Indian Space Research Organisation launched a satellite in a controlled manner For the first time since the end of life, earlier this week. The weather satellite Megha Tropics-1, which was built as a joint mission by the Indian and French space agencies, entered the atmosphere on Tuesday after the final two maneuvers and burned up over the Pacific Ocean.
How was the satellite brought down?
The Megha Tropics satellite was launched on a ship PSLV by the Space Agency in 2011. And, although the satellite’s planned mission life was only three years, it has been providing information on the water cycle and energy exchange in the tropics for nearly a decade.
With more than 120 kg of fuel left on the satellite after separation, the space agency determined that was enough to attempt a controlled re-entry, in which a series of 20 maneuvers over eight months lowered the satellite’s orbit enough that it would re-enter. On Tuesday, it entered the dense atmosphere and burned.
This was the first time that the space agency had tried such a technique to clean up space debris, even though the satellite had not been built. “Re-entry wasn’t really planned as part of the mission; There was fuel left so ISRO tried. Normally, satellites are left in their orbits and fall into the atmosphere over years due to Earth’s gravitational pull. When satellites re-enter the atmosphere, friction heats it up to extremely high temperatures of thousands of degrees Celsius. Without a heat shield, a controlled re-entry or uncontrolled burns up 99% of a satellite,” said Ajay Lele, senior fellow at the Manohar Parrikar Institute for Defense Studies and Analysis.
Why did ISRO attempt controlled re-entry?
With no extra fuel conveniently left on the satellite after the end of its mission life, ISRO attempted to re-enter the controls to demonstrate and understand the process of doing so.
With several space fair countries and private companies launching satellites, mostly in low Earth orbit, keeping space clean has become imperative. Thousands of objects are flying in this orbit; Not just the old satellites and their parts but the final stages of the rockets that got them there. moving at extremely high speeds, Even the smallest debris can destroy an active satellite.
Scarier still is Kessler syndrome – a scenario in which the extent of space destruction reaches a point where they trigger others with just one collision.
This is the reason Space ruins Satellites are monitored and sometimes have to be moved out of their path. According to Minister of State for Space Dr Jitendra Singh’s reply in Parliament, ISRO runs 21 such collision courses in 2022. In fact, the space agency last year set up a department to monitor space debris and mitigate the risks posed.
The space agency was also following UN guidelines Inter-Agency Space Debris Coordinating Committee (IADC) who say that satellites should be deorbited after mission life – either by controlled entry into a safe impact zone as ISRO attempted with Megh Tropics-1, or by deorbiting (the time it takes) a satellite to reduce the orbital lifetime. to drop from a fixed orbit on its own) in less than 25 years.
It is also recommended that in such cases the stored fuel is removed from the spacecraft to avoid an accident that breaks up the satellite in space and creates more debris. In the case of Megha Tropics-1, an 867 km orbit with a 20 degree inclination means an orbital lifetime of over 100 years. And, the spacecraft had more than 120 kg of fuel left.
What are satellites usually?
A controlled re-entry has been attempted ISRO Only possible for satellites in low-Earth orbit – about 1,000 kilometers above Earth’s surface – is the launch of this week. These techniques, however, are not usually attempted because of the need to conserve fuel on the satellite after the end of the mission life.
And, this is impossible for satellites placed in geo-stationary or geosynchronous orbit – where the satellite’s time to orbit the Earth matches the Earth’s rotation – because they are at an altitude of about 36,000 km. “To bring down a satellite like that in orbit would require a huge fuel reserve. This will only make the satellite heavier and more expensive during launch,” Lele said.
Considering that it takes 20 to 30 years to fall into the atmosphere naturally from low Earth orbit, it will take generations to read those in geosynchronous or geo-stationary orbit, an ISRO official said.
So, what happens to these higher orbit satellites? “They usually migrate in what is known as the graveyard orbit. Instead of shooting them down, they are shot upwards at the end of life,” Lele said. The ISRO official added, “These orbits are like parking lots in space where all the old satellites are kept. Sometimes a satellite can escape into deep space as well.” A satellite escapes into deep space when its speed increases enough to move away from Earth’s gravitational pull.
Has ISRO satellite debris showered in the past?
Actually it doesn’t. “About 99.9 percent of a satellite burns up in the atmosphere. We haven’t really seen an instance of debris raining over populated areas,” the ISRO official said. Satellites in low Earth orbit are usually smaller and therefore more likely to disintegrate on entry into the atmosphere.
Also, the ISRO official said, the space agency usually uses aluminum and composites to make satellites. These materials have a low flash point and are easily destroyed in the atmosphere.
