ISRO Detects Chandrayaan-3 Module Re-Entering Moon’s Sphere of Influence

In November 2025, ISRO tracked a remarkable event: the propulsion module (PM) of Chandrayaan-3, which had long since moved away from the Moon, naturally drifted back into the Moon’s gravitational domain.

This re-entry (or re-encounter) is highly unusual in space missions. The module returned without any engine burns, purely under the influence of gravity from the Earth, Moon, and Sun.

Such a gravitational flyby provides ISRO and planetary scientists with a unique natural experiment — delivering new insights into orbital mechanics, three-body dynamics, and long-term spacecraft behavior.

This article explores the Chandrayaan-3 mission context, the mechanics of the module’s return, how ISRO tracked it, and what this episode means for the future of space exploration.

Background: Chandrayaan-3 Mission

Mission Objectives

Chandrayaan-3 was launched in July 2023, with key objectives including a soft landing near the Moon’s south pole, rover exploration, and in-situ scientific measurements.
The mission comprised three main components: the lander (Vikram), the rover (Pragyan), and the propulsion module (PM).
While the lander and rover completed their surface mission, ISRO also designed a post-landing plan for the PM, making intelligent use of its residual fuel for extended mission utility.

Propulsion Module Role

The PM was responsible for carrying the lander and rover to lunar orbit and supporting them until separation.
Importantly, after the lander and rover separated, the PM retained a substantial amount of fuel — more than initially expected.
ISRO’s flight-planning team used this surplus to propose a bold strategy: re-orbit the PM away from the Moon and into a stable Earth-bound orbit, rather than letting it become space debris.

SHAPE Payload

Onboard the PM is a specialized scientific instrument called SHAPE (Spectro-polarimetry of Habitable Planet Earth).
SHAPE is designed to observe Earth from space, specifically to study the polarization of Earth’s light in near-infrared wavelengths.
These observations help in understanding how Earth would look as a potentially habitable exoplanet, and provide data on atmospheric properties and reflectivity.

How the Propulsion Module Was Returned to Earth Orbit

Maneuvers After Lunar Mission

In October 2023, ISRO performed a Trans-Earth Injection (TEI) maneuver, moving the PM from lunar orbit to a high Earth orbit.
Before TEI, ISRO executed a maneuver to raise the PM’s apolune (its furthest point in orbit) significantly, increasing its orbital period — a carefully planned step to maximize efficiency and use of remaining fuel.
This strategy was driven by multiple goals: ensure collision avoidance (both with the Moon and with Earth’s geostationary belt), prolong the life of the PM, and leverage the SHAPE payload for further science.

Flybys During Return

During its Earth-transfer trajectory, the PM executed four flybys of the Moon, using gravity to shape its path and reduce propellant consumption.
These flybys allowed ISRO to test precise navigation, orbital prediction tools, and long-term mission planning strategies.
By early November 2023, the PM exited the Moon’s Sphere of Influence, settling into a stable and highly elliptical Earth orbit.

Stable Earth Orbit

After the TEI and flybys, the PM’s new orbit had a long period (almost two weeks) and a high apogee.
ISRO carefully predicted and confirmed that within this orbit, the PM posed no immediate threat to active Earth satellites, thanks to its trajectory and perigee (closest point to Earth) parameters.
Meanwhile, SHAPE continued its operations whenever the geometry permitted — particularly when Earth entered its field of view.

The 2025 Re-Entry into the Lunar Zone

Prediction of Return

In September 2025, data from asteroid-tracking networks indicated that the PM’s trajectory would naturally bring it back near the Moon.
Importantly, this prediction was not the result of a planned burn or maneuver by ISRO; rather, it was due to the passive drift of the module under gravity.
Analysts realized the module could cross into the Moon’s gravitational dominance — known as the Moon’s Sphere of Influence (SOI) — again, triggering potential flybys.

Entering the Moon’s Sphere of Influence

On 4 November 2025, the PM crossed into the Moon’s SOI. In this region, the Moon’s gravity begins to dominate over Earth’s, significantly altering the PM’s motion.
Once inside this domain, the PM became subject to a stronger lunar pull, which influenced its orbit in new ways.

First Flyby: November 6, 2025

The first close approach happened on 6 November, when the PM came within about 3,740 kilometers of the lunar surface.
This event occurred outside the visibility window of India’s Deep Space Network, limiting real-time data collection, but the approach was still confirmed by orbital tracking.
Despite limited direct contact, the flyby provided crucial information about how the PM’s orbit evolved under natural gravitational forces.

Second Flyby: November 11, 2025

The second flyby occurred on 11 November, with the PM coming to a distance of approximately 4,537 kilometers from the Moon.
This time, the flyby was within range of ISRO’s telemetry and tracking network (ISTRAC), allowing more detailed monitoring.
Across both flybys, ISRO reported that the satellite’s performance remained normal, with no signs of malfunction and no threat to other orbiters.

Changes in Orbital Dynamics

Orbit Size and Shape

Before re-entry, the PM was in an orbit of roughly 100,000 km × 300,000 km (periapsis × apoapsis).
After the flybys, its orbit expanded dramatically to about 409,000 km × 727,000 km, showing the significant impact of lunar gravity.
This dramatic change underscores how powerful gravitational interactions can be — even without active propulsion.

Inclination Shift

Along with a change in size, the orbital plane of the PM shifted. Its inclination (tilt with respect to the Moon’s orbit) dropped from about 34° to 22°.
Such a shift indicates that the flybys not only changed how far the module traveled, but also the orientation of its path.

Three-Body Dynamics

The PM’s journey is a textbook example of the three-body problem in celestial mechanics: the module is simultaneously influenced by Earth, Moon, and even the Sun.
Because of this interplay, the PM’s path was not straightforward — its orbit evolved naturally under competing gravitational pulls.
This natural drift, without active thrusting, is a valuable demonstration of gravity-assisted orbital evolution.

ISRO’s Tracking and Monitoring

Role of Ground Stations (ISTRAC)

ISRO’s Telemetry, Tracking, and Command Network (ISTRAC) played a key role in observing and verifying the flybys.
During the second flyby especially, ISTRAC maintained regular contact, tracking the PM’s precise position, velocity, and attitude.
This level of monitoring was critical not only for safety but also for gathering high-quality data on the flyby dynamics.

Telemetry Data & Performance

Throughout both flybys, ISRO collected telemetry to assess how the PM responded to gravitational forces.
The module was reported to be in nominal condition, meaning that despite the unplanned re-entry, there were no critical anomalies or degradation.
ISRO’s teams used this data to validate their models of orbital dynamics and disturbance torques (forces that can slowly twist or tilt a spacecraft’s orientation over time).

Safety Considerations

One of ISRO’s priorities was to ensure that during these close approaches, the PM did not pose any risk to other lunar orbiters or to itself.
By continuously tracking and analyzing its trajectory, ISRO confirmed that no dangerous proximities occurred.
This careful monitoring underscores ISRO’s maturity in managing space operations — even for a module that was not initially intended to return to the Moon.

Scientific and Engineering Implications

Validating Orbital Models

This flyby event gives ISRO real-world data to test and refine its orbital-prediction models.
Engineers and scientists can compare observed behavior with simulations, improving future mission design and prediction accuracy.
Such validation is especially valuable for missions involving weak stability boundary trajectories, gravity assists, or long-duration passive orbits.

Fuel-Efficiency and Mission Design

The re-entry shows that spacecraft do not always need active propulsion to alter their orbits — gravity can do a lot of work.
Future missions (especially deep-space or multi-body missions) can exploit passive gravitational interactions to reduce fuel usage and increase mission flexibility.
This could be especially helpful for sample-return missions, long-term orbital staging, or spacecraft parked in high orbits.

Extended Use of Mission Hardware

The PM’s long-term survivability and continued trackability highlight how mission elements can be reused or repurposed.
Instead of discarding the propulsion module, ISRO extended its service, using leftover fuel to continue scientific observations (via SHAPE) and orbital exploration.
This strategy increases the mission return on investment and reduces space debris.

Enhancing Space Sustainability

By closely tracking and managing an otherwise “spent” module, ISRO demonstrates responsible space stewardship.
Such practices contribute to space situational awareness (SSA): understanding where objects are, how they move, and what risks they pose.
Ensuring long-term monitoring of old mission components helps avoid future collisions and clutter in valuable orbital regimes.

Challenges and Risks

Communication Constraints

The first flyby occurred when the PM was outside reliable visibility for India’s Deep Space Network, limiting real-time data.
Such gaps in communication can reduce the fidelity of telemetry and make precise orbit determination harder.

Predictability and Modeling

Natural drift under multi-body gravitational influence is inherently less controllable than powered maneuvers.
Small perturbations — such as solar radiation pressure, slight asymmetries in mass distribution, or even micro-thrusts — can compound over time, making long-term prediction challenging.
Maintaining accurate models requires constant updating, data assimilation, and validation.

Resource Demand

Tracking a spacecraft for years after its main mission ends demands significant ground station time, analysis, and manpower.
ISRO must balance these demands with other priorities — especially when the spacecraft is not actively performing high-value science.

Potential Future Risk

Though no collision risk was reported during the 2025 flybys, the evolving orbit means that future encounters (with other spacecraft or with the Moon or Earth) cannot be ruled out.
Long-term, the PM might drift into other gravitational regimes or even become unstable, emphasizing the need for continuous monitoring.

Broader Impacts

Strengthening ISRO’s Capabilities

This natural re-entry enhances ISRO’s reputation as a world-class space agency capable of advanced mission planning, orbital design, and long-term operations.
It demonstrates not just the ability to land on the Moon, but also to manage and reuse mission assets intelligently.

Scientific Value for Education and Research

The flyby provides a real-world case study for students, researchers, and mission planners studying three-body dynamics, gravitational perturbations, and long-duration orbital behavior.
Universities and research institutions can use this data to teach and drive innovation in space mechanics and mission design.

Policy and Sustainability Message

By responsibly tracking and leveraging the PM, ISRO sends a strong signal about its commitment to sustainable space practices.
Such an approach helps build global confidence that India is not only exploring space but doing so responsibly and safely.

Implications for Future Missions

Future lunar or deep-space missions can incorporate gravitational passives, like what Chandrayaan-3’s PM experienced, into their design.
Gravity-assisted planning, fuel savings, and long-term tracking could become more common in ISRO’s mission architecture.
This episode could directly influence designs for sample-return missions, platforms in high lunar or Earth orbits, or even multi-body trajectory missions.

Looking Forward: Future Prospects

Possible Additional Flybys

Given the updated orbit, there is potential for further lunar encounters in the future. Some analysts suggest another close approach could happen around mid-2026.
Continued tracking will help verify these predictions, and if they materialize, ISRO could again gather useful data.

Use of Remaining Fuel (If Any)

If any propellant remains, ISRO could consider small corrective maneuvers — though the decision would depend on trade-offs between risk, benefit, and fuel cost.
Even small thrusts could adjust the PM’s orbit for better scientific geometry or safer paths.

Reactivating Scientific Missions

If SHAPE (the onboard instrument) is still operable, ISRO might attempt to re-activate it when conditions are favorable.
More Earth observations, based on polarization or spectroscopy, could further enrich our understanding of how our planet appears from space.

Enhancing Mission Design Tools

The data from these flybys can feed into ISRO’s simulation and trajectory-design tools, making future missions more precise and fuel-efficient.
Engineers will likely refine algorithms for gravity-assisted trajectories, weak-stability boundary trajectories, and orbit-shaping maneuvers.

Scaling Sustainability

This re-encounter sets a precedent: mission hardware does not have to be abandoned or left unmonitored.
ISRO can formalize strategies for post-mission tracking, re-orbiting, or even repurposing spacecraft — contributing to a more sustainable orbital environment.