ISRO carries out controlled re-entry of aged satellite

• The Indian Space Research Organisation (ISRO) successfully carried out a controlled re-entry experiment of the decommissioned orbiting Megha-Tropiques-1 (MT-1) satellite.

• The satellite re-entered the Earth’s atmosphere and the final impact region estimated is in the deep Pacific Ocean within the expected latitude and longitude boundaries.

• The low Earth satellite was launched on October 12, 2011, as a joint satellite venture of ISRO and the French space agency, CNES for tropical weather and climate studies.

Why ISRO took up this challenging experiment?

• Although the mission life of the satellite originally was three years, it continued to provide valuable data services for more than a decade supporting regional and global climate models till 2021.

• The orbital lifetime of MT-1, weighing about 1,000 kg, would have been more than 100 years in its 20-degree inclined operational orbit of 867 km altitude. 

• About 125 kg on-board fuel remained unutilised at its end-of-mission that could pose risks for accidental break-up

• UN/IADC space debris mitigation guidelines recommend deorbiting a Low Earth Orbit (LEO) object at its end-of-life, preferably through controlled re-entry to a safe impact zone, or by bringing it to an orbit where the orbital lifetime is less than 25 years.

• It is also recommended to carry out “passivation” of on-board energy sources to minimise the risk of any post-mission accidental break-up.

• As a responsible space agency committed to safe and sustainable operations in outer space, ISRO proactively takes efforts for better compliance with the UN/IADC space debris mitigation guidelines on post-mission disposal of LEO objects.

• The re-entry experiment of MT-1 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.

• Controlled re-entries involve de-orbiting to very low altitudes to ensure impact occurs within a targeted safe zone.

• Usually, large satellites/ rocket bodies, which are likely to survive aero-thermal fragmentation upon re-entry, are made to undergo controlled re-entry to limit ground casualty risk.

• However, all such satellites are specifically designed to undergo controlled re-entry at end-of-life (EOL).

• MT-1 was not designed for EOL operations through controlled re-entry which made the entire exercise extremely challenging.

How was it executed?

• Since August 2022, the satellite’s perigee was progressively lowered through a series of 20 manoeuvres, spending about 120 kg of fuel.

• Multiple manoeuvres including the final de-boost strategy were designed after taking into consideration several constraints, including visibility of the re-entry trace over ground stations, ground impact within the targeted zone, and allowable operating conditions of subsystems, especially the maximum deliverable thrust and the maximum firing duration constraint on 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 final two de-boost burns were executed at 11:02 UTC (Coordinated Universal Time) and 12:51 UTC respectively on March 7 by firing four 11 Newton thrusters on-board the satellite for about 20 minutes each.

• The final perigee was estimated to be less than 80 km, indicating that the satellite would enter the denser layers of the Earth’s atmosphere and subsequently undergo structural disintegration. 

• The re-entry aero-thermal flux analysis confirmed that there would be no surviving large debris fragments.

• The entire sequence of events was carried out from the Mission Operations Complex in ISTRAC (ISRO Telemetry, Tracking and Command Network), Bengaluru.

• An uninhabited area in the Pacific Ocean between 5S to 14S latitude and 119W to 100W longitude was identified as the targeted re-entry zone for MT1, weighing about 1,000 kg.

• About 125 kg on-board fuel remained unutilised at its end-of-mission that could pose risks for accidental break-up. This left-over fuel was estimated to be sufficient to achieve a fully controlled atmospheric re-entry to impact the uninhabited location in the Pacific Ocean.

Manorama Yearbook app is now available on Google Play Store and iOS App Store