust the transmission time. Step tracking mode to adjust the discrimination based on a 2:

first pre-set tracking frequency, when the node reaches the set time, the step-tracking; the second is when the AGC level is below the threshold, the step-tracking . Geostationary satellite relative to the GEO, in the small angle deviation from a period of time, thus setting the frequency of 30 min will be able to better ensure that the satellite tracking antenna. AGC voltage in the orbital inclination is relatively small with a relative stability, after the satellite angle larger fluctuations, resulting in frequent start stepping tracking system, 30 min interval of the frequency stability can not meet the requirements of the system, and 13 m truss antenna frequency antenna tracking the satellite will increase wear and reduce the antenna life. Therefore, the frequency of the antenna to adjust the number of settings need to consider the contradiction between the system stability. Adjusted too frequently, will increase the wear truss antenna; if to adjust the time interval is too large, then the stability of the system parameters, the system can not stabilize the work, in order to solve this problem, make use of program tracking, and control the frequency of stalls combined degree of control mode. Stall means: , which AZ calculated for the azimuth angle difference with the actual values, EL calculated value for the pitch angle difference between the actual value. Deviation from the stalls and the satellite antenna beam angle on the acceptable deviation, ie deviation from the satellite antenna beam satellite reception caused by the degree of acceptability of the power down. Based on characteristics of the antenna, the antennas 3 dB half-beam width of 0112 , 2 dB half-beam width is 0110 , 1 dB half-beam width is 0108 . If the threshold is set to 0112 , 0110 or 0108 , the corresponding satellite uplink power down 3 dB, 2 dB, 1 dB. Control the frequency of the antenna to adjust the time intervals, depending on the state of the satellite to determine the frequency of different control and the control of the experiment to find the best frequency.

in the tracking process, the antenna pointing data, real-time feedback to the network control software, and solution data calculated antenna pointing calculation stalls, combined with the formation of the frequency control strategy. Control process shown in Figure 2.

Figure 2 program tracking control process

the above analysis, the use of 0. 08 , 0. 10 , 0. 12 3 stalls for tracking test, the fastest frequency adjustment of the antenna were 10 min / times , 13 min / times, 15 min / times, in order to reduce the wear on the antenna, select 0. 15 , 0. 12 to test the two stalls.

(1) stall is 0. 15

spiral flow values of the satellite maximum 3. 24 mA, a minimum of 1. 1 mA. Another spiral flow channel maximum value of 3. 75 mA, a minimum of 1. 00 mA.

satellite over the equator from north to south when the maximum rate of change of spiral flow, adjust the frequency of the antenna for the 16 min / times. Schematic diagram of spiral flow changes during the test shown in Figure 3.

Figure 3 stall 0. 15 change in the day when the spiral flow chart

(2) stalls to 0. 12

spiral flow values of the satellite maximum 3. 24 mA, a minimum of 2. 02 mA.

spiral flow values of the other channel maximum 3. 75 mA, a minimum of 1. 7 mA.

satellite over the equator from north to south to adjust the frequency of the antenna for the 13 min / times.

spiral flow changes during the test diagram shown in Figure 4.

Figure 4 stall 0. 12 change in the day when the spiral flow chart

tracking test comparing the 2, small stalls, day wire.

system of frequent, small spiral flow change interval. In order to ensure the stable operation of the system, screw the flow value is greater than 2. 00 mA. For the current satellite orbital inclination, through testing to determine stall 0. 08 , time 20 min as the best frequency of adjustment strategies.

4 test results

before the test part of the antenna control system functions and software modifications to enable it to track the adoption process approach, and then raised above the truss antenna tracking and access systems with the program realization. After testing, the system spiral flow, AGC voltage and other parameters working properly, significantly reduced the number of antenna adjustment, each time when the satellite antenna tracking control can be in one step. Stall is set to 0. 08 during the day to track changes in Figure 5.

Figure 5 stalls 0. 08 change in the day when the spiral flow chart

5 Conclusion

GEO satellite orbit inclination angle increases, the satellite helix current of a larger range of parameters such as daily changes, jitter is serious, about 20 min a spiral flow of ultra-low alarm (the alarm threshold 2. 0 mA .) Antenna tracking mode using the existing procedures change after the interval spiral flow was convergent, and there is no significant jitter. Significantly reduced the number of antenna adjustment and an adjustment in place to improve the life of the antenna. Especially in the satellite orbit inclination more than 2. 5 case, the use of the method is still able to meet the satellite tracking antenna design the right indicators to ensure that the system is stable and reliable operation of the satellite end of life.

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