Highlights: 

• ISRO faces the significant challenge of managing the increasing traffic in lunar orbits. 
• Chandrayaan 2 Orbiter has already undergone three Collision Avoidance Manoeuvres (CAM) to prevent close approaches with other spacecraft.
• ISRO emphasises the importance of understanding the space environment and formulating mitigation practices to ensure the safety of spacecraft in lunar orbits. 

As the deadline approaches the country eagerly awaits the landing of Chandrayaan 3 Lander, Vikram, on the Lunar surface. The space agency, ISRO is currently grappling with the challenge of managing the increasing traffic in the vicinity of the Moon. Moon is currently witnessing a surge in space activity, transforming it into a bustling centre of lunar missions with six active lunar orbiters. Alongside India’s Chandrayaan-3, several other significant players are present.

This makes it crucial for ISRO to monitor the Chandrayaan 2 Orbiter, which entered lunar orbit in 2019. Chandrayaan 3 has already undergone three Collision Avoidance Manoeuvres (CAM) to prevent potential collisions with other spacecraft. Nasa’s Lunar Reconnaissance Orbiter (LRO), launched in June 2009, has been operating at 50-200 km altitude, supplying detailed maps of the lunar surface. The ARTEMIS P1 and P2 probes, which were initially part of the THEMIS mission but have been repurposed under ARTEMIS, have maintained stable equatorial orbits with high eccentricity at altitudes of approximately 100 km x 19,000 km since their insertion into lunar orbit in June 2011.

To ensure safety and prevent close approach threats in planetary orbits, ISRO underscores the need to comprehensively understand the environment and formulate effective mitigation practices. 

Currently, the UN and the Inter-Agency Space Debris Coordination Committee (DC) guidelines for space debris mitigation focus on objects injected into Earth’s orbit, leaving a gap in addressing the challenges posed by objects in lunar orbits.

ISRO acknowledges the complexities of tracking and observing deep space objects, emphasising the greater complexity compared to near-Earth observations due to the significant distance between the observer and the object, resulting in latency, signal attenuation, and associated complexities. The agency discussed various techniques such as range and Doppler measurement, Very Long Baseline Interferometry (VLBI)/Delta Differential One-Way Ranging (DOR), and Laser ranging with retro-reflectors for tracking functional assets like spacecraft, landers, and rovers.

ISRO mentioned that for safer landing it is important to delve into the intricacies of lunar orbits, the influence of lunar gravity, the gravity of the Sun and Earth, and solar radiation pressure on orbital evolution. It talked about the advantages of Near Rectilinear Halo Orbits (NRHO) in terms of stability and continuous communication, making them suitable for lunar gateways. Despite the expected increase in lunar missions, no congestion is foreseen in the vast spatial extent of NRHO orbits.

Currently, several active lunar orbiters, including Chandrayaan-2, operate in Low Lunar Orbit (LLO), which requires careful coordination and risk assessment to avoid close approaches and potential collisions. ISRO’s System for Safe and Sustainable Space Operations Management (IS4OM) conducts critical analyses of lunar-bound manoeuvres to assess the risks of close approaches with other lunar orbiters before executing these manoeuvres.

Given the growing space object population in the lunar environment, ISRO acknowledges the necessity of collision risk assessment for the safe operations of spacecraft orbiting the Moon. Collaborating with international organisations like the Inter-Agency Space Debris Coordination Committee (IADC), India is actively working on specific guidelines and best practices to ensure the sustainability of space operations in cislunar and lunar regions.

Read | Chandrayaan-3 Set for Launch Today, Anticipated Lunar Landing on August 23

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