![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2024\/12\/PSLV-CA-vehicle-is-transported-to-the-pad-in-advance-of-the-SPADEX-mission-Credit-ISRO-scaled.jpg\"){kind=spacer}
<\/p>\nThe Indian Space Research Organisation (ISRO) has launched a space docking experiment \u2014 a critical mission for India\u2019s upcoming human spaceflight campaign. The mission will demonstrate the technology to rendezvous, dock, and undock in orbit. The successful completion of the mission will be a key step towards India\u2019s ambitions for future missions to the lunar surface and the construction of an orbiting space station. It would also make India the fourth country to develop space docking technology.<\/p>\n
Meanwhile, exactly ten years after the first launch of a test crew module, assembly has begun on the human-rated launch vehicle that will one day launch crew to orbit as part of India\u2019s Gaganyaan program.<\/p>\n<\/p>\n
ISRO\u2019s Space Docking Experiment mission, or SpaDeX, successfully lifted off from the First Launch Pad at the Satish Dhawan Space Center in Sriharikota, India, on Monday, Dec. 30, at 16:30 UTC. A Polar Satellite Launch Vehicle (PSLV) rocket carried a pair of satellites for this experiment, each massing 220 kg, to a circular low-Earth orbit at 470 km, inclined 55 degrees.<\/p>\n
<\/p>\n
PSLV-60 vehicle is transported to the pad in advance of the SpaDeX mission. (Credit: ISRO)<\/p>\n
The PSLV is India\u2019s third-generation medium-lift launch vehicle and the first to adopt liquid stages. Due to the low mass of the payloads, this mission utilizes the PSLV-CA (or Core Alone) configuration. This variant omits the six strap-on boosters used on the standard PSLV-G and extended PSLV-XL versions and usually flies with less propellant in its upper stage.<\/p>\n
The vehicle\u2019s fourth stage utilizes storable liquid engines that can be reignited several times in orbit to release its payloads. This mission also carried the PSLV Orbital Experimental Module (POEM) platform, enabling experiments to be conducted, drawing its energy from a lithium-ion battery and solar panels around the fourth stage\u2019s tank. This platform was last used on Jan. 1, 2024, on the XPoSat mission.<\/p>\n
SpaDeX docking demonstration<\/p>\n
The SpaDeX experiment will be conducted around 10 days following launch when the two satellites, the SDX01 \u201cChaser\u201d and the SDX02 \u201cTarget,\u201d will be released with a small relative velocity between them. The pair will drift apart for around a day until they are separated by a distance of around 10 to 15 km. Once achieved, Target will eliminate the velocity difference between itself and Chaser using its propulsion system. The pair will then enter a health check period while orbiting around 20 km apart in what is referred to as a \u201cFar Rendezvous.\u201d Chaser will then begin incrementally moving closer to Target, first to five kilometers and then to 1.5 km, gradually decreasing the distance between them to three meters.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2024\/12\/spadex_craft_and_docked-illustration-Credit-ISRO.jpg\")
<\/p>\n
Diagram of the SpaDeX spacecraft (left) and the pair docked (right). (Credit: ISRO)<\/p>\n
Approaching each other at around 10 mm per second, the pair will eventually perform a controlled docking using four rendezvous and docking sensors. These include laser range finders and corner cube retro reflectors to determine relative range. At the same time, laser diodes facilitate the Proximity and Docking Sensor (PDS) from 30 m away to the final approach. A Mechanism Entry Sensor (MES) detects contact in the last eight centimeters, and the event will also be captured using an onboard video camera.<\/p>\n
The androgynous system, identical on both spacecraft, is similar to the International Docking System Standard (IDSS) used on the International Space Station and its visiting spacecraft. With one degree of freedom, it is smaller than the 800 mm IDSS at 450 mm and has only two motors compared to the 24 on the IDSS hexapod system.<\/p>\n
Secondary objectives for the mission include demonstrating electric power transfer between the two docked craft \u2014 a capability that will be particularly relevant for future robotics missions. Composite spacecraft control, where one craft controls the attitude of the other while docked, will also be demonstrated. The pair will then finally demonstrate an undocking maneuver and perform payload operations, after which they are expected to remain in operation for up to two years.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2024\/12\/The-SPADEX-craft-before-integration-with-the-PSLV-vehicle-Credit-ISRO.png\")
<\/p>\n
The SpaDeX craft during assembly and testing. (Credit: ISRO)<\/p>\n
Developed by ISRO\u2019s UR Rao Satellite Centre (URSC) in Bangalore, the two satellites will use a differential Global Navigation Satellite System (GNSS) for positioning. The onboard Novel Relative Orbit Determination and Propagation (RODP) processor determines Chaser and Target\u2019s relative position and velocity. This technology will pave the way for lunar missions where spacecraft cannot use GNSS, which would rely on Earth-based receivers for autonomous docking or undocking. The planned Chandrayaan-4 mission to the Moon will require multiple docking maneuvers of this kind. For the SpaDeX mission, however, the ground stations within the ISRO Telemetry, Tracking, and Command Network (ISTRAC) will be controlling the satellites while in orbit.<\/p>\n
Additional payloads<\/p>\n
A total of 24 additional payloads accompanied the primary mission as part of the aforementioned POEM-4 experimental module. POEM acts as a satellite bus with power generated by solar panels, providing all necessary subsystems for the experimental payloads onboard. These include the Micro Orbital Infrastructure Technology Demonstration (MOI-TD) by TakeMe2Space, described as India\u2019s first satellite lab in space, offering a platform for researchers and students to conduct experiments in microgravity.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2024\/12\/MOI-TD-tecb-demonstration-of-an-AI-labe-in-space-undergoing-final-testing-Credit-TakeMe2Space.jpeg\")
<\/p>\n
MOI-TD tech demonstration of an AI-lab in space undergoing final testing. (Credit: TakeMe2Space)<\/p>\n
The company is building affordable satellite infrastructure hosting AI-powered computer and storage services in low-Earth orbit (LEO). TakeMe2Space previously collaborated with ISRO to create the Radiation Shielding Experiment Module (RSEM), which launched on the XPoSat mission in January. The mission employed its innovative radiation-shielding coating in various thicknesses and saw the coating exposed to multiple C-class and X-class solar flares while in orbit. The coating demonstrated a 10x reduction across the range in Total Ionisation Dosage (TID) and will benefit satellite builders using non-radiation-hardened electronics in their circuits.<\/p>\n
The SpaDeX mission will test a new radiation monitoring system mounted in the SDX02 Target craft. The system estimates electron and proton radiation, which will inform the development of radiation monitoring instruments on future missions and protect astronauts and equipment.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2024\/12\/L-to-R-the-POEM-platform-with-Varuna-in-position-close-up-of-Varuna-Credit-Piersight.jpg\")
<\/p>\n
POEM platform with Varuna in position (left) and a close-up of Varuna (right). (Credit: Piersight)<\/p>\n
PierSight\u2019s Varuna will demonstrate synthetic aperture radar (SAR) in a cubesat form factor. Mounted to the POEM platform for this demonstration, Varuna will test the electronics, study the deployable antenna, and test the pre-driver stage of the solid-state power amplifier onboard. The mission will prove the flightworthiness of the subsystems and reach its highest level of technical readiness. The company aims to build a constellation that would monitor oceans with a 30-minute revisit time, providing information on oil spills and illegal fishing, amongst other maritime operations and security usages.<\/p>\n