Indian space agency Isro has for the first time successfully conducted space docking by joining together two small craft in space.

The technology is essential for the country’s future ambition to build an Indian space station and put a person on the Moon.

The mission called SpaDeX blasted off from Sriharikota launch pad in southern India on 30 December. The two spacecraft, launched on a single rocket, separated in space. The docking process, initially scheduled for 7 January, was rescheduled a number of times.

On Thursday morning, the space agency announced that it had created history by becoming only the fourth country in the world with such technology after United States, Russia and China.

Prime Minister Narendra Modi was at the Isro office in Bangalore as scientists carried out the test.

“It is a significant stepping stone for India’s ambitious space missions in the years to come,” he later posted on X.

Federal Science Minister Jitendra Singh expressed relief that the docking had “finally” happened.

The two spacecraft on SpaDeX (short for Space Docking Experiment) are called SDX01 or the Chaser and SDX02 or the Target. Each weigh about 220kg (485lbs) and since their launch, they were travelling in space at a carefully chosen speed.

“They were thrown into space together but at the time of separation, they were placed with different velocity to allow them to build a distance of 10-20km between them,” Mila Mitra, a former Nasa scientist and co-founder of Delhi-based space education company Stem and Space, told the BBC.

“During docking, scientists manoeuvred them to close that distance allowing them to mate,” she added.

The docking was initially scheduled for 7 January, but Isro later delayed it by two days saying they “needed to carry out some more testing through simulations” before the actual docking.

The second time, it said there had been a glitch while trying to bring the satellites closer, but added that the spacecraft were safe.

On Sunday, Isro said scientists had managed to reduce the distance between the Chaser and the Target first to 15metres and then to 3metres. They said after the trial attempt, the spacecraft were “moved back to safe distance” and that they were analysing data.

S Somanath, who was Isro chief when SpaDeX (short for Space Docking Experiment) was launched and was monitoring its progress until his retirement a few days ago, had described docking as “a very complex process” that needed extreme precision and coordination.

To begin with, the two spacecraft had to be in the same orbit so that the Chaser could start to approach the Target.

On Thursday morning, scientists began by gradually reducing the speed of the two spacecraft – bringing them ever closer until they were just 3 metres apart. Then their connectors were latched together.

In the next step, the two spacecraft were screwed on perfectly, creating an airtight passage for safe transfer of material or crew, completing space docking.

An Isro official told the BBC that over the next two-three days, the mission will carry out what is being billed as one of its most important experiments – it will transfer electrical power from the Chaser to Target.

This, Ms Mitra, says is to demonstrate that a spacecraft can be sent to service another in space.

The experiment will then demonstrate “undocking and separation of the two satellites”.

Ms Mitra says the mission will also test India’s capabilities for inter-satellite communication as during the docking and undocking, the spacecraft will have to communicate with the Earth station and also with each other so that they know each other’s position and velocity.

The spacecraft are also carrying scientific instruments and cameras which will then be deployed. Over the next two years, they will measure radiation in space and monitor natural resources on Earth.

Isro, known for economising its missions, is also using a part of the rocket that carried SpaDeX to space – which in normal circumstances would become space debris – to conduct some important experiments in orbit for three months.

Poem – short for PS4-Orbital Experiment Module – is carrying 24 payloads and has already carried out two successful experiments.

The first demonstrated seed germination. Last week, Isro tweeted a video saying that “cowpea sprouts have unveiled their first leaves in space in micro-gravity”. Micro-gravity is the near-weightless condition experienced aboard spacecraft.

Scientists say it’s great news as it means that future astronauts could produce food during long-duration missions.

The second experiment involves the robotic arm which, Ms Mitra says, is among the rocket’s most important payloads. A video on Isro’s X account shows the robotic arm moving to grab a piece of space debris.

Ms Mitra says this arm will play “a crucial role during the building of the space station as it could be used to capture and put things in place”. It will also come in handy in Chandrayaan-4 – India’s next mission to the Moon which will aim to collect and bring back lunar soil samples, she adds.

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