Space Docking Experiment (SpaDeX): Docking Event Updates and Discussion.

SpaDeX Docking event (third attempt) scheduled between 05:30-0700 (IST) / 00:00-01:30 (UTC), 12 January 2025 has been postponed. Standby for official update.

Live webcast: (Links will be added as they become available)

• ISRO Official (Private)
• DD National

SpaDeX-1 (2x 220 kg) : Space Docking Experiment or SpaDeX is a technology development mission to demonstrate rendezvous and docking capability in circular orbit and test other technologies relevant to future missions like Chandrayaan-4 (lunar sample return) and proposed Bharatiya Antariksh Station (BAS). It consists of two small satellites Spacecraft-A or SDX01 (chaser) and Spacecraft-B or SDX02 (target) weighing about 220 kg each. Following first mission another similar mission SpaDeX-2 can be undertaken in near future to demonstrate Rendezvous and Docking in elliptical orbit.

Objectives:

• Rendezvous and Docking using V-Bar (along velocity vector) approach
• Demonstrate power transfer between the docked spacecrafts
• Control one spacecraft from the Attitude Control System of other spacecraft in the docked configuration.
• Application based payload operations after undocking.

New technologies:

• Low-impact docking mechanism (Refer to this patent)
  • Androgynous, One Degree of Freedom, 450 mm diameter, 1 cm/s approach velocity
• Sensor suite:
  • Laser Range Finder (LRF) : Determining relative position and velocity (Range: 6000 to 200 m) using Corner Cube Retro Reflectors
  • Rendezvous Sensors (RS) : Determining relative position (Range: 2000 to 250 m and 250 to 10 m), uses Laser Diode targets
  • Proximity and Docking Sensor (PDS) : Determining relative position and velocity (Range: 30 m to 0.4 m), uses Laser Diode targets
  • Mechanism Entry Sensor (MES) : Detecting SDX01 (chaser) entry into SDX02 (target) during docking (Range: 8 cm to 4 cm)
• Power transfer interface
• Inter-satellite communication link (ISL) for autonomous communication between spacecraft.
• GNSS-based Novel Relative Orbit Determination and Propagation (RODP) processor.
• Rendezvous and Docking algorithms
• Simulation test beds for both hardware and software design validation and testing.

Docking process:

• SDX01 (chaser) and SDX02 (target) were injected into 470 km circular orbit with slightly different relative velocities to impart 10-20 km distance between them.
• SDX02 performs a drift arrest manoeuvre to hold inter-satellite separation at 10-20 km
• SDX01 (chaser) will incrementally reduce inter-satellite separation with holds at fixed distances (5 km, 1.5 km, 500 m, 225 m, 15 m, and 3 m) to evaluate the sensors and software performance.
• Docking and rigidization.

• Demonstration of inter-satellite power transfer.

• Spacecraft details : (Refer to this EoI)

• Bus : Extended Microsat bus

• Propulsion System:

  • Propellant Tank: 1× 7.5 litres (Hydrazine)
  • Thrusters: 1N (9 Nos)

• Power:

  • Battery: Li-ion cells pack, Capacity: 26 Ah
    
  • Solar Arrays : 528 W

• Attitude and Orbit Control System:

  • Reaction Wheels : 4 Nos
  • Magnetorquers: 3 Nos
    
  • Thrusters : 9 Nos

• TT&C:

  • S-band TM/TC with ranging functionality

Updates:

Fourth docking attempt:

Third docking attempt: (Aborted)

Second docking attempt: (Aborted)

First docking attempt: (Aborted)

Post undocking: After undocking, SDX01 and SDX02 will operate as independent satellites with their application centred payloads for an expected mission life of two years.

• SDX01 Payload:

  • High-Resolution Camera (HRC): Miniaturized surveillance camera by SAC/ISRO
    • IGFOV: 4.5 m
    • Swath: 9.2 × 9.2 km (snapshot mode) and 9.2 × 4.6 km (video mode)

• SDX02 Payload

  • Miniature Multi-Spectral Payload (MMX) by SAC/ISRO for vegetation studies.
    • 4× VNIR (450 to 860 nm) bands
    • IGFOV: 25 m
    • Swath: 100 km
  • Radiation Monitor (RadMon): To monitor harmful radiation during human spaceflight. (Note: SiC UV Dosimeter was flown on SSLV-D3/EOS-08 earlier)