A crucial component of mission planning is selecting the orbit for satellite docking, especially when human missions are involved. The significance of orbital parameters in supporting effective docking operations is highlighted by recent advancements, such as India’s SpaDeX (Space Docking Experiment) mission.
Low Earth Orbit (LEO): The majority of docking missions are carried out in LEO, usually at elevations between 300 and 600 kilometers. For instance, the SpaDeX mission functions at a circular orbit of roughly 470 kilometers, which makes it simpler to reach space and make rendezvous with other spacecraft easier.
Another crucial factor is the orbit’s inclination. Launched into a 55-degree inclined orbit, SpaDeX can cover a range of latitudes and is appropriate for a number of missions.
The relative velocity of the spacecraft involved must be precisely controlled during docking. Usually positioned in a somewhat lower orbit than the “target” satellite, the “chaser” satellite can catch up because of its higher velocity at lower altitudes. With controlled maneuvers, the chaser in SpaDeX steadily closes the gap to the target after an initial separation of 10–20 kilometers post-launch, eventually reaching a docking distance of just a few meters.
For human missions, autonomous docking mechanisms must be developed. Without direct human assistance, these technologies maneuver and dock using sophisticated sensors and algorithms. To guarantee precise location during docking maneuvers, SpaDeX makes use of a variety of sensors, such as proximity sensors and laser range finders.
Future human spaceflight missions will be significantly impacted by the developments in docking technology:
Multiple modules will need to dock in space for missions that are intended to build space stations, such as India’s proposed Bharatiya Antariksha Station. Autonomous docking will expedite this procedure and improve security.
To return samples to Earth, future lunar missions like Chandrayaan-4 will need to make several docking maneuvers between different modules (such as landers and propulsion modules). These intricate processes are made possible by successful demonstrations such as SpaDeX, which validate the technology needed for autonomous docking independent of Earth-based navigation systems.
The skills gained from these trips can also be applied to satellite servicing in orbit, where it could be necessary for one spacecraft to dock with another in order to perform repairs or upgrades.
In order to support future human missions and advance space exploration capabilities, the selection of orbit for docking satellites is impacted by a number of criteria, including altitude, inclination, relative velocity management, and the requirement for autonomous technology.
India’s Indian Space Research Organisation (ISRO) is planning additional docking attempts with its SpaDeX satellites based on the fuel availability in the spacecraft. The SpaDeX mission, which successfully launched two small satellites on December 30, 2024, is a critical step towards India developing its space docking technology, a capability currently held by only a few countries including the US, Russia, and China.
