SpaDex mission is a cost-effective technology demonstrator mission, launched by the Indian Space Research Organization (ISRO), in December 2024. The mission was hailed with the successful launch of PSLV-C60 from Sriharikota. The launch is pivotal to the development of space technology in India. The Indian space economy was valued at $8.4 billion in 2023 and is anticipated to grow to $44 billion by 2033. The investments in the sector reached INR 1000 crore ($121.1 million) in 2023.
The PSLV-C60 vehicle will carry a pair of SPADEX satellites into an eastward orbit. It is the first Vehicle integrated up to the PS4 stage at PIF and moved to MST/FLP for satellite assembly and launch. The vehicle is 44.5 meters in height and offers 229 tons of lift-off mass. It features four propulsion stages, including S139, PL40, HPS3, and L1.6 (Ti).
The SPADEX spacecrafts namely Spacecraft A and Spacecraft B are built on an extended Microsat Bus, each with a mass of around 220 kg. The spacecraft are androgynous, that is, either of the spacecraft can act as a chaser (active spacecraft) during docking. They have solar panels, lithium-ion batteries, and a robust power management system. The Attitude and Orbit Control System (AOCS) includes sensors such as star sensors, sun sensors, magnetometers, and actuators such as reaction wheels, magnetic torques, and thrusters.
The technology is used for the demonstration of in-space docking using two small spacecraft launched by PSLV. The technology is pivotal to the various space missions of the country, such as India on the Moon, sample return from the Moon, the building and operation of Bharatiya Antariksh Station (BAS), and more. The technology is essential for multiple rocket launches to achieve common mission objectives. The launch of the mission makes India the fourth country in the world to have space docking technology.
SPADEX docking mechanism is motor-driven, featuring capture, extension/retraction, and rigidization mechanisms. It additionally features a power transfer connector mechanism for experimental power transfer post-docking and a video camera tilt mechanism for monitoring the docking process. The docking procedure takes place in multiple phases including initial separation and controlled drift, sequentially closer approach phases with, hold points for safety and control, and the final docking phase with capture, retraction, and rigidization.
The spacecrafts are equipped with payloads, for standalone mission phases after docking experiments. Spacecraft A contains a High-Resolution Camera (HRC) and Spacecraft B accommodates two payloads including a Miniature Multispectral (MMX) payload and Radiation Monitor (RadMon). The payloads are designed to provide high-resolution images, natural resource monitoring, vegetation studies, and on-orbit radiation environment measurements. However, the small size and mass of SpaDex, make it challenging for finer precision required for the rendezvous and docking maneuvers compared to docking two large spacecraft.
The primary objective of the SpaDex mission is to develop and demonstrate the technology needed for rendezvous, docking, and undocking of two small spacecraft (SDX01, which is the Chaser, and SDX02, the Target, nominally) in a low-Earth circular orbit. The secondary objectives additionally include a demonstration of the transfer of electric power between the docked spacecraft, composite spacecraft control, and Payload operations after undocking.
The mission is a combination of indigenous technologies, including, a docking mechanism, a suite of four rendezvous and docking sensors, power transfer technology, indigenous novel autonomous rendezvous and docking strategy, Inter-Satellite communication Link (ISL), incorporated with inbuilt intelligence, GNSS-based Novel Relative Orbit Determination and Propagation (RODP) processor, and simulation test beds.
In a nutshell, India is actively transforming its space footprint. The country is making an active shift from satellites used for communication and weather forecasting to advanced space technologies ideal for space exploration. The launch of SpaDex is one such initiative and the mission will be substantial to future missions.