BENGALAURU: Isro is preparing for a challenging experiment in the controlled re-entry of a decommissioned low-Earth orbit satellite – Megha-Tropiques-1 (MT1) – on 7 March. MT1 was launched on October 12, 2011, as a joint satellite venture of Isro and the French space agency, CNES, for climate and tropical climate studies.
According to the space agency, an uninhabited area in the Pacific Ocean between 5°S and 14°S latitude and between 119°W and 100°W longitude has been identified as a targeted reentry zone for MT1. And, since August 2022, 18 orbital maneuvers have been performed to progressively lower the orbit of the satellite.
The last two de-boost burns followed by the ground impact are expected to occur between 4:30 and 7:30 pm on March 7, and ISRO said aerothermal simulations showed large fragments from the satellites were not likely to survive the aerothermal heating during reentry.
“Although the mission life was originally up to three years, the satellite has continued to provide valuable data services for more than a decade while supporting regional and global climate models through 2021,” Isro said.
The United Nations Inter-Agency Space Debris Coordinating Committee (IADC) Space Debris Mitigation Guidelines recommend deorbiting an object in low Earth orbit (LEO) at the end of its life cycle, preferably through re-entry controlled in a safe impact zone, or by bringing it into an orbit where the orbital life is less than 25 years. It is also recommended to carry out the “passivation” of the on-board energy sources to minimize the risk of accidental post-mission breakage.
“The orbital life of MT1, weighing approximately 1,000 kg, would have been over 100 years in its 20 degree inclined operational orbit at 867 km altitude. Approximately 125 kg of fuel on board remained unused at the end of the mission, which could pose risks of accidental breakage. This residual fuel is estimated to be sufficient to achieve a fully controlled atmospheric reentry to strike an uninhabited location in the Pacific Ocean,” Isro said.
He added that controlled reentries involve deorbiting at very low altitudes to ensure impact occurs within a targeted safe zone, and that usually large satellites/rocket bodies that can survive aerothermal fragmentation upon reentry are subjected to controlled return to limit the risk of accidents on the ground.
“However, all of these satellites are specifically designed to undergo controlled re-entry at the end of their life cycle. MT1 was not designed for EOL extension operations through controlled re-entry which made the entire exercise extremely challenging. Additionally, constraints aboard the older satellite, where several systems had lost redundancy and exhibited degraded performance, and maintaining subsystems under harsher environmental conditions at an orbital altitude much lower than originally designed, added to the complexities operations,” Isro said.
Innovative workarounds were implemented by the operations team based on the study, deliberations and exchanges between the mission, operations, flight dynamics, aerodynamics, propulsion, controls, navigation, thermal and other teams of subsystem design in ISRO centres, which have worked in synergy to overcome these challenges.
Stating that 18 orbital maneuvers were performed to progressively lower the orbit, ISRO said, “Among deorbiting and air braking studies with different solar array orientations were also performed to get a better understanding of the physical process of atmospheric drag that affects the satellite’s orbital decay.
The final de-boost strategy was designed after taking into consideration several constraints, including the visibility of the reentry track on the ground stations, the impact with the ground within the target zone and the allowed operating conditions of the subsystems , in particular the maximum thrust that can be delivered and the maximum duration of the fire of the thrusters.
According to the space agency, an uninhabited area in the Pacific Ocean between 5°S and 14°S latitude and between 119°W and 100°W longitude has been identified as a targeted reentry zone for MT1. And, since August 2022, 18 orbital maneuvers have been performed to progressively lower the orbit of the satellite.
The last two de-boost burns followed by the ground impact are expected to occur between 4:30 and 7:30 pm on March 7, and ISRO said aerothermal simulations showed large fragments from the satellites were not likely to survive the aerothermal heating during reentry.
“Although the mission life was originally up to three years, the satellite has continued to provide valuable data services for more than a decade while supporting regional and global climate models through 2021,” Isro said.
The United Nations Inter-Agency Space Debris Coordinating Committee (IADC) Space Debris Mitigation Guidelines recommend deorbiting an object in low Earth orbit (LEO) at the end of its life cycle, preferably through re-entry controlled in a safe impact zone, or by bringing it into an orbit where the orbital life is less than 25 years. It is also recommended to carry out the “passivation” of the on-board energy sources to minimize the risk of accidental post-mission breakage.
“The orbital life of MT1, weighing approximately 1,000 kg, would have been over 100 years in its 20 degree inclined operational orbit at 867 km altitude. Approximately 125 kg of fuel on board remained unused at the end of the mission, which could pose risks of accidental breakage. This residual fuel is estimated to be sufficient to achieve a fully controlled atmospheric reentry to strike an uninhabited location in the Pacific Ocean,” Isro said.
He added that controlled reentries involve deorbiting at very low altitudes to ensure impact occurs within a targeted safe zone, and that usually large satellites/rocket bodies that can survive aerothermal fragmentation upon reentry are subjected to controlled return to limit the risk of accidents on the ground.
“However, all of these satellites are specifically designed to undergo controlled re-entry at the end of their life cycle. MT1 was not designed for EOL extension operations through controlled re-entry which made the entire exercise extremely challenging. Additionally, constraints aboard the older satellite, where several systems had lost redundancy and exhibited degraded performance, and maintaining subsystems under harsher environmental conditions at an orbital altitude much lower than originally designed, added to the complexities operations,” Isro said.
Innovative workarounds were implemented by the operations team based on the study, deliberations and exchanges between the mission, operations, flight dynamics, aerodynamics, propulsion, controls, navigation, thermal and other teams of subsystem design in ISRO centres, which have worked in synergy to overcome these challenges.
Stating that 18 orbital maneuvers were performed to progressively lower the orbit, ISRO said, “Among deorbiting and air braking studies with different solar array orientations were also performed to get a better understanding of the physical process of atmospheric drag that affects the satellite’s orbital decay.
The final de-boost strategy was designed after taking into consideration several constraints, including the visibility of the reentry track on the ground stations, the impact with the ground within the target zone and the allowed operating conditions of the subsystems , in particular the maximum thrust that can be delivered and the maximum duration of the fire of the thrusters.
