As the year began, the Indian Space Research Organization will end its main Spadex mission – the launch of two small satellites to demonstrate docking in space – from the country’s first launch pad on December 30 at 9:58 pm. The only spaceport at Sriharikota. Docking is a process where two satellites are aligned and then joined in space — a requirement for missions the space agency hopes to achieve in the future, such as Chandrayaan-4 or setting up the Indian space station.
The Spadex mission will see two satellites – SDX01 or the chaser and SDX02 or the target – align in the same orbit, reduce the distance between each other, connect and transfer electrical power between them, and then separate. After they separate, the payloads on board will continue to operate for two years.
India’s workhorse Polar Satellite Launch Vehicle PSLV-C60 will launch two 220 kg satellites into a 470 km circular orbit, with the launch vehicle imparting a small relative velocity between the two. Within a day, the two satellites will be built within a distance of about 10 to 20 km from each other.
The propulsion system on the target satellite will then be used to prevent the satellites from moving further away. Which means both satellites will move at the same speed at a separation of 20 km – a phase known as ‘distant rendezvous’. The chaser satellite will then continue to approach the target satellite, successively reducing the distance between them to 5km, 1.5 km, 500 m, 225 m, 15 m, 3m and then docking together.
Once the satellites are docked, electrical power transfer between the two will be performed. They will demonstrate control of both spacecraft together. The satellites will then separate and begin operating their payloads.
The Chaser or SDX01 satellite has a high-resolution camera on board — a smaller version of a surveillance camera. The target or SDX02 satellite will carry a multispectral payload that will carry a radiation monitor used to monitor natural resources and vegetation, as well as study space radiation and create a database. Due to the smaller size and mass of satellites, docking is more challenging, requiring better precision than with larger spacecraft.
The end of the year will be a mission of many firsts. The satellites will use several new technologies such as a docking mechanism, a suite of sensors that will allow the satellites to approach and dock instead of crashing together, and a novel navigation constellation-based relative orbit determination and propagation processor.
The rocket’s final stage will be used to demonstrate 24 payloads, including a robotic arm to capture space debris and up to two leaves in space to demonstrate seed germination and plant growth.
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