6.03.2023

The Indian Space Research Organization (ISRO) is gearing up for a challenging experiment of controlled re-entry of decommissioned satellite Megha-Tropiques-1 (MT1) into low Earth orbit on March 7. MT1 was launched on October 12, 2011. As a joint satellite venture of ISRO and French space agency CNES for tropical weather and climate studies.

Although the satellite’s mission life was originally three years, the satellite will continue to provide valuable data services for over a decade, supporting regional and global climate models until 2021, the Bengaluru-headquartered space agency said in a statement on Sunday. Said. The UN/IADC (Inter-Agency Space Debris Coordination Committee) space debris mitigation guidelines recommend deorbiting a LEO (Low Earth Orbit) object at its end of life (EOL), preferably a controlled re-entry into a safe impact zone. Through entry, or according to ISRO, by bringing it into an orbit where the orbital lifetime is less than 25 years.

A “deactivation” of the on-board power sources is also recommended to reduce the risk of any post-mission accidental break-up. The orbital lifetime of MT1, weighing about 1,000 kg, would have been more than 100 years in a 20° inclined operational orbit of an altitude of 867 km. About 125 kg of on-board fuel remained unusable at the end of its mission which could pose a risk for an accidental break-up. This leftover fuel was estimated to be sufficient to achieve a fully controlled atmospheric re-entry to impact an uninhabited location in the Pacific Ocean.

Controlled re-entry involves deorbiting at a very low altitude to ensure impact within the target safe zone. Generally, large satellite/rocket bodies that are likely to survive air-thermal fragmentation on re-entry undergo controlled re-entry to limit ground casualty risk. However, all such satellites are specifically designed to undergo controlled re-entry at EOL. MT1 was not designed for EOL operation via controlled re-entry, which made the entire exercise extremely challenging.

In addition, the on-board constraints of an aging satellite, where many systems had lost redundancy and showed poor performance, and maintaining subsystems in harsh environmental conditions far below the originally designed orbital altitude added to operational complexities. were added.

Innovative solutions were implemented by the operations team based on studies, deliberations and exchanges between mission, operations, flight dynamics, aerodynamics, propulsion, control, navigation, thermal and other subsystem design teams at ISRO centres, which worked in synergy Work done. To overcome these challenges.

An uninhabited region in the Pacific Ocean between 5°S to 14°S latitude and 119°W to 100°W longitude was identified as the target re-entry zone for MT1. From August 2022, 18 orbit maneuvers were carried out to progressively lower the orbit. In between de-orbiting, aero-braking studies were also carried out at different solar panel orientations to gain better insight into the physical process of atmospheric drag affecting the satellite’s orbital decay.

Formulated the final de-boost strategy taking into account several constraints, including visibility of the re-entry trace at ground stations, ground effects within the target area, and acceptable operating conditions of subsystems, in particular maximum deliverable thrust and maximum Has been. Firing duration of thrusters.

The final two D-boost burns are expected after ground impact between 16.30 hours and 19.30 hours on March 7. Simulations suggest that any large fragments of satellites are unlikely to have survived aerothermal heating during re-entry. “As a responsible space agency committed to safe and sustainable operations in outer space, ISRO actively strives for better compliance with the UN/IADC space debris mitigation guidelines,” the statement said.

The re-entry experiment of MT1 has been carried out as part of the ongoing effort as the satellite with sufficient fuel left has been used to test relevant functionality and understand the operational nuances related to post-mission disposal by direct re-entry. presented a unique opportunity. Earth’s atmosphere, it was said.

Quelle:BHARAT TIMES