'SpaDeX' Mission: How ISRO will dock two satellites in space

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The Indian Space Research Organisation (ISRO) is attempting to mate two satellites in the near vacuum of space, both of which would travel at a velocity ten times the speed of a bullet - a tough challenge to arrest two orbiting space assets and nudge them into a single spacecraft. It will take place under the 'SpaDeX' or Space Docking Experiment mission scheduled on December 30.


The mission is called 'space docking' and has been in the making for more than a decade in Bengaluru.


To date, only Russia, US, and China have mastered the complex technology and none share the intricacies of this process.

How ISRO will dock two satellites

The PSLV rocket will carry two specially designed satellites each weighing about 220 kg and then attempt docking and undocking at 470 kilometers above the Earth. The space agency will use a specially designed space docking mechanism called the 'Bhartiya Docking System' which meets the International Docking System Standard (IDSS) developed by NASA.


"India had to develop its own docking mechanism since no one shares the fine details of this hugely complex process," ISRO Chairman Dr S Somanath told News Agency.


Interestingly, ISRO has already taken a patent on the Indian docking mechanism.


The two satellites will be travelling at a velocity of about 28,800 kilometers per hour or about 36 times the speed of a commercial airplane or ten times the velocity of a bullet in the near-Earth orbit. Using specially designed rockets and a suite of sensors the relative velocities of the satellites will be slowed down to almost zero or just about 0.036 kilometers per hour or to 10 millimeters per second and then they will be mated together.


Two independent spacecraft, 'Chaser' and 'Target', will be conjoined to become one entity in space.


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"This sounds simple but to do this autonomously is a Herculean challenge as the physics involved is complex since both satellites have to remain in orbit and more importantly not crash into each other," Dr Somanath said.


"Mastering docking is a necessary step if India has to send Chandryaan-4, build a space station, and then send an Indian to the moon...SpaDeX is one mission with many-many objectives, truly the fullest use of tax payer money to innovate and catapult India into the next league of space fairing nations," he added.


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According to ISRO, SpaDeX mission is a cost-effective technology demonstrator mission for the demonstration of in-space docking using two small spacecraft launched by PSLV. This technology is essential for India's space ambitions such as Indian on the moon, sample return from the moon, and the building and operation of Bharatiya Antariksh Station (BAS), among others. In-space docking technology is essential when multiple rocket launches are required to achieve common mission objectives.


The SpaDeX mission was conceived and designed by scientists at ISRO but the final assembly, integration, and testing of the satellite was done at Ananth Technologies - a Bengaluru-based space technology company started in 1992 by an ex-ISRO employee turned entrepreneur Dr Subba Rao Pavuluri.


"It was a bold move to let a private company undertake this complex job but they came out with flying colors," Dr M Sankaran, Director, UR Rao Satellite Center, Bengaluru, said.


The Bhartiya Docking System is so sophisticated and more modern that in its current avatar, it uses only two motors compared to the 24 motors used in the IDSS. In its current format, it is only 450 millimeters in diameter but the final goal will be to develop an 800 millimeter-diameter docking port that will connect the Indian Gaganyaan Crew Module to the Bhartiya Antariksha Station.


The docking experiment is likely to be done by early in the New Year, Dr Sankaran said.


Through this mission, India is marching towards becoming the fourth country in the world to have space docking technology.