A robot designed and built at the US’s Caltech has assembled part of a structure in space on its own, without astronauts, the first time this has been done. The robot, called ASTRA, has spent the past 6 months in orbit building sections of a frame for a 1.4-metre reflector antenna.

"This is the first time that a structure has been autonomously constructed in space," said Sergio Pellegrino, the Caltech aerospace professor who leads the team. The project is funded by DARPA, the US military's research agency, under a programme called NOM4D.

ASTRA works a bit like a robotic arm putting together a construction toy. It picks up carbon fibre tubes and aluminium joints from dispensers, fits them into identical sections called bays, attaches a light, net-like reflective film, then pushes each finished bay out and starts the next.

The payload, about 1 cubic metre in size, launched on 30 March 2026 on a SpaceX rocket, carrying 2 prebuilt bays and the parts for the rest. In orbit, it built a third bay. The full frame needs 11 bays, and with the mission ending in December, the team says it is unlikely to finish, after running into time limits and many small problems.

Fixing them was slow. The team can only talk to the robot during 7 or 8 windows of about 15 minutes a day, so they kept an identical twin in their lab, recreated each problem on it, found a fix, and then sent the fix up to orbit. The space payload was designed, tested and delivered in under 12 months.

Caltech's announcement says the demonstration shows the assembly method works and can be scaled up to much larger structures. "By 'very large,' I mean hundreds of meters or kilometres in scale. Nothing approaching that scale can be achieved today," said Andrew Detor, who runs the NOM4D programme at DARPA.

Today, anything sent to space has to fit inside a rocket, either folded up and opened in orbit or assembled by astronauts over several launches. That puts a hard limit on how big space telescopes, antennas and solar arrays can be. Building them in orbit, from parts launched separately, removes that limit, and ASTRA is the first proof that a robot can do it alone.

It’s an early step: one section built, not a finished antenna. But Pellegrino points to uses well beyond astronomy, including communications and very large solar arrays to collect power in space, the same kind of large orbital structures behind ideas like Google's space data centres. Cheaper launches, as Starship reaching orbit promises, and robots that can build once they get there, are 2 halves of the same future.

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