BENGALURU: Isro is gearing up for a challenging experiment of controlled re-entry of a decommissioned low Earth orbiting satellite — Megha-Tropiques-1 (MT1) — on March 7. MT1 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.
As per the space agency, an uninhabited area in the Pacific Ocean between 5°S to 14°S latitude and 119°W to 100°W longitude has been identified as the targeted re-entry zone for MT1. And, since August 2022, 18 orbit manoeuvres have been performed to progressively lower the satellite’s orbit.
The final two de-boost burns followed by the ground impact are expected to take place between 4:30pm and 7:30pm on March 7 and Isro said aero-thermal simulations have show no large fragments of the satellites are likely to survive the aerothermal heating during the re-entry.
“Although the mission life originally was up to three years, the satellite continued to provide valuable data services for more than a decade supporting regional and global climate models till 2021,” Isro said.
The UN inter-agency space debris co-ordination committee (IADC) space debris mitigation guidelines recommend de-orbiting 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.
“The orbital lifetime of MT1, weighing about 1,000kg, would have been more than 100 years in its 20 deg inclined operational orbit of 867 km altitude. About 125kg 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 an uninhabited location in the Pacific Ocean,” Isro said.
It added that controlled re-entries involve de-orbiting to very low altitudes to ensure impact occurs within a targeted safe zone and that 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.
Innovative workarounds were implemented by the operations team based on the study, deliberations, and exchanges among the mission, operations, flight dynamics, aerodynamics, propulsion, controls, navigation, thermal, and other sub-system design teams across the ISRO centres, who worked in synergy to surmount these challenges.
Stating that 18 orbit manoeuvres were performed to progressively lower the orbit, Isro said: “In between the de-orbiting, aero-braking studies at different solar panel orientations were also carried out to gain better insights into the physical process of atmospheric drag affecting the orbital decay of the satellite.”
The final de-boost strategy has been 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 of the thrusters.