ISRO Telemetry, Tracking and Command Network (ISTRAC) headquartered in Bengaluru provides tracking support for satellites and space missions launched from India. ISTRAC’s telemetry, tele-command network includes ground stations in Bangalore, Thiruvananthapuram, Lucknow and Port Blair in India. It also operates stations overseas in Mauritius, Bearslake (Russia), Biak (Indonesia), and Brunei. Those in Thiruvananthapuram and Mauritius have served as down-range stations for PSLV missions. ISTRAC maintains high-reliablity links with INSAT’s and INTELSAT satellites for communication worldwide. A new satellite tracking center is also set to be operationalized in Vietnam this year augmenting ISTRAC’s tracking capabilities.
The satellites that are monitored and controlled from Bangalore are: IRS-1C and 1-D, P-3, P-4 and P-6, all of which are used for remote sensing, besides the Technology Experiment Satellite (TES) and Cartosat-1 and -2. They are monitored 24 hours a day through out the year. Teams of specially trained young people keep a vigil and correct the path of satellites, when needed, under the guidance of experts. What is more remarkable is the fact that the entire software for control and monitoring of the satellite has been developed in house by ISRO.
A satellite typically passes over India in about 7 minutes. In fact, a satellite is watched for a total of about 35 minutes, as other stations besides Bangalore, are in contact with it from Mauritius, Biak (Indonesia), Bearslake (Russia) and Lucknow. The data gathered from these stations well as the data collected and stored when the satellite is out of reach of these stations is made available to the ground control in Bangalore. Today, a satellite can certainly be watched in 13 out of 14 orbits a day.
Typically a satellite is designed to follow an orbital path within a very narrow corridor. A difference of just 1º in the pointing accuracy at a height of 600 km will result in a difference of 10 km on the ground. The satellite’s positioning accuracy, achieved by the Indian team, has improved dramatically over the years, starting from 0.3º in IRS-1A and -1B to 0.15º in IRS-1C, reaching 0.02º in P-6 (Resourcesat-1), launched in 2003. The path of P-6 is known within 240 meters of the nominal, mainly because of an innovation called ‘star sensors’, which helps determine the path by its orientation with the position of selected stars in the sky.
IRS-P6 has another innovation on board, it is integrated with the Global Positioning System, which itself ascertains the position of the satellite within 25 meters, as against 80 meters obtained manually by ground-based ranging calculations. The satellite’s health is monitored closely.
Its temperature, pressure, the power available in the battery and the solar panels, the status of the gyroscopes and the payload, etc. are registered and compared with the nominal values. Computers observe close to 1,000 parameters. Any deviation is indicated by a red blinking square on the computer screen. The ground controllers ignore the ones they know are not crucial or permanent but by force of habit pounce on those that are critical for the success of the satellite.
NASTRAC (Nitte Amateur Satellite Tracking Centre) was setup in 2010 to monitor Pico and Nano-satellites in Bangalore. There also exist many other small private trackers hosted by engineering colleges across South India.