Note4Students

From UPSC perspective, the following things are important :

Prelims level: Megha Tropiques Satellite, Controlled re-entry

Mains level: Space junk clearing

sat

ISRO attempted a controlled re-entry of the Megha Tropiques-1 satellite with leftover fuel to lower the orbit and reduce space debris.

Megha Tropiques Satellite

The weather satellite Megha Tropiques-1 was developed as a joint mission by Indian and French space agencies.
It 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.

How was the satellite brought down?

With over 120kgs of fuel remaining in the satellite even after being decommissioned.
ISRO determined that there was enough to attempt a controlled re-entry.
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.

This was the first time that ISRO attempted such a manoeuvre to clear out space debris despite the satellite not being built to do so.
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.

ISRO attempted the control re-entry to demonstrate and understand the process of doing so.
Keeping space clean is crucial with multiple spacefaring nations and private entities launching satellites.
Thousands of objects are flying around in low earth orbits, including old satellites, parts, and rocket stages.
Even small debris can destroy active satellites due to high speeds.
Kessler syndrome is a scary scenario where space debris collisions create more debris.

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.
Such satellites 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.