Why in News?

• The Indian Space Research Organisation (ISRO) for the first time brought down a satellite - Megha Tropiques-1, in a controlled manner after its end of life.
• Although the mission life of the weather satellite - a joint India-France mission launched aboard a PSLV in 2011, was only 3 years, it continued providing data on water cycle, energy exchanges in the tropics for nearly a decade.

What’s in Today’s Article?

• What Happens to Satellites after their Life ends?
• How ISRO Brought Down the Satellite?
• Why did ISRO Attempt a Controlled Re-entry?

What Happens to Satellites after their Life ends?

• Usually, satellites are left in their orbit and because of the gravitational pull of the earth, they come down to the atmosphere over years.
• It takes debris from the low earth orbit 20 to 30 years to fall to the atmosphere and generations for those in geosynchronous or geo-stationary orbits to fall.
  • When the satellites re-enter the atmosphere, the friction causes it to heat up to extreme high temperatures of thousands of degrees Celsius.
  • Without a heat shield, 99% of a satellite gets burnt up whether in a controlled re-entry or an uncontrolled one.
• A controlled re-entry is possible only for satellites in low-earth orbit - at about 1,000 kms over the surface of the earth.
  • These manoeuvres, however, are not usually attempted because fuel reserves have to be maintained in the satellite after mission life is over.
• This is impossible for satellites placed in geo-stationary or geosynchronous orbit - where time taken by the satellite to orbit the earth matches Earth’s rotation - because they are at altitudes of nearly 36,000 kms.
  • For attempting to bring down a satellite from such an orbit, a huge fuel reserve would be needed, which will only make the satellite heavier and costlier at launch.
  • Therefore, instead of bringing them down, they are shot upwards at the end of life. These orbits are like parking lots in space where all old satellites are put in.
  • Sometimes a satellite might escape to deep space (when its velocity increases enough to get away from the gravitational pull of the earth) as well.

 How ISRO Brought Down the Satellite?

• This was the first time that the space agency attempted such a manoeuvre to clear out space debris despite the satellite not being built to do so.
• With over 120kgs of fuel remaining in the satellite even after being decommissioned, the space agency attempted a controlled re-entry.
• A series of 20 manoeuvres over eight months lowered the orbit of the satellite such that it re-entered the dense atmosphere and burnt up over the Pacific Ocean.

 Why did ISRO Attempt a Controlled Re-entry?

• Other than extra fuel remaining in the satellite after the mission life ended, ISRO attempted the control re-entry to demonstrate and understand the process of doing so.
• With several satellites/other objects/debris moving at extremely high speeds in low earth orbits, it has become imperative to keep the space clean as even the smallest debris can destroy active satellites.
  • Kessler syndrome - a scenario where the amount of space debris reaches a point where they just create more with one collision triggering others - is even scarier.
• This is the reason space debris is monitored and sometimes satellites have to be moved from their way.
• For example, ISRO carried out 21 such collision course manoeuvres in 2022 and set up a department last year to monitor the space debris and mitigate the risks posed.
• The space agency was also following the guidelines of UN and the Inter-Agency Space Debris Coordination Committee (IADC) that say satellites should be deorbited after mission life.
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