About satellites
The low Earth satellite, Megha-Tropiques-1 (MT1), 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.
Although the satellite’s mission life was originally three years, the satellite has continued to provide valuable data services for over a decade, supporting regional and global climate models until 2021.
Why is it being deorbited?
The Inter-Agency Space Debris Coordination Committee’s guidance on space debris mitigation recommends deorbiting a low Earth orbit object at its end of life (EOL), preferably by controlled re-entry into a safe impact zone, or bringing it into orbit. Where the orbital lifetime is less than 25 years.
The orbital lifetime of MT1, weighing about 1,000 kilograms, can exceed 100 years in an operational orbit inclined at 20 degrees at an altitude of 867 kilometers. About 125 kg of on-board fuel remains unused at the end of its mission which could pose a risk of accidental break-up.
This residual fuel was estimated to be sufficient to achieve a fully controlled atmospheric reentry.
Why is it a challenge?
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 EOL.
“MT1 is not designed for EOL operation through controlled re-entry which makes the whole exercise very 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 the operational complexity.
MT1’s re-entry test has been undertaken as part of the ongoing effort as this satellite with sufficient residual fuel presents a unique opportunity to test relevant procedures and understand operational nuances related to post mission disposal via direct re-entry to Earth. atmosphere, ISRO said.
What could go wrong?
Controlled re-entry of a satellite is a complex and risky process, especially when the satellite is not designed for the process.
Some of the potential risks associated with controlled re-entry of a satellite include:
- Uncontrolled Trajectory: During the re-entry process, the satellite must follow a specific trajectory so that it lands in a specific area. However, if there is a fault or error in the guidance system, the satellite may deviate from its intended trajectory, potentially endangering populated areas.
- Structural damage: The intense heat generated during re-entry can weaken or break the satellite’s structure, increasing the risk of debris falling to the ground.
- Toxic materials: Some satellites may contain hazardous materials, such as radioactive isotopes or toxic chemicals. If these materials are not properly contained upon re-entry, they can pose a significant health risk to humans and the environment.
- Electrical malfunctions: The extreme heat and electromagnetic radiation generated during re-entry can cause electrical malfunctions in the satellite’s systems, resulting in loss of control or communications.
- Communication failure: During the re-entry process, it is essential for the ground control team to maintain communication with the satellite to ensure that it is following the correct trajectory. However, if there is a communication failure, it may be difficult or impossible to control the landing of the satellite.
- Weather conditions: Weather conditions such as strong winds, storms or turbulence can affect the satellite’s trajectory and increase the risk of it deviating from its intended path.
Where is the impact zone?
An uninhabited area between 5°S to 14°S latitude and 119°W to 100°W longitude in the Pacific Ocean was identified as the target re-entry zone for MT1.
Over 7 months of planning, coordination
Since August 2022, 18 orbit maneuvers have been performed to gradually lower the satellite’s orbit.
Between de-orbiting, aero-breaking studies were also conducted at different solar panel orientations to gain better insight into the physical mechanisms of atmospheric drag affecting satellite orbital decay.
When will ground impact occur?
The final de-boost strategy is designed considering a number of constraints, including visibility of the re-entry trace at the ground station, ground effects within the target area, and allowable operating conditions of the subsystems, particularly maximum deliverable thrust and maximum thrust. Firing duration of thrusters.
The final two D-boosts are expected to burn after ground impact between 16.30 hours and 19.30 hours on March 7.
Simulations show that no large chunks of the satellite are likely to survive aerothermal heating during re-entry.
(with input from agencies)
