The ISRO SpaDeX Mission has marked a historic achievement in India’s space exploration journey. On 16 January 2025, the Indian Space Research Organisation (ISRO) successfully demonstrated the docking of two satellites in Earth’s orbit. With this achievement, India became the fourth country in the world to demonstrate space docking technology, after the United States, Russia and China.
SpaDeX stands for Space Docking Experiment. The mission was launched on 30 December 2024 using the PSLV-C60 rocket from the Satish Dhawan Space Centre, Sriharikota. It involved two specially developed satellites, SDX01 (Chaser) and SDX02 (Target), designed to demonstrate rendezvous, docking and undocking operations in space.
This achievement is important for India’s future space programmes, including the Bharatiya Antariksh Station (BAS), Gaganyaan and Chandrayaan-4. It will also support future satellite servicing, orbital assembly and other advanced space exploration activities.
Key Highlights of ISRO SpaDeX Mission
- Mission Name: Space Docking Experiment (SpaDeX)
- Conducted By: Indian Space Research Organisation (ISRO)
- Launch Date: 30 December 2024
- Launch Vehicle: PSLV-C60
- Launch Location: Satish Dhawan Space Centre, Sriharikota
- Satellites: SDX01 and SDX02
- First Successful Docking: 16 January 2025
- Successful Undocking: 13 March 2025
- Second Successful Docking: 20 April 2025
- Power Transfer Demonstration: 21 April 2025
- Major Achievement: India became the fourth country to demonstrate space docking technology.
What is the ISRO SpaDeX Mission?
SpaDeX, or Space Docking Experiment, is an ISRO technology demonstration mission developed to test the ability of two small spacecraft to approach and connect with each other while orbiting Earth.
In simple terms, space docking is similar to connecting two moving vehicles. However, performing this operation in space is much more complicated because both spacecraft travel at high speeds and must maintain extremely accurate positions and velocities.
The SpaDeX mission was designed to demonstrate these operations using two independently operating satellites.
The main purpose was to develop indigenous technology for rendezvous, docking and undocking. These capabilities are essential for future missions involving space stations, lunar exploration, satellite servicing and human spaceflight.
Important Features of the SpaDeX Mission:
- Demonstrated indigenous space docking technology.
- Used two small satellites weighing approximately 220 kg each.
- Tested autonomous rendezvous and docking operations.
- Demonstrated electrical power transfer between docked spacecraft.
- Tested the ability to undock and operate satellites independently.
- Developed important technologies for India’s future space exploration programmes.
Important Details of the SpaDeX Mission
The following table provides the major technical and operational details of the mission.
| Particulars | Details |
| Full Form | Space Docking Experiment |
| Mission Name | SpaDeX |
| Space Agency | ISRO |
| Launch Date | 30 December 2024 |
| Launch Vehicle | PSLV-C60 |
| Launch Site | Sriharikota, Andhra Pradesh |
| Satellite 1 | SDX01 |
| Satellite 2 | SDX02 |
| SDX01 Role | Chaser |
| SDX02 Role | Target |
| Satellite Mass | Approximately 220 kg each |
| Planned Orbit | 470 km circular orbit |
| Orbit Inclination | 55 degrees |
| First Docking | 16 January 2025 |
| Undocking | 13 March 2025 |
| Second Docking | 20 April 2025 |
| Power Transfer | 21 April 2025 |
| Mission Organisation | ISRO |
PSLV-C60: Launch Vehicle Used for the SpaDeX Mission
The SpaDeX mission was launched on 30 December 2024 using the Polar Satellite Launch Vehicle (PSLV-C60).
PSLV is one of India’s most important and reliable launch vehicles. It has played a major role in launching Indian and international satellites into different Earth orbits.
For this mission, PSLV-C60 carried two SpaDeX satellites along with the PSLV Orbital Experimental Module (POEM-4).
The launch vehicle successfully placed the satellites into their intended orbital configuration, allowing ISRO to begin the planned rendezvous and docking experiments.
Important Facts About PSLV-C60:
- PSLV stands for Polar Satellite Launch Vehicle.
- PSLV-C60 was used for the SpaDeX mission.
- The mission launched two small spacecraft.
- It also carried POEM-4 with 24 experimental payloads.
- The launch took place from Sriharikota on 30 December 2024.
SDX01 and SDX02: Two Satellites of the SpaDeX Mission
The SpaDeX mission involved two specially designed satellites. Both satellites performed different roles during the docking experiment.
- SDX01 – Chaser Satellite
SDX01 was designated as the Chaser satellite. Its primary responsibility was to approach the target satellite and perform the docking operation.
It used navigation sensors, communication systems and propulsion technology to control its movement relative to the target spacecraft.
- SDX02 – Target Satellite
SDX02 was designated as the Target satellite. It provided the spacecraft with which the Chaser satellite had to establish a connection.
It was equipped with the necessary systems to support rendezvous, navigation and docking experiments.
| Satellite | Designation | Main Function |
| SDX01 | Chaser | Approaches and docks with the target |
| SDX02 | Target | Acts as the spacecraft to be approached |
Both satellites were equipped with indigenous technologies developed to demonstrate India’s space docking capabilities.
How Did the Space Docking Process Work?
Space docking requires extremely accurate coordination between two spacecraft. They must approach each other at controlled speeds and maintain the correct alignment before connecting.
The SpaDeX mission demonstrated this process through several important stages.
- Launch and Satellite Separation
On 30 December 2024, PSLV-C60 launched SDX01 and SDX02 into space. Both satellites were deployed into their planned orbit and began their independent operations.
- Rendezvous Operation
Rendezvous is the process of bringing two spacecraft close to each other while controlling their relative speed and position.
The two SpaDeX satellites gradually reduced their separation through carefully planned orbital manoeuvres.
- Relative Navigation
The spacecraft used specialised sensors and navigation systems to measure their relative position, distance and movement.
These measurements helped the Chaser satellite determine how to approach the Target safely.
- Close Approach
The Chaser satellite gradually approached the Target through different holding points.
The distance between the satellites was reduced in stages, including 15 metres and 3 metres, before the final docking operation.
- Successful Docking
On 16 January 2025, ISRO successfully completed the docking of SDX01 and SDX02.
The two spacecraft connected through their docking mechanisms and demonstrated India’s capability to perform an advanced orbital operation.
- Undocking Operation
On 13 March 2025, ISRO successfully undocked the two satellites.
This experiment demonstrated that the spacecraft could safely separate after docking and continue their independent operations.
Major Objectives of the SpaDeX Mission
The primary objective of the SpaDeX mission was to develop and demonstrate the technology required for autonomous rendezvous, docking and undocking of two small spacecraft.
Apart from its primary objective, the mission included several important technological demonstrations.
| Objective | Explanation |
| Rendezvous | Bringing two spacecraft close to each other |
| Docking | Connecting two spacecraft in orbit |
| Undocking | Separating docked spacecraft safely |
| Power Transfer | Transferring electrical power between connected satellites |
| Relative Navigation | Measuring the relative position and velocity of spacecraft |
| Autonomous Operations | Performing docking-related activities with onboard control systems |
| Payload Operations | Operating scientific payloads after undocking |
An important achievement was the successful demonstration of electrical power transfer between the two satellites on 21 April 2025.
During this experiment, ISRO successfully operated a heater element on one satellite using electrical power supplied by the other satellite. The power transfer was demonstrated in both directions.
This technology will be useful for future in-space robotics, satellite servicing and other advanced orbital operations.
POEM-4: 24 Experimental Payloads in the SpaDeX Mission
Another important component of the PSLV-C60 mission was POEM-4.
POEM stands for PSLV Orbital Experimental Module. It uses the spent fourth stage of the PSLV rocket as an experimental platform for conducting scientific and technological experiments in microgravity conditions.
Normally, the spent upper stage of a rocket may become space debris after completing its primary mission. However, ISRO converted the PSLV fourth stage into a platform for additional scientific experiments.
POEM-4 carried a total of 24 experimental payloads.
| Category | Number of Payloads |
| ISRO and Department of Space Centres | 14 |
| Non-Government Entities (NGEs) | 10 |
| Total Payloads | 24 |
These experiments covered several areas of scientific research and technology development, including:
- Space robotics and robotic manipulators.
- Green propulsion systems.
- Artificial Intelligence applications.
- Microgravity experiments.
- Advanced sensors and navigation technologies.
- Space communication systems.
- Biological and plant growth experiments.
- Synthetic Aperture Radar technology.
POEM-4 provided an opportunity for research institutions, startups and academic organisations to test their technologies in the space environment.
It successfully completed its experimental mission and re-entered Earth’s atmosphere on 4 April 2025 at 08:03 IST over the Indian Ocean.
Why Is Space Docking Technology Important for India?
Space docking technology is an essential capability for countries planning advanced space exploration missions.
Many future missions will require multiple spacecraft or modules to work together. Instead of launching all components together, different parts can be launched separately and connected in orbit.
The SpaDeX mission has created an important technological foundation for India’s future space programmes.
- Bharatiya Antariksh Station (BAS)
India plans to develop its own space station, known as the Bharatiya Antariksh Station.
Space docking technology will be essential for connecting different modules, spacecraft and cargo vehicles with the space station.
It will also support the transportation of astronauts, equipment and supplies.
- Gaganyaan Human Spaceflight Programme
The Gaganyaan programme aims to demonstrate India’s human spaceflight capabilities.
Advanced docking technology can support future crewed missions by allowing spacecraft to connect with orbital structures and other space vehicles.
It will also help ISRO develop important technologies required for more advanced human space exploration.
- Chandrayaan-4 Mission
Chandrayaan-4 is India’s planned lunar sample-return mission.
The mission involves complex operations and multiple spacecraft components. Space docking technology can support the joining of spacecraft modules and the transfer of materials during future lunar missions.
- Satellite Servicing and Refuelling
Space docking can support future satellite servicing operations.
Specially designed spacecraft may approach satellites to perform activities such as:
- Refuelling satellites.
- Repairing damaged components.
- Replacing selected equipment.
- Extending the operational life of satellites.
- Supporting the removal of space debris.
- Reduction in Mission Costs
Docking technology can allow different spacecraft components to be launched separately and assembled in orbit.
This approach may provide greater flexibility in planning large and complex space missions.
It can also help reduce dependence on launching a complete spacecraft in a single mission.
Countries That Have Demonstrated Space Docking Technology
With the successful SpaDeX mission, India became the fourth country to demonstrate space docking technology.
Before India, the United States, Russia and China had demonstrated this advanced capability.
| Country | Space Docking Achievement |
| United States | Demonstrated docking through early crewed spaceflight and orbital missions |
| Russia (Former Soviet Union) | Demonstrated docking through Soyuz and space station programmes |
| China | Demonstrated docking through its human spaceflight and space station programmes |
| India | Demonstrated docking through the SpaDeX mission in January 2025 |
This achievement represents an important development in India’s position in the global space technology sector.
Important Timeline of the ISRO SpaDeX Mission
The following timeline highlights the major events associated with the mission.
| Date | Event |
| 30 December 2024 | PSLV-C60 successfully launched the SpaDeX satellites |
| 16 January 2025 | First successful docking of SDX01 and SDX02 |
| 13 March 2025 | Successful undocking of the two satellites |
| 20 April 2025 | Second successful docking |
| 21 April 2025 | Successful demonstration of electrical power transfer |
| 4 April 2025 | POEM-4 safely re-entered Earth’s atmosphere |
ISRO SpaDeX Mission: Important Questions for Competitive Exams
The following facts are useful for SSC, RRB, UPSC, State PCS and other government examinations.
| Question | Answer |
| What is the full form of SpaDeX? | Space Docking Experiment |
| Which organisation conducted the SpaDeX mission? | ISRO |
| When was the SpaDeX mission launched? | 30 December 2024 |
| Which launch vehicle was used? | PSLV-C60 |
| Where was the mission launched from? | Sriharikota |
| What were the names of the two satellites? | SDX01 and SDX02 |
| Which satellite was the Chaser? | SDX01 |
| Which satellite was the Target? | SDX02 |
| When was the first successful docking completed? | 16 January 2025 |
| When was the first successful undocking completed? | 13 March 2025 |
| When was the second docking completed? | 20 April 2025 |
| When was power transfer demonstrated? | 21 April 2025 |
| How many countries had demonstrated space docking technology after India’s achievement? | Four |
| Which three countries demonstrated docking before India? | USA, Russia and China |
| What is the full form of POEM? | PSLV Orbital Experimental Module |
| How many payloads were carried by POEM-4? | 24 |
| How many POEM-4 payloads came from ISRO/DOS? | 14 |
| How many POEM-4 payloads came from Non-Government Entities? | 10 |
| What is the primary purpose of space docking? | Connecting two spacecraft in orbit |
Conclusion
The ISRO SpaDeX Mission is a major milestone in India’s space exploration programme. By successfully demonstrating the docking and undocking of two satellites, India became the fourth country in the world to demonstrate this advanced technology.
The mission also demonstrated indigenous navigation systems, autonomous spacecraft operations and electrical power transfer between docked satellites.
Its importance extends beyond a single technological experiment. Space docking will play a significant role in India’s future plans, including the Bharatiya Antariksh Station, Gaganyaan, Chandrayaan-4 and satellite servicing missions.
The successful completion of SpaDeX has strengthened India’s technological capabilities and created a foundation for more complex space exploration missions in the coming years.
