Explained: European Space Agency to help India 'see and speak' to Gaganyaan

Chennai, India

In the coming years, when India's Gaganyaan astronaut-carrying capsule circles the Earth, antennae belonging to the European Space Agency (ESA) will help the Indian Space Research Organization (ISRO) 'see and speak' to the mission.

ISRO and ESA signed a Technical Implementing Plan (TIP) document for Ground Tracking Support for Gaganyaan Missions. The TIP was signed by Dr Anilkumar A K, Director, ISTRAC, from ISRO and Mr Dietmar Pilz, Director of Technology, Engineering & Quality and Director of ESTEC, Netherlands, from ESA.

The TIP was signed at the Indian Spaceport, Satish Dhawan Space Centre (SDSC), in the presence of Dr S Somanath, Chairman, ISRO and Mr Didier van der Hasselt, Belgium's Ambassador to India.

What is a satellite ground station and how does it work?

A satellite ground station is an Earth-based facility equipped with antennae, specialised hardware and software that help communicate with satellites in space. These stations serve as the bridge between space assets and Earth, enabling the exchange of data, commands, and signals.

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Satellites and ground stations communicate via radio waves, which require a clear line of sight. Due to Earth's curvature, a ground station (antenna) can maintain contact with a satellite only while the satellite is above the station's field of view. As satellites orbiting the earth only spend a couple of minutes within the range of an antenna, a network of ground stations around the globe is required to maintain continuous contact with the satellite. 

Therefore, as India's Gaganyaan astronaut-carrying capsule circles the Earth, multiple ground stations around the world will help Indian ground controllers stay in touch with the crew, monitor the spacecraft, and its technical parameters, and carry out many crucial functions. Establishing multiple ground stations around the world is a very expensive and time-consuming effort, which is why space agencies collaborate and share their tracking resources.

Telemetry, Tracking, and Command (TT&C)

Ground stations are used to monitor the satellite's health, such as power levels, orientation (which direction it is facing), and system status. This process is known as Telemetry. 

Satellites have to remain in a specific pre-determined orbit to carry out their functions. Ground stations are responsible for keeping a tab on the satellite's orbit, a function that is known as Tracking. 

Satellites carry various payloads (scientific equipment) onboard and each one of them has a unique purpose and function. Ground stations regularly issue commands to satellites to perform specific tasks – such as clicking pictures of a certain region, operating a particular piece of equipment, manoeuvring the satellite in a certain direction etc. Simply put, it is a process of remotely controlling the satellite, based on instructions issued from the ground. 

Global support for tracking India's Chandrayaan-3

ISRO Telemetry, Tracking and Command Network (ISTRAC) in the city of Bengaluru handles the major responsibility of providing tracking support for all the satellite and launch vehicle missions of ISRO. ISTRAC has a network of ground stations at Bengaluru, Lucknow, Sriharikota, Port Blair, and Thiruvananthapuram, within India.

Brunei, Biak (Indonesia), and Mauritius are the friendly-foreign nations where ISTRAC operates its overseas facilities. However, when a spacecraft like Chandrayaan-3 circles the Earth and travels farther (the moon is 3.84 lakh km away), it is imperative to have a global network of stations that can offer tracking support.

As part of ISRO's international cooperation with major space agencies, multiple tracking stations belonging to NASA, the European Space Agency and the Swedish Space Corporation tracked Chandrayaan-3 from around the world. These include South Point Satellite Station in Hawaii, Goldstone in California, Kourou in South America (French Guiana), Madrid in Spain, Goonhilly in the United Kingdom and Canberra in Australia. The constant tracking from Indian and foreign stations ensured that India's Chandrayaan-3 spacecraft was visible to one or more stations at a time and could be monitored and safely steered towards the Moon.

Ship-based tracking

There are times when the rocket is not 'visible' to tracking antennae, especially, when the rocket or satellite flies over the high seas, where tracking stations are unavailable. Such gaps in the tracking process are filled in by specialised tracking ships that are fitted with long-range radars and communications antennae. 

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Such vessels are stationed at a pre-determined location on the high seas, by the flight path of the rocket/satellite. As the vehicle overflows that large region, the sensors and tracking equipment on board the ship can provide real-time tracking and telemetry on how the mission is progressing.  

In October 2022, when ISRO launched 36 satellites of the European firm OneWeb, India positioned Ocean Research Vessel Sagar Nidhi in the Indian Ocean region (thousands of kilometres south of India's southern tip) to track the flight of the LVM3 rocket that was flying towards the south pole. 

International Cooperation for Gaganyaan tracking

In close coordination with the Australian government and space agency, ISRO will be setting up a tracking antenna at the Australian External Territory of Cocos Keeling islands, to track the Gaganyaan craft, as it overflies the region. Similarly, Indian and Australian authorities have signed a pact to ensure support for the search and rescue of crew, and recovery of crew module as part of contingency planning (in case the Gaganyaan crew module has to be ejected mid-flight). This arrangement is in place, as the ejected capsule could land in Australian waters.

ISRO and ESA have signed the Technical Implementing Plan (TIP) so that ISRO can avail the support of ESA's tracking station network Estrack. Estrack is a global system of ground stations providing links between satellites in orbit and the European Space Operations Centre (ESOC), Darmstadt, Germany. The core Estrack network comprises seven stations in seven countries. The essential task of all ESA ground tracking stations is to communicate with spacecraft, transmitting commands and receiving scientific data and spacecraft status information.