Isro brings down decommissioned weather satellite : What is a controlled re-entry? Why is it done?

Isro brings down decommissioned weather satellite : What is a controlled re-entry? Why is it done?

Context- The Indian Space Research Organisation brought down a satellite in a controlled manner after its end of life, for the first time earlier this week. The weather satellite Megha Tropiques-1, which was developed as a joint mission by Indian and French space agencies, entered the atmosphere after the final two maneuvers on Tuesday and burnt up over the Pacific Ocean.

(Credits- Indian Express)

How was the satellite brought down?

  • The Megha Tropiques satellite was launched aboard a PSLV by the space agency in 2011. And, although the planned mission life of the satellite was only three years, it continued providing data on water cycle and energy exchanges in the tropics for nearly a decade.
  • With over 120 kgs of fuel remaining in the satellite even after being decommissioned, the space agency determined that there was enough to attempt a controlled re-entry, where a series of 20 manoeuvres over eight months lowered the orbit of the satellite such that it re-entered the dense atmosphere on Tuesday and burned up.
  • The re-entry was not really planned as part of the mission; there was fuel left so Isro attempted it. Usually, satellites are left in their orbit and because of the gravitational pull of the earth, they come down to the atmosphere over years and years.
  • 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.

Why did Isro attempt a controlled re-entry?

  • Other than extra fuel conveniently 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 space fairing nations and private entities launching satellites, mostly in low earth orbits, it has become imperative to keep the space clean.
  • There are thousands of objects flying around in these orbits; not just old satellites and their parts but also last stages of the rockets that take them there. Moving at extremely high speeds, even the smallest debris can destroy active satellites.
  • Scarier still is Kessler syndrome – a scenario where the amount of space debris reaches a point where they just create more with one collision triggering others.

What happens to satellites usually?

  • A controlled re-entry like the one attempted by Isro earlier this week is possible only for satellites in the 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.
  • And, 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 as orbit, a huge fuel reserve would be needed. This will only make the satellite heavier and costlier at launch”.

Source- Indian Express

NEWS- Isro brings down decommissioned weather satellite : What is a controlled re-entry? Why is it done?

Syllabus- Prelims; Current Affairs