TELEMETRY, TRACKING, COMMAND AND MONITORING SYSTEM IN GEOSTATIONARY SATELLITE Alish 1, Ritambhara Pandey 2 1, 2 UG, Department of Electronics and Communication Engineering, Raj Kumar Goel Institute of Technology for Women, Ghaziabad (India) ABSTRACT The Telemetry system sends data derived from many sensors on the satellite, which monitor satellite s health; via a telemetry link to the controlling earth station. These systems are partly on the satellite and partly at the controlling earth station. The tracking system is located at this earth station and provides information on the range and the elevation and azimuth angles of the satellite. Based on telemetry data received from the satellite and orbital data obtained from the tracking system, the control system is used to correct the position and attitude of the satellite.it is also used to control the antenna pointing and communication system configuration to suit current traffic requirements, and to operate switches on the satellite. I. INTRODUCTION The TTC & M system is essential to the successful operation of a communication satellite and sends this data to the controlling earth station. Satellite management has various quality of controlling the task which are totally dedicated to that particular work and it also has a group of personnel. The telemetry, tracking and control subsystem provides various essential communication to and from the space vehicle. The main functions of a satellite management are to control the orbit and attitude of the satellite, monitor the status of all sensors and subsystems on the satellite, and the measurement describes the satellite, subsystem by subsystem. These measurements takes into account magnitude which varies with different parameters which varies in terms of voltage and current. II. TELEMETRY AND MONITORING SYSTEM The monitoring system has an ability of collecting the data obtained from many sensors within the satellites and after observing it, sends these data to the controlling earth station. There may be several hundred sensors on the satellite which are used in the monitoring of various parameters such as pressure, voltage and current in the power conditioning unit, which draw the voltage and currents in the communication electronics. The temperature of many subsystems must be kept within predetermined limits as it is the most important parameter in communication systems. The sensor data and the status of each subsystem, can be reported back to the earth by the telemetry 261 P a g e
system. Telemetry data are usually digitized and transmitted as phase shift keying (PSK) of a low-power telemetry carrier using time division techniques. The entire TDM frame may contain thousands of bits of data and take several seconds to transmit. The controlling earth station performs the function of monitoring, storing and decoding the data so that the status of any system or sensor on the satellite can be determined immediately by the controller on the earth. Fig1: Typical Tracking, Telemetry, Command and Monitoring System. III. TRACKING A number of techniques can be used to determine the current orbit of a satellite. The current position of an orbit can be determined by integrating the data obtained by velocity and acceleration sensors. The earth station controlling the satellite can observe the Doppler shift of the telemetry carrier or beacon transmitter carrier to determine the rate at which range is changing. The range obtained from angular measurements from the earth station is capable of determining the orbital elements.a pulse or a sequence of pulses is transmitted to the satellite and time delay before the pulse is received is observed to calculate active range. Triangulation method is used to determine the position of a satellite when a sufficient number of earth stations are observing it. Ranging measurements can also be done using Ranging tones. A series of increasing frequency sine waves are used to modulate the onboard generated carrier. The number of wavelengths of each frequency can be obtained by comparing the phase of modulating component of sine 262 P a g e
wave. For the determination of exact orbital position of the satellite the elevation and azimuth angle measurements are very important. Fig 2: Satellite in an inclined orbit IV. COMMAND A reliable and effective command structure is essential for the successful launch and operation of any communication satellite. The correction to the orbit and changes in the attitude is done by the command system. During launch, it is used to control the firing of the apogee kick motor and to spin up a spinner or extend the solar sails and antennas of a three-axis stabilized satellite. Encryption of commands and responses is used to provide security in the command system. First of all the control code is converted into a command word and sent to the satellite in a TDM frame. The command and telemetry links can operate in the same frequency band (6 and 4 GHz) but they are usually separated from the communication system. In case the main TTC & M system fails, the backup system is used to keep the satellite on station. It is also used to eject the satellite from geostationary orbit. Fig 3: Control Panel. 263 P a g e
Fig 4: TTC& M Satellite V. TT&C Interferences Subsystem Requirement Attitude determination and control Antenna pointing Command and data handling Command and telemetry data rates Clock, bit sync and timing requirements, Two-way communication requirements, Autonomous fault detection and recovery, Command and telemetry electrical interface. Electrical Power Subsystems Distribution requirements Thermal/Structural Heat sinks for TWTAs, Heat dissipation for all active boxes, Location of TT&C subsystem electronics, Clear field of view for all antennas. Payload Storing missing data, RF and EMC storage requirements, Special requirements for modulation and coding. VI. TT&C Trade offs 1. Antenna size vs transmitted power. 2. Solid state amplifiers vs travelling wave tube amplifiers. 264 P a g e
3. Spacecraft complexity vs ground complexity. VII. CONCLUSION After studying the TTC&M satellite system thoroughly we concluded that the satellite must carry a number of subsystem to support its communications mission. The attitude and orbital control system keeps the satellite in the correct orbit. The Telemetry, Tracking, command and monitoring system allows and earth station to control the subsystems in the satellite and to monitor their health. Solar cells are used to generate the electrical power, batteries provides essential power during launch and eclipses. Satellites often employ frequency reused that can allow the same RF spectrum to be used more than once to increase the satellite s capacity. Antennas are a limiting factor in all radio communication system. Reliability is an another important issue in satellite. Additional receiver and high power amplifier that can take over when a unit falls is provided by redundancy. REFERENCES [1] WALTER L. MORGAN, GARY D. GORDAN, Communication satellites handbook, Wiley Interscience, New York, 1989. [2] TIMOTHY PRATT, CHARLES BOSTIAN, JEREMY ALLNUTT, Satellite Communications, second edition, Virginia Polytechnic Institute and State University, George Mason University, 2011(Reprint). [3] W.H. BRAUN and J.E. KEIGLER, RCA Satellite Networks: High Technology and Low User Cost, Proceedings of the IEEE, 72, 1483-1505, November 1984. [4] www.astrolink.com [5] www.hns.com.spaceway [6] Pisacane, Vincent L. and Robert C. Moore (1994); Fundamentals Of Space Systems, Oxford University Press, New York, 1994. 265 P a g e