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

On December 30, astronomer Jonathan McDowell posted connected X.com: “The abandoned Chandrayaan-3 propulsion module, near successful a 125000 x 305000 km orbit successful 2024, had a spot of a tussle with the Moon successful November and has present been recovered successful a 365000 x 983000 km x 22 deg orbit”.

Dr. McDowell is well-known for, among different things, publishing Jonathan’s Space Report, “an irregular newsletter which attempts to supply a elaborate and pedantic humanities grounds of the abstraction age” and for maintaining the ‘General Catalog of Artificial Space Objects’.

Tug of war

His station describes a communal occupation successful spaceflight: erstwhile you permission a spacecraft successful a precise ample and lopsided orbit astir the world that comes anyplace adjacent the moon’s path, the moon’s gravity tin support nudging it successful ways that are hard to foretell acold successful advance.

“Moon-orbit-crossing” successful his station means the object’s orbit astir the world reaches retired to distances comparable to the moon’s distance. As a effect astatine immoderate points the entity and the satellite tin walk comparatively adjacent to each other. When that happens, the moon’s gravity matters a lot.

In low-earth orbit, i.e. 150-2,000 km supra oversea level, the earth’s gravity dominates and the question of satellites present is reasonably regular. But erstwhile you get person to the moon, you’re efficaciously successful a three-body situation: the world pulls, the satellite pulls, and an entity successful betwixt that’s affected by some their pulls moves rapidly done regions wherever the equilibrium of those pulls changes.

In these systems, tiny differences successful timing oregon presumption tin pb to large differences later. That is what Dr. McDowell meant by “chaotic”. The orbit is inactive governed by the laws of physics but the underlying equations are precise hard to solve.

This was besides the premise of the subject fabrication publication and aboriginal Netflix amusement ‘3 Body Problem’. An alien taxon inhabited a satellite successful a strategy with 3 suns orbiting each other, repeatedly starring to periods of clime chaos. The three-body occupation asks however 3 masses determination erstwhile each attracts the others by gravity. In classical mechanics, this occupation doesn’t person a wide closed-form solution, meaning there’s nary azygous look with which you tin foretell however the strategy volition germinate for each imaginable starting positions, speeds, and masses.

A looping path

The Chandrayaan-2 ngo ended successful partial nonaccomplishment erstwhile its lunar lander crashed connected the moon’s aboveground successful 2019. But since it had successfully launched an orbital module, which continued to orbit the moon, the Chandrayaan-3 ngo lone consisted of a propulsion module, a lander, and a rover.

After the lander and rover descended connected the satellite successful August 2023, the Indian Space Research Organisation (ISRO) moved the propulsion module to a 125,000 x 305,000 km orbit astir the world successful October. These 2 numbers are the distances from the world astatine the closest constituent (perigee) and farthest constituent (apogee) of the orbit.

So the propulsion module was looping astir the world connected a highly elliptical path: it came arsenic adjacent arsenic astir 125,000 km, past swung retired to astir 305,000 km, approaching the moon’s mean region (~384,000 km). That means it spent immoderate of its clip successful the moon’s gravitational neighbourhood.

The moon’s kick

When Dr. McDowell says it had “a tussle with the satellite successful November”, helium means the propulsion module had a comparatively adjacent walk by the moon. During a adjacent pass, the moon’s gravity tin kick, oregon abruptly change, the object’s velocity and absorption comparative to the earth. This is not similar friction oregon a collision but a purely gravitational interaction. Depending connected the geometry, the footwear tin rise the orbit, little it, tilt it oregon alteration its shape.

According to an ISRO statement successful November, the propulsion module entered the moon’s “sphere of influence” connected November 4 and exited it connected November 14. The organisation said it tracked the ‘event’ utilizing the Indian Deep Space Network (IDSN), a postulation of antennae adjacent Bengaluru that, unneurotic with information received by akin crushed stations operated by NASA and different abstraction agencies, monitors Indian assets successful space.

While it was successful the moon’s sphere of influence, the propulsion module flew by the satellite twice: connected November 6 it came wrong 3,740 km of the lunar aboveground and connected November 11 wrong 4,537 km.

After this encounter, the orbit of the propulsion module changed successful 3 ways. First, it became overmuch larger overall. According to ISRO the apogee jumped to 727,000 km; Dr. McDowell wrote successful his station connected December 30 that it was 983,000 km high. Either fig is good beyond the moon’s region and a motion that the moon’s propulsion added (or rearranged) orbital vigor successful the earth’s frame.

Second, the caller orbit has a antithetic signifier and orientation. ISRO concluded the perigee to beryllium 409,000 km and Dr. McDowell, 365,000 km. That is, the propulsion module nary longer comes backmost anyplace adjacent 125,000 km; it stays precocious astir each the time. And third, the orbit became noticeably tilted, by 22º, comparative to the earth’s equator. This happened due to the fact that the moon’s gravity pulled the module successful a absorption that wasn’t perfectly aligned with its existent question and orbital plane. As a effect the module’s angular momentum vector changed.

Very antithetic orbit

Per the statement, ISRO took “special attraction … to show its trajectory” and its proximity to different abstraction objects. “The wide outer show was mean during the flyby and nary adjacent attack was experienced with the different lunar orbiters. This lawsuit garnered invaluable insights and acquisition from ngo planning, operations, formation dynamics perspectives, and particularly enhanced the knowing of disturbance torque effects.”

In sum, ISRO near the Chandrayaan-3 propulsion module successful a wide world orbit that grazed the moon’s neighbourhood. In November 2025, the timing lined up specified that the satellite passed adjacent capable to powerfully tug connected the propulsion module. This reshaped its orbit, pushing it into a higher, much tilted, and much utmost ellipse. As a result, tracking teams present recovered it with a precise antithetic acceptable of orbital parameters.

In his post, Dr. McDowell credited amateur astronomer Sam Deen, astronomer Luca Buzzi, and Bill Gray, who developed notable bundle to way near-earth objects, “for figuring retired that the suspected asteroid CE1M9G2 … was really Chandrayaan-3”.