Context: 

ISRO is gearing up for a challenging experiment of controlled re-entry of a decommissioned low Earth orbiting satellite, namely Megha-Tropiques-1 (MT1).

About Megha-Tropiques-1 (MT1).

• MT1 was launched in 2011, as a joint satellite venture of ISRO and the French space agency CNES for tropical weather and climate studies. 
• Mission life: 3 years, the satellite continued to provide valuable data services for more than a decade supporting regional and global climate models till 2021.
  • The orbital lifetime of MT1, weighing about 1000 kg, would have been more than 100 years in its 20 deg inclined operational orbit of 867 km altitude. 
• About 125 kg 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.

Controlled Re-Entries:

• United Nations/Inter-Agency Space Debris Coordination Committee (UN/IADC) guidelines suggest that LEO objects should be deorbited at their end-of-life, either through controlled re-entry to a safe zone or by moving them to an orbit with a shorter lifetime of less than 25 years to mitigate space debris.
• It is also recommended to carry out “passivation” of on-board energy sources to minimise the risk of any post-mission accidental break-up.
• Controlled re-entries involve deorbiting to very low altitudes to ensure impact occurs within a targeted safe zone.
• 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. 
• However, all such satellites are specifically designed to undergo controlled re-entry at end-of-life. 

News Source: The Hindu