Chandrayaan 3 and Luna 25 are joining six other spacecraft in lunar orbit, as they prepare to land near the Moon’s south pole. Lunar orbit is getting crowded and risky, requiring close coordination and collision avoidance manoeuvres among the space agencies. Lunar exploration is expected to increase in the future, with scientific, commercial, and crewed missions, calling for new guidelines and best practices for space operations.
When Chandrayaan 3 injected itself into lunar orbit on August 6, 2023, there were six spacecraft already in orbit around the Moon. Four of these are NASA missions, the Lunar Reconnaissance Orbiter (LRO), Capstone, and a pair of Artemis probes. ISRO’s own Chandrayaan 2 continues to orbit the Moon, collecting valuable data along with the Korea Pathfinder Lunar Orbiter, also known as Danuri.
Additionally, there are two defunct spacecraft in orbit, the Chandrayaan 1 mission and the JAXA’s Ouna spacecraft. All the other spacecraft that have ever entered lunar orbit have either crashed into the surface of the Moon, or moved to an orbit that is not bound to the Moon, such as the Chinese relay satellite Queqiao for the Chang’e 4 mission that has been moved to a halo orbit around the second Moon-Earth Lagrange point.
The Russian Luna 25 mission which is about to be launched in a few hours, will reach lunar orbit by August 16, and will be attempting to land north of the Boguslavsky crater between August 21 and 24, 2023. Chandrayaan 3 will be joining it at the earliest on August 23, at a distance of about 100 kilometres, close to the Manzinus crater.
Lunar orbit is getting crowded, and is only expected to get even more crowded in the future. The LRO, Danuri and Chandrayaan 2 mission all have overlapping orbital regimes and frequently have to move out of each other’s way in anticipated conjunctions, in what are known as collision avoidance manoeuvres (CAMs). Chandrayaan 2 has so far conducted three CAMs to avoid a potential crash into LRO or Danuri. All the space agencies are working closely together to avoid a crash in lunar orbit.
For the Chandrayaan 3 mission, each of the lunar bound manoeuvres that take the spacecraft closer to the lunar surface are being carried out after assessing potential risk and close approaches with other lunar orbiters. There is less orbital knowledge of the lunar regime, compared to say low-Earth orbit, which increases the chances of a collision. ISRO is working with international agencies such as the Inter Agency Space Debris Coordination Committee (IADC) to formulate best practices and guidelines for operations in lunar orbit.
So far, most of the missions to the Moon had scientific goals or were technology demonstrations. In the future, there are expected to be private as well as commercial missions to the lunar surface. The number of orbiters, landers and rovers operating on the lunar surface is expected to grow. NASA has the ambitious Artemis 3 programme, while China and Russia are collaborating on an International Research Station, that will eventually support visits by crew.
The current international guidelines for space debris mitigation are focused on low Earth orbit. Space agencies will take the lessons learned from operating in Earth orbit, and apply them to the lunar orbit. ISRO committed to the safe and sustainable exploration of outer space, and follows all the international guidelines for space operations.