Major milestone! India becomes 4th nation to dock satellites in orbit

India continues to prove out the abilities of its increasingly robust space program.

The two satellites of the Indian Space Research Organization‘s (ISRO) Space Docking Experiment, or SpaDex, successfully met up in Earth orbit yesterday (Jan. 15), making India just the fourth country to pull off an in-space docking. The other three are all heavy hitters in the space game: the United States, Russia and China.

“Spacecraft docking successfully completed! A historic moment,” ISRO said in an X post last night (Jan. 15). “Congratulations to the entire team! Congratulations to India!”

SpaDeX launched on an Indian PSLV rocket on Dec. 30, embarking on a mission to demonstrate the nation’s homegrown automated docking tech.

“This technology is essential for India’s space ambitions, such as Indian [missions] on [the] moon, sample return from the moon, the building and operation of Bharatiya Antariksh Station (BAS), etc,” ISRO officials wrote in a SpaDeX mission description. “In-space docking technology is essential when multiple rocket launches are required to achieve common mission objectives.”

BAS is an Earth-orbiting space station that India plans to assemble by 2035 or so. The nation is already working on a robotic lunar sample-return mission — Chandrayaan 4, which is targeted to launch in 2028.

Related: India launches 2 SpaDeX satellites on ambitious space docking test for future moon mission, space station

SpaDeX consists of two satellites, known as “Target” and “Chaser,” each of which weighs 485 pounds (220 kilograms). The duo were originally supposed to link up on Jan. 6, but ISRO pushed the attempt back several times to perform further tests and simulations.

Everything fell into place yesterday. Target and Chaser successfully maneuvered from 50 feet (15 meters) apart to just 10 feet (3 m), held at that close separation for a spell, and then completed the docking process, ISRO wrote in last night’s X post.

And things are still looking good, according to the agency.

“Post docking, control of two satellites as a single object is successful. Undocking and power transfer checks to follow in coming days,” ISRO wrote in another X post last night.

While the U.S., Russia, China and now India are the only nations to have docked spacecraft in orbit, the list of entities that have demonstrated docking and/or rendezvous tech extends beyond those borders.

For example, Japan and the European Space Agency (ESA) both built cargo spacecraft to service the International Space Station. ESA’s ATV freighters linked up to the orbiting lab by themselves, but Japan’s HTV ships needed a bit of help; they were captured by the station’s big robotic arm.

Michael Wall is a Senior Space Writer with Space.com and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, “Out There,” was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor’s degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.