The Indian Space Research Organisation (ISRO) successfully deorbited and re-entered the decommissioned Megha Tropiques-1 (MT-1) satellite into the Earth’s atmosphere. Launched on October 12, 2011, and built for tropical weather and climate studies, the MT-1 was ISRO’s first major joint satellite project with the French space agency, CNES. The orbital lifetime of this nearly 1-tonne satellite, which operated at an altitude of 867 km, was said to be more than 100 years. However, the MT-1 mission did not design the satellite to deorbit after the end of its life. However, when the MT-1’s mission ended, the two space agencies realized that some additional 120 kgs of fuel remained unused in the satellite’s fuel tank. ISRO used this opportunity intelligently and planned for a controlled re-entry to avoid it becoming a significant source of space debris.
Every satellite launched into space becomes space debris after some years, particularly at the end of its functional lifetime. Over time, such non-operational satellites continuously end up as space debris, which is much more hazardous to other functioning satellites. Space debris could be both natural and anthropogenic. Asteroids, comets, and meteoroids usually create natural space debris. Defunct satellites, objects released from the space station and astronaut space walks, the last stage of various rocket systems that deliver satellites into space, and their fragments often form anthropogenic space debris. The Chinese anti-satellite (ASAT) of 2007 and the Russian ASAT test of 2021 have been called for significantly contributing to space debris. The tests conducted by the US (2008) and India (2019) were at much lower altitudes, close to the Earth’s atmosphere. The debris created by these tests entered the Earth’s atmosphere and burnt off owing to the high re-entry temperatures of more than 2000 degrees Celsius.
Besides the ASAT fragments, over the years, the population of objects and defunct satellites in low Earth orbit (LEO) has increased significantly. These numbers have increased almost exponentially since various small-satellite constellations for providing space-based internet services, each consisting of thousands of satellites, are being launched. There is a palpable danger that the densely populated satellites in LEO could collide with each other and create more debris—a phenomenon known as the Kessler syndrome, which NASA scientist Donald J. Kessler first anticipated in 1978.
There is a requirement for a multi-pronged effort to limit the addition of more debris. It could be policy-based efforts, such as the debris mitigation guidelines of the United Nations and the Inter-Agency Space Debris Coordination Committee (IADC) or innovating technical measures to remove the existing debris and ensure that no additional debris gets added. But, besides these long shots, small and incremental steps could play a tremendous role if space agencies and private entities proactively take steps to avoid generating space debris. India took one small but crucial step in this direction on March 7.
Since MT-1 was not designed for controlled re-entry after the end of its life, ISRO proactively took upon itself complicated deorbiting operations, not part of MT-1’s mission design. An uninhabited area in the Pacific Ocean between 5°S to 14°S latitude and 119°W to 100°W longitude was identified as the targeted re-entry zone. As revealed by ISRO, since Aug 2022, the satellite’s perigee (the point in the orbit of a satellite at which it is nearest to the Earth) was progressively lowered using the available fuel through a series of 20 manoeuvres spread over eight months. It executed the final two de-boost burns on March 7 by firing four 11 Newton thrusters on board the satellite for about 20 minutes each. The last perigee was estimated to be less than 80 km, indicating that the satellite was possibly in one (or big) piece till that altitude and must have undergone structural disintegration. ISRO undertook a re-entry aero-thermal flux analysis and found no possibility of surviving large debris fragments. The subsequent telemetry data indicated the satellite’s complete breakdown in the remotest interiors of the vast Pacific Ocean. The meticulous operation happened as planned and was conducted from the Mission Operations Complex in ISTRAC.
More than a decade ago, the launch of the MT-1 satellite opened a new chapter in India’s atmospheric research capabilities. The observations from this satellite have played a crucial role towards providing continuous and reliable weather observations for the prognosis of various weather patterns. MT-1 provided critical atmospheric data on the equatorial region globally, which has been less studied earlier. MT-1 provided various observations about solar radiation, humidity and temperature profiles, water vapour profiles, cloud features, precipitation patterns, atmospheric motions, etc.
MT-1 was not a solitary pursuit but was part of an internationally collaborative satellite constellation. The MT-1, the US-Japan-led Global Precipitation Measurement (GPM) Core Observatory, among seven other satellites together form the Global Precipitation Measurement Constellation. There’s exciting trivia for those interested in popular culture references. GPM and Tropical Rainfall Measurement Mission (TRMM), another satellite of this constellation, found an interesting mention in the 2004 Bollywood movie Swades. The protagonist in Swades, Mohan Bhargav, played by Shahrukh Khan, was shown as a Project Manager of NASA’s GPM mission.
Performing controlled re-entry is exceptionally challenging, and ISRO deserves our congratulations for the MT-1 deorbit success. When any satellite becomes unusable (and becomes debris), it usually loses its pre-programmed orbit. Subsequently, complex and changing interactions between the atmosphere and debris occur. The longer such debris stays in the atmosphere, the more difficult it is to predict accurately the fallout area on-ground. There was a tremendous amount of planning that took place for the conduct of this operation. ISRO ensured that MT-1’s debris entered the atmosphere with a steep angle, and propulsion systems generated powerful thrust. It clinched uninterrupted visibility of the satellite debris and its complete disintegration from ground stations. ISRO had to ensure that no damage would happen to various operational satellites during its manoeuvres. It was extremely cautious about fully safeguarding any impact or debris moving close to the International Space Station and China’s Space Station, mainly because astronauts have been inhabiting these stations.
The menace of space debris has been recognized across space agencies for decades. However, it is only now that the earlier projected problems have begun to appear real due to the rapid growth in the number of orbital satellites. For a long time, NASA had guidelines indicating that satellites in LEO (below 2000 km altitude) must deorbit within a maximum of 25 years after completing their mission. However, realizing that the current threat was reaching a severe category on September 29, 2022, the US Federal Communications Commission adopted a new rule to reduce this requirement to five years for US-licensed satellites and those from other countries that seek to access the US market.
In future, the Indian government would be required to ensure that all satellites launched by its space agencies and the private sector would have provisions to undertake controlled re-entry. Typically, for all these years, many space players avoided such conditions owing to issues related to the mass and dimensions of the satellite and the over-and-above cost factors. But avoiding henceforth will become detrimental on a vast scale, even leading to a real Kessler Syndrome, this time not as a hypothesis, but for real.
At the policy level, on June 15, 2007, the UN Committee on the Peaceful Uses of Outer Space (PAROS) adopted space debris mitigation guidelines, and India fully supported it. Presently, various types of space debris removal technologies are under work. However, many of them are dual-use in nature and have strategic connotations. Addressing the challenge of this dual-use connotation demands establishing a rule-based, globally accepted mechanism to conduct various activities in space on multiple issues: from space debris removal to space traffic management and in-orbit servicing of satellites. With no particular technology operational, nor a consensus on using them, the world has a long way ahead. Today, India’s space programme is one of the most respected space programmes in the world due to its scientific expertise, cost efficiency, and overall transparency. Now the time has come for India to take the lead in undertaking policy initiatives in the space domain towards establishing a rule-based mechanism. The deorbiting of MT-1 is a laudable step in that direction; India has walked the talk regarding space debris mitigation and avoidance.
(The author is a Consultant, MP-IDSA, New Delhi. Views expressed are personal)
