India has been nationally admired for its immense success in the Space program. Not only has it crossed its boundaries for its innovation in space engineering, but it has also paved the way for launching a budget-friendly space mission. India has set remarkable milestones in ISRO's SpaDeX Mission and been successful in all space missions, such as Mangalyaan, Chandrayaan 2, Chandrayaan 3, Gaganyaan, and many more. Continuing its legacy, the Indian Space Research Organisation (ISRO) launched one more mission, SpaDeX, which stands for Space Docking Experiment.
This ISRO mission started on 30 December 2024 with the successful launch of the SpaDeX spacecraft using Polar Satellite Launch Vehicle (PSLV)-C60 from the Satish Dhawan Space Centre, Sriharikota. The docking mission was completed on 16 January 2025, making India the fourth country in the world to achieve this and placing it among the few nations with the ability to carry out space docking operations.
ISRO's powerful innovation achievement earned global recognition and made the nation proud. In this blog, I will walk you through the fantastic journey of the ISRO Space mission. We will explore in depth what the SpaDeX mission was about and how ISRO contributed technology and innovations that significantly impacted the success of this space mission.
ISRO’s SpaDeX Mission: India’s First Space Docking
SpaDeX ( Space Docking Experiment) is a technology demonstration mission developed by the Indian Space Research Organisation (ISRO) to mature and validate key in-orbit capabilities such as rendezvous (the process of bringing two spacecraft into proximity), docking (physically connecting two spacecraft), undocking (separating docked spacecraft), and formation flying (multiple spacecraft flying in coordinated orbits).
This mission involved two small identical satellites called SDX01 ( Chaser) and SDX02 ( Target ), each weighing around 220 Kg, based on a modified IMS-1 satellite platform.
They were launched aboard PSLV-C60 from the First Launch Pad at Satish Dhawan Space Centre on 30 December 2024 at 16:30:15 UTC. After being placed in slightly different orbits, SDX01 successfully executed a series of autonomous manoeuvres to approach and dock with SDX02, marking India’s first successful in-space docking using entirely indigenous technology.
These technologies, including human spaceflight, satellite servicing, sample return missions, lunar exploration, and the Bhartiya Antriksh Station (BAS) construction, are critical for future applications.
The spacecraft were designed and developed by UR Rao Satellite Centre (URSC), Bengaluru, with support from other ISRO centres, including VSSC, LPSC, SAC, IISU, and LEOS. Established in 1976, URSC is ISRO’s lead centre for designing, developing, assembling, and integrating communication, navigation, remote sensing, scientific, and small satellite missions.
What are the Objectives of the SpaDeX Mission
Now, let’s understand the key objectives of the SpaDeX mission in detail.
1. Develop and demonstrate technologies for rendezvous.
Rendezvous means bringing two spacecraft together (SDX01—Chaser, SDX02—Target), docking (connecting them) in space, and undocking (separating them) without human intervention in low Earth orbit.
2. Demonstrate power transfer between docked spacecraft
This is crucial for future missions involving in-space robots, modular space stations, or satellite servicing. One spacecraft might need to supply power to another that has limited or no power of its own
3. Showcase composite spacecraft control
When two spacecraft dock together, they form a single, larger structure. In this docked condition, they must move, turn, and stay stable in space as one combined unit. This is where composite spacecraft control comes into play. The attitude control system is the part of a spacecraft that controls its orientation or direction in space.
4. Verifying Independent Operation Post-Undocking
Verify that the spacecraft can act and function independently after undocking, just like how it was performing before docking, and also check that the systems remain stable and reliable, including power, communication, and control. After undocking, each spacecraft is expected to continue operating independently for up to two years.
5. Validate the V-bar approach for autonomous rendezvous and docking.
This means testing a specific path called the V-bar ( velocity vector) approach, where the Chaser spacecraft (SDX01) moves toward the Target (SDX02) along the direction of its orbital velocity (i.e., the same direction it’s moving around Earth).
What Were ISRO’s Key Contributions to the SpaDeX Mission?
Let me walk you through how ISRO made these significant innovations possible in the SpaDeX mission. From the indigenous docking mechanism to advanced navigation, communication, and testing infrastructure, highlights ISRO’s deep involvement and innovation in making SpaDeX successful.
These aren’t just technical components; they represent years of indigenous R&D by multiple ISRO centres working in unison, such as URSC, VSSC, LPSC, SAC, IISU, and LEOS.
1. Indigenous Docking Mechanism
ISRO used a specially designed docking system for the Spacex mission that allowed the two satellites to connect smoothly and gently, even at very low speeds ( just 10 mm per second). Safe and reliable docking will be very helpful for future missions like space stations or crew vehicles.
2. Advanced Rendezvous and Docking Sensors
- ISRO had used four specialised sensors for various purposes, covering multiple ranges, each handling a specific part of the approach for the SpaDeX mission like:
- Laser Rangefinder & Retroreflectors: This helped the spacecraft to measure distance and speed when they were about 6,000 meters to 200 meters apart.
- Rendezvous Sensors: This sensor takes over at medium distance and helps the Chaser get closer to the Target when they are about 2,000 to 10 meters apart.
- Proximity & Docking Sensors: This sensor operates when they are very close to each other, ensuring control during the final moments of docking
- Image Sensors: Captures visuals during final docking at range about 20 to 0.5 m Mechanism Entry Sensor: Detects final entry from 8cm to 4 cm apart ensuring smooth physical connection.
- Accelerometers & Star Trackers: Measures speed and direction, and keeps both spacecraft properly oriented throughout the approach and docking.
3. Power Transfer Technology
ISRO demonstrated the ability to transfer electric power between two satellites after docking.
This is a crucial feature for future missions where one spacecraft can transfer power to another, such as in modular space, space robotics, or satellite serving.
4. Autonomous Rendezvous and Docking Strategy
ISRO was able to perform docking without manual control from Earth
This process was guided by a specially developed Rendezvous and Docking Algorithm, which is thoroughly tested in ISRO’s advanced facilities.
- Rendezvous Simulation Lab – to model and refine the approach and docking steps
- Vertical Docking Experiment Lab – to test hardware and motion in a gravity-simulated setup.
- Docking Mechanism Performance Tests – to ensure the docking system works safely and reliably.
5. GNSS-Based Relative Navigation
ISRO used a special navigation processor called RODP (Relative Orbit Determination and Propagation), which was based on GNSS (Global Navigation Satellite System) data.
This helps each spacecraft accurately calculate the position and speed of its partner in real time, which is essential to autonomous docking.
6. Inter-Satellite Communication Link (ISL)
ISRO featured a VHF/UHF transceiver-based communication system that enabled two satellites (SDX01 and SDX02) to share their data in real time.
By integrating AI-driven state awareness, those two satellites could understand and respond to their partner's condition independently, ensuring smooth coordination during the autonomous docking process.
7. Trigger Capture Mechanism
ISRO used this mechanism to securely lock the Chaser onto the target during docking.
Before starting with power and data transfer, this system ensures that the two spacecraft are perfectly aligned and mechanically stable, providing a safe and reliable connection for further operations.
8. Simulation and Test Facilities
To ensure everything works perfectly in space, ISRO tested SpaDeX technologies using advanced ground facilities, such as Simulation test beds to validate both hardware and software, a Real test simulation environment to practice complex scenarios related to docking, and controlled lab setups to fine-tune algorithms and sensors in earth-like conditions.
9. Miniaturisation and Precision
ISRO performed docking using small satellites ( 220 Kg each ), which is more challenging and complex than docking large spacecraft. A smaller size requires highly precise movements and very accurate sensor performance with little room for error in control and alignment.
10. New Integration Process for PSLV Launch
ISRO launched SpaDeX using the new PSLV Integration Facility (PIF) instead of the traditional assembly buildings like VALF or MST.
This new process reduced the time needed for pre-launch preparations and is expected to increase launch efficiency and mission frequency for future PSLV missions.
Final Thoughts
ISRO has consistently pushed the boundaries of space exploration, demonstrating that impactful and successful missions can be achieved even with modest budgets. ISRO's SpaDeX Mission made a benchmark and opened doors for future missions, such as satellite servicing, space stations, and interplanetary exploration. This mission is a testament to ISRO’s ability to achieve great results even with limited resources, reinforcing India’s position as a key player in the global space community. ISRO’s contribution to the SpaDeX mission highlights the organisation’s exceptional ability to innovate and execute complex space technologies. Through the Indigenous development of docking systems, autonomous algorithms, and sensors, ISRO has proven its strength in tackling challenging space operations.
We have related Blog that gives you more information about what is in Trending like How India Will Tackle Global Trade Disruptions With Agile Policy, The Future of Web3: How Decentralization is Changing the Internet there are so many trending topics you need to know.
