What is Rendezvous? what is Docking Technology?

What is Rendezvous?

• Rendezvous refers to the process of two spacecraft meeting in orbit and positioning themselves within close proximity for docking.
• It is achieved through careful calculations of orbital mechanics, propulsion adjustments, and precise navigation.

Rendezvous Process in SpaDeX

1. Initial Separation:
   The Chaser and Target spacecraft are released into slightly different orbits by PSLV, with a relative distance of 10–20 km.
2. Far Rendezvous:
   • Using small velocity corrections, the Chaser spacecraft approaches the Target.
   • The process reduces the inter-satellite distance in increments (e.g., 5 km → 1.5 km → 500 m → 3 m).
3. Final Approach:
   • At close distances, fine adjustments are made to ensure alignment.
   • Proximity sensors and algorithms guide the Chaser to the docking interface.

Docking Technology:

1. Docking Mechanism:
   • A low-impact docking system ensures the approach velocity remains at 10 mm/s to prevent damage.
   • The mechanism is androgynous (identical on both spacecraft) and peripheral, meaning docking can occur from multiple angles.
   • It uses a compact 450 mm docking interface, smaller but more precise than international systems.
2. Post-Docking Operations:
   • Demonstration of electric power transfer between the docked spacecraft.
   • The spacecraft undock and begin independent operations for the remainder of their mission life.

Key Technologies Enabling Rendezvous and Docking

1. Autonomous Rendezvous and Docking (ARD) Algorithms:
   • Algorithms like V-bar strategy, n-Pulse, Glideslope, and PV Guidance ensure precision in relative velocity and position adjustments.
2. Sensor Suite:
   • Laser Range Finders (LRF): Measures distance between spacecraft from 6000 m to 200 m.
   • Rendezvous Sensors (RS): Provides relative position and orientation data at close ranges.
   • Proximity and Docking Sensors (PDS): Tracks precise positions from 30 m to 0.4 m.
3. Inter-Satellite Communication Link (ISL):
   • Facilitates autonomous communication between Chaser and Target for status updates and control.
4. GNSS-Based Relative Orbit Determination:
   • Accurate relative positioning using GNSS signals and novel Relative Orbit Determination and Propagation (RODP) processors.
5. Simulation Test Beds:
   • Hardware-in-loop and software-in-loop simulations for validating docking strategies and sensor calibration.

Significance of RVD Technology

1. Applications in Space Exploration:
   • Supports modular assembly of space stations.
   • Enables lunar and interplanetary missions, including cargo transfer and human spaceflight.
2. Cost and Efficiency:
   • Reduces the need for large, single-launch payloads.
   • Allows for multi-launch strategies where spacecraft parts dock in orbit.
3. Global Competitiveness:
   • Positions India among a select group of nations with autonomous docking capability, including the US, Russia, and China.
4. Future Missions:
   • Essential for projects like Chandrayaan-4, Bharatiya Antariksh Station, and sample-return missions.

By mastering rendezvous and docking technology through the SpaDeX mission, ISRO is setting the stage for ambitious space endeavors and contributing to India’s leadership in space innovation.