ISRO conducts controlled re-entry tests of old satellites

Controlled re-entries involve deorbiting at a very low altitude to ensure impact occurs within a safe zone

Bangalore:

The Indian Space Research Organization said it successfully conducted a “highly challenging” controlled re-entry test of the decommissioned orbiting Megha-Tropix-1 (MT-1) satellite on Tuesday.

“The satellite has re-entered Earth’s atmosphere and will disintegrate over the Pacific Ocean,” the Bengaluru-headquartered National Space Agency said on Twitter.

The controlled re-entry test for the decommissioned Megha-Tropics-1 (MT-1) was successfully completed on March 7, 2023.

The satellite re-entered Earth’s atmosphere and disintegrated in the Pacific Ocean. pic.twitter.com/UIAcMjXfAH

— ISRO (@isro) March 7, 2023

The final impact zone is estimated to be in the deep Pacific Ocean within the expected latitude and longitude boundaries, an ISRO statement said.

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

Since August 2022, the satellite’s perigee has been progressively lowered through a series of 20 maneuvers consuming about 120 kg of fuel.

Multiple strategies, including the final de-boost strategy, were designed considering various constraints, including visibility of the reentry trace over ground stations, ground effects within the target area, and allowable operating conditions of the subsystems, particularly the maximum deliverable thrust and. Thruster maximum firing duration limitation.

All maneuver plans were screened to ensure that no maneuver followed a close approach with other space objects, particularly crewed space stations such as the International Space Station and the Chinese Space Station, ISRO said.

The final two D-boost burns were fired at the satellite at 11:02 UTC and 12:51 UTC on March 7, with four Newton thrusters firing at the satellite for about 20 minutes, it said.

The final perigee was estimated to be less than 80 km indicating that the satellite would enter the dense layer of Earth’s atmosphere and subsequently undergo structural disintegration. Re-entry aero-thermal flux analysis confirmed that no large debris fragments survived.

The entire sequence of events was executed from the Mission Operations Complex at ISTRAC (ISRO Telemetry, Tracking and Command Network), Bangalore.

An uninhabited area in the Pacific Ocean between 5°S to 14°S latitude and 119°W to 100°W longitude was identified as the targeted re-entry zone for MT1, weighing around 1000 kg, ISRO said earlier this week.

Around 125 kg of on-board fuel remained unused at the end of the mission which could pose a risk for accidental separation, an ISRO statement noted.

This remaining fuel was estimated to be sufficient to achieve fully controlled atmospheric re-entry to impact uninhabited locations in the Pacific Ocean, ISRO said.

Controlled re-entries involve deorbiting at a very low altitude to ensure impact occurs within a targeted safe zone.

Generally, large satellite/rocket bodies, which are likely to survive aero-thermal fragmentation after re-entry, undergo controlled re-entry to limit the risk of ground accidents.

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

“MT-1 was not designed for EOL operation through controlled re-entry which made the whole exercise extremely challenging”, ISRO said.

Furthermore, the on-board limitations of aging satellites, where several systems have lost redundancy and have shown degraded performance, and maintaining subsystems in environmental conditions much lower than originally planned orbital altitudes added to operational complexity, it said.

Innovative solutions were implemented by operations teams based on studies, discussions, and exchanges among mission, operations, flight dynamics, aerodynamics, propulsion, control, navigation, thermal, and other sub-system design teams across ISRO centers, who worked to address these challenges. Simultaneously to do, it said.

Although the satellite’s mission life was originally three years, it has continued to provide valuable data services for over a decade, supporting regional and global climate models till 2021, ISRO said.

The UN/IADC (Inter-Agency Space Debris Coordination Committee) space debris mitigation guidelines recommend deorbiting a LEO (Low Earth Orbit) object at its EOL, preferably by controlled re-entry into a safe impact zone, or bringing it into orbit. According to ISRO, the orbital lifetime is less than 25 years.

“Passivation” of on-board power sources is also recommended to reduce the risk of accidental break-up post-mission, it said.

MT-1 will have an orbital lifetime of more than 100 years in its 20-degree inclined operational orbit at an altitude of 867 km, according to ISRO.

“As a responsible space organization committed to safe and sustainable operations in outer space, ISRO actively undertakes efforts for better compliance with the UN/IADC space debris mitigation guidelines for post-mission disposal of LEO objects”, the ISRO statement said.

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