How the moon kicked Chandrayaan-3 propulsion module into a new orbit

On December 30, astronomer Jonathan McDowell posted on

Dr. McDowell is known for, among other things, publishing Jonathan’s Space Report, “an irregular newsletter that attempts to provide a detailed and pedantic historical record of the space age” and for maintaining the ‘General Catalog of Artificial Space Objects’.

tug of war game

His post describes a common problem in spaceflight: When you leave a spacecraft coming anywhere near the path of the moon in a very large and unstable orbit around the earth, the moon’s gravity can keep nudging it in ways that are hard to predict in advance.

The “transition from lunar orbit” in his post means that the orbit of the object around the Earth reaches distances comparable to the distance of the Moon. As a result, at some points the object and the moon may pass relatively close to each other. When this happens, the moon’s gravity becomes very important.

In low earth orbit, that is, at an altitude of 150-2,000 km above sea level, gravity dominates and the movement of satellites there is quite regular. But as you approach the moon, you are effectively in a three-body situation: the Earth pulls, the moon pulls, and an object in between that is affected by both pulls moves rapidly in regions where the balance of these pulls changes.

In these systems, small differences in timing or location can lead to large differences later. Dr. This is what McDowell means by “chaotic.” The orbit is still subject to the laws of physics, but the underlying equations are very difficult to solve.

This was also the premise of the science fiction book and later the Netflix show ‘The 3 Body Problem’. An alien species lived on a world in a system where three suns orbited each other, constantly causing climate chaos. The three-body problem asks how three masses move when each pulls the other by gravity. There is no general closed form solution to this problem in classical mechanics; This means that there is no single formula by which you can predict how the system will evolve for all possible initial positions, velocities, and masses.

a circular path

The Chandrayaan-2 mission ended in partial failure when the lunar lander crashed into the lunar surface in 2019. But since it successfully launched an orbital module that continued orbiting the moon, the Chandrayaan-3 mission consisted of only a propulsion module, a lander and a rover.

After the lander and rover landed on the moon in August 2023, the Indian Space Research Organization (ISRO) moved the propulsion module into a 125,000 x 305,000 km orbit around the earth in October. These two numbers are the distances to the earth at the closest point (perigee) and farthest point (apogee) of the orbit.

So the thruster module orbited the earth in a highly elliptical path: it approached to about 125,000 km, then increased to about 305,000 km, approaching the average distance of the moon (~384,000 km). This means it spends some of its time in the moon’s gravitational zone.

kick of the moon

Dr. When McDowell says he “tackled the Moon in November,” he means the thruster module made a relatively close pass by the Moon. During a close flyby, the moon’s gravity can kick or suddenly change the object’s speed and orientation relative to the Earth. This is not like friction or collision, it is a purely gravitational interaction. Depending on the geometry, the kick can raise, lower, tilt, or change the shape of the orbit.

According to a ISRO notification In November, the propulsion module entered the Moon’s “domain” on November 4 and exited it on November 14. The organization said it was tracking the “event” using the Indian Deep Space Network (IDSN), a collection of antennas near Bengaluru that tracks India’s assets in space, along with data from similar ground stations operated by NASA and other space agencies.

While within the lunar radius, the propulsion module passed by the moon twice: on November 6, it came within 3,740 km of the lunar surface, and on November 11, it came within 4,537 km.

Following this encounter, the thrust module’s orbit changed in three ways. First, it has become much larger overall. According to ISRO, the peak jumped to 727,000 km; Dr. McDowell wrote in his post on December 30 that its altitude is 983,000 km. Both numbers are far beyond the distance of the Moon and are a sign that the Moon’s gravity is adding (or rearranging) orbital energy to the Earth’s frame.

Second, the new orbit has a different shape and orientation. ISRO estimates that the perigee point is 409,000 km and Dr. McDowell concluded it had 365,000 km. So, the propulsion module no longer returns anywhere near 125,000 km; it almost always remains high. Third, the orbit was noticeably tilted 22 degrees relative to the Earth’s equator. This was because the moon’s gravity was pulling the module in a direction that was not perfectly aligned with its current motion and orbital plane. As a result, the angular momentum vector of the module changed.

Very different orbit

According to the statement, ISRO “took special care to monitor its orbit and proximity to other space objects.” “Overall satellite performance was normal during the flight, and no encounters with other lunar orbiters occurred. This event yielded valuable information and experience from the perspectives of mission planning, operations, flight dynamics, and in particular improved the understanding of disturbance torque effects.”

In a nutshell, ISRO has left the Chandrayaan-3 thrust module in a wide earth orbit that grazes the periphery of the moon. In November 2025, the timing is set so that the moon will be close enough to strongly pull the propulsion module. This reshaped its orbit, pushing it into a higher, more inclined, and more extreme ellipse. As a result, tracking teams now found it with very different orbital parameters.

Dr. In his post, McDowell thanked amateur astronomer Sam Deen, astronomer Luca Buzzi, and Bill Gray, who developed remarkable software for tracking near-Earth objects, “for finding that the suspected asteroid CE1M9G2 was actually Chandrayaan-3.”

It was published – 30 December 2025 08:37 IST