ISRO brings down decommissioned weather satellite Megha-Tropiques-1

After the final two manoeuvres on Tuesday evening – firing four onboard thrusters for around 20 minutes each – the satellite entered the denser atmosphere and disintegrated over the Pacific Ocean.

Large satellites likely to survive re-entry through the atmosphere and shower down debris are brought down in a controlled manner to ensure that it does not impact people.

Megha-Tropiques-1 was developed as a joint mission by India and France to study the tropics’ water cycle and energy exchanges. Like many others developed by the ISRO, the satellite worked for over a decade, providing valuable data for climate models. The 1,000-kg satellite was launched in 2011 with a mission life of three years.

The space agency said that the de-boost manoeuvres were planned considering several constraints, such as the re-entry being visible from the ground stations, ground impact in the targeted zone, and maximum thrust and maximum firing duration of the thrusters.

“All manoeuvre plans were screened to ensure that there would be no post manoeuvre close approaches with other space objects, especially with the crewed space stations like International Space Stations and the Chinese Space Station,” the space agency said in a release.

The space agency said satellites such as Megha-Tropiques-1 were not designed to undergo such controlled re-entry after the end of life, making it challenging. Complicating matters further was that the satellite had been sitting in orbit longer and lower than intended, which meant several systems had lost redundancies and their performance had degraded.

“Innovative workarounds were implemented by the operations … teams across the ISRO centres, who worked in synergy to surmount these challenges.”

The space agency added, “In recent years, ISRO has taken up proactive measures to improve the compliance level with the internationally accepted guidelines on space debris mitigation.” This will ensure that the lower earth orbit, where most satellites are placed, doesn’t get overcrowded and that satellites are disposed of safely.

The space agency said the United Nations and Inter-Agency Space Debris Coordination Committee (IADC) guidelines recommend that satellites be deorbited – either through controlled entry over a safe impact zone as was attempted by Isro with Megha-Tropiques-1 or by bringing it down to reduce the orbital lifetime – the time it would take for a satellite to drop from a particular orbit by itself – to less than 25 years.

It is also recommended that stored fuel be removed from the spacecraft to ensure that no accidents break up the satellite in space and create more debris.

In the case of Megha-Tropiques-1, the orbit of 867 km with 20-degree inclination meant an orbital lifetime of over 100 years. And over 120 kg of fuel was left over, which was estimated to be sufficient to achieve a fully controlled atmospheric re-entry.

The space agency said, “The re-entry experiment of MT1 has been undertaken as a part of the ongoing efforts as this satellite with sufficient left-over fuel presented a unique opportunity to test the relevant methodologies and understand the associated operational nuances of post-mission disposal by direct re-entry into the earth’s atmosphere.”