The ISRO and its international collaborators strive to dispose of their satellites rather than let them hang around, thus preventing bad hygiene of the cosmos as well as astronomical accidents read more

The skies are getting filled with worthlessly orbiting garbage. That would be a layman’s lingo, describing space debris. Many satellites that retired and were abandoned once their shelf lives were over never returned or crashed back on the earth’s surface. A crash happens when a space mission is unsuccessful. This is about successful missions whose logical conclusion man should have spared a thought to right at the inception of rocket science but didn’t. Nature, which does not house this planet alone, encompasses the universe and, therefore, conservation measures must include ensuring the sanitation of the vast emptiness that abounds out there. We have no business reducing it to a dump yard of decommissioned machines.

In 2023, the global community contributed 3,143 entities to the enormous expanse of space, marking a significant increase of 24% in space junk over the preceding year’s count of 2,533. Our own Indian Space Research Organisation (ISRO) took proactive measures by executing 25 collision-avoidance manoeuvres (CAM) within the same year. The ISRO disclosed these noteworthy statistics through a comprehensive report during the final week of March, shedding light on its meticulous management of satellites and space assets amidst the escalating concern of space debris.

And a clean-up exercise would make sense even to the selfish humanity. These ‘flying dustbins’, besides making space dirty, pose an imminent danger to the ever-new man-made satellites launched by rockets, for which scientists need to work out new elliptical routes of revolutions aka orbits — whether they are geosynchronous (earth-centred) or geostationary (constantly looking at one ‘face’ of the earth). This navigational concern is over and above that of steering clear of asteroids, comets, meteoroids, energy and particle flux and artificial objects in the new artificial satellite’s course.

Such CAM is like the survivors in a zombie apocalypse movie negotiating their way through abandoned objects where haphazard platoons of the ‘walking dead’ may threaten their progress now and then. This is no child’s play, as staying alert to incoming spatial threats involves a complex exercise of difficult calculations. Approximately 1,37,565 close approach alerts were received from USSPACECOM, which were then reassessed using precise orbital data of Indian operational satellites. Of these, 3,033 alerts were pinpointed for close approaches within 1 km of ISRO satellites. Additionally, about 2,700 close approaches were monitored with other operational satellites within a 5 km radius. Collaboration with international agencies such as SpaceX and EUMETSAT, was undertaken on specific occasions. Nevertheless, none of the close approaches were judged to be critical and did not warrant a CAM.

As a responsible nation in the elite league of countries with advanced astronomical know-how, India now plans to have only such missions in the future, beginning in 2030, where its satellites wouldn’t turn into useless bodies rotating and revolving around a star, planet or natural satellite once they retire. This is the plan ISRO’s chairman S Somanath shared with the Inter-Agency Debris Coordination Committee (IADC) during its meeting in Bangalore on 16 April 16.

We have already initiated this process by ensuring the safe return of fully utilised satellites to the earth’s atmosphere. By the end of 2023, according to the ISRO report, 21 Indian satellites had re-entered the atmosphere. In 2023 alone, eight Indian satellites underwent controlled re-entry, including Megha-tropiques-1 that faced a highly challenging exercise.

Furthermore, until 2023, a total of 82 rocket bodies from Indian launches were placed in various orbits. Unfortunately, the upper stage of PSLV-C3 experienced an accidental break-up in 2001, resulting in the creation of 371 debris fragments. Although the majority of these fragments have re-entered the atmosphere, 52 pieces of PSLV-C3 debris remained in orbit until the end of 2023.

Among the remaining intact Indian upper stages, 35 rocket bodies successfully re-entered the earth’s atmosphere by the end of the year. In 2023, there were five other re-entries of this nature.

In terms of ISRO’s launches in 2023, all seven missions — namely SSLV-D2/EOS7, LVM3-M3/ONEWEB_II, PSLV-C55/TeLEOS-2, GSLV-F12 NVS-01, LVM3-M4/Chandrayaan-3, PSLV-C56/DS-SAR and PSLV-C57/Aditya L-1 — were successful. These launches resulted in the placement of five Indian satellites, 46 foreign satellites and eight rocket bodies (including POEM-2) into their designated orbits, the report says.

Ensuring that our satellites do not clutter space post-‘superannuation’ is no mean feat. Three examples should suffice to explain the delicate situations. First, the scheduled launch of PSLV-C55/Te-LEOS-2 had to be postponed by 60 s after conducting a COLA analysis. This was necessary to prevent potential collisions between an operational satellite and the injected satellites during their orbital phase, as their operational altitudes overlapped. Second, in the case of LVM3-M4/ Chandrayaan-3, the planned lift-off had to be delayed by 4 s following a COLA analysis. This precautionary measure was taken to avoid any close encounters between a debris object and the injected satellites during their orbital phase, as their operational altitudes overlapped. Third, the nominal lift-off of PSLV-C56/ DS-SAR had to be postponed by 1 min after a thorough COLA analysis. This decision was made to prevent potential close approaches between Starlink satellites and the injected satellites during their orbital phase, as their operational altitudes overlapped.

Finally, here is how the ISRO is taking care of decommissioning and post-mission disposal of whatever it sends up there. In 2023, one of the significant events was the controlled re-entry of Meghatropiques-1 into the earth’s atmosphere above an uninhabited region in the South Pacific Ocean. The spacecraft underwent 20 perigee-lowering manoeuvres to de-orbit, using approximately 120 kg of fuel. The final de-boost and re-entry occurred on March 7, 2023, and was monitored by the ISRO ground station.

Following the injection of payloads, the upper stage of PSLV-C56 was de-orbited to a nearly circular orbit at 300 km. Within a month, the rocket body re-entered the atmosphere due to drag forces.

GSAT-12 was officially decommissioned on March 23, 2023, after being raised to a super-synchronous orbit by approximately 400 km. The disposal orbit adhered perfectly to the IADC-recommended guidelines.

The decommissioning of IRS-P6 has been approved, with final passivation scheduled for early 2024. Plans have been finalised for the passivation of another decommissioned satellite, Cartosat-2, set for atmospheric re-entry by February 2024.

The propulsion module of Chandrayaan-3 was re-orbited into a lunar escape trajectory and positioned in a high earth orbit with an altitude exceeding 2 million km.

Oceansat-2 was placed in an orbit at 900 km altitude with a relatively low population due to the constraints of the ageing spacecraft preventing de-orbiting.

Of course, the world is helping. India, as a signatory to all major space treaties, has consistently stressed the importance of long-term sustainability in outer space endeavours. The ISRO System for Safe and Sustainable Operations Management (IS4OM) has been in operation since 2022 to protect the Indian agency’s space assets and enhance adherence to globally recognised standards for the long-term sustainability of activities in outer space.

The ISRO actively engages in various international platforms, including the Inter-Agency Debris Coordination Committee (IADC) comprising 13 space agencies, the International Academy of Astronautics (IAA) space debris working group, the International Astronautical Federation (IAF) space traffic management working group, the International Organisation for Standardisation (ISO) space debris working group, and the UN-COPUOS scientific and technical sub-committee/legal sub-committee. These forums facilitate discussions on space debris issues, relevant research and the long-term sustainability of outer space activities. India currently chairs the UN working group on the Long-term Sustainability of Outer Space Activities and will host the 42nd annual IADC meeting in April 2024 during its tenure as the IADC chair for 2023-24.

In addition, the ISRO actively participated in the IADC’s annual re-entry campaign in 2023, using ERS-02 as the test object and sharing re-entry forecasts. The ISRO delegation has made significant contributions to revising IADC space debris mitigation guidelines, evaluating the impact of large constellations on space operations, expanding debris mitigation guidelines to the cis-lunar region, and addressing other aspects of space sustainability within the IADC framework.

(With Agency Inputs)