Most spacecraft leave the ground fully built and folded into a rocket fairing, and that puts a hard ceiling on how big a telescope mirror or radio antenna can be. A small experiment in low Earth orbit has now tried the alternative: launch the parts and let a robot put them together in space. On 5 November 2026, Caltech and DARPA reported that the payload, called ASTRA, had built a section of truss in orbit. It is a modest first step for in-space assembly, but a real one.
ASTRA comes from Sergio Pellegrino’s group at Caltech and is funded through DARPA’s NOM4D programme, which studies how to make and assemble structures in orbit rather than on the ground. The payload, about one cubic metre in size, launched on 30 March 2026 on SpaceX’s Transporter-16 mission. It rode aboard Momentus’s Vigoride 7 vehicle with nine other payloads. Its goal was a reflector antenna 1.4 metres across.
The design works like flat pack furniture. Motorised dispensers hold composite tubes and aluminium joints, and a robotic manipulator, which DARPA describes as a simple gantry moving along three straight axes, picks out the parts and joins them into a bay. A perforated reflective film, co-invented with a University of Pennsylvania team, is then attached as two cable nets pulled taut against each other by springs. The finished bay is pushed out and the cycle starts again. A full antenna needs 11 bays.
Two pre-built bays went up with the robot, and it assembled a third in orbit. Pellegrino calls it “the first time that a structure has been autonomously constructed in space”. DARPA’s interest is scale: its stated aim is structures hundreds of metres or even kilometres across, built for space rather than designed to survive the shaking of a launch.
One bay is a long way from 11, though. Each stage was commanded from the ground, and the team could reach the payload only in seven or eight windows a day of roughly 15 minutes each, checking progress against photos sent down from orbit. Unexpected problems forced operations to be repeated, and fixes were rehearsed first on an identical flight spare in a Caltech lab. With the mission ending in December, the complete antenna now looks out of reach, and the team says the design needs simplifying.
None of that undoes the main result. A telescope that never has to fit inside a rocket is no longer only a drawing. For now it is a single bay of tubes and film, built slowly by a stubborn robot, circling Earth.
