Caltech Robot Builds First Structure in Space Without Astronauts
A robot built by researchers at the California Institute of Technology has assembled part of a structure in orbit with no help from astronauts, in what Caltech and the US Defense Advanced Research Projects Agency (DARPA) say is the first autonomous construction of a structure in space.
The machine, called ASTRA — short for Autonomous In-Space Tensioned Reflector Assembly — spent the past six months in low Earth orbit building a section of a 1.4-metre reflector antenna from composite fibre tubes, aluminium joints and a Kapton reflective surface. Caltech and DARPA announced the result on 5 November, and it was reported by Phys.org on 6 November. “This is the first time that a structure has been autonomously constructed in space,” said Sergio Pellegrino, the Caltech aerospace professor who leads the ASTRA team.
A third bay, built by a robot
ASTRA flew to orbit carrying two sections — known as bays — of the truss already built on Earth. Once in space, the robot’s manipulator picked struts and joints from motorised dispensers, joined them together and assembled a third bay on its own, before pushing the finished section out into space.
The full reflector was designed to have 11 bays. With ASTRA’s mission due to end in December, the team says it is unlikely to complete the whole truss. But the researchers say they have learned enough to show that the on-orbit assembly approach is viable, and that the design now needs to be simplified and refined.
There is an important limit to what was achieved. ASTRA did not build a working antenna. The demonstration used a surrogate mesh rather than the electronics a radio antenna needs, so it proves the construction method, not a working communications system.
Why building in orbit matters
The size of any structure sent to space is currently limited by the size of the rocket fairing that carries it. Until now there have been two ways to get a large structure into orbit: fold it up for launch and unfurl it in space, or piece it together by hand over a series of launches. Neither route can deliver the very large structures scientists want, so a third option is needed — building them where they will be used.
That is the aim of DARPA’s NOM4D programme, which began in 2022 with the goal of eventually ferrying raw materials from Earth for manufacturing in orbit. “NOM4D’s objective is to enable efficient, scalable construction of very large structures in space,” said Andrew Detor, DARPA’s programme manager for NOM4D, in a written statement. “By ‘very large,’ I mean hundreds of meters or kilometers in scale. Nothing approaching that scale can be achieved today.”
Six months in orbit, 15 minutes at a time
ASTRA reached orbit early in the morning on 30 March 2026, launching from Vandenberg Space Force Base in California as one of 10 payloads aboard Momentus Inc.’s Vigoride 7 orbital vehicle, which flew on the SpaceX Transporter-16 mission. The payload, roughly one cubic metre in size, survived the launch and then spent about six months working in orbit.
The work was slow and painstaking. There are only about seven or eight short windows of around 15 minutes each day when researchers on the ground can communicate with the system, and the team had to overcome a series of unforeseen problems in the space environment. To troubleshoot, they used a flight spare — an identical twin of the payload kept in Pellegrino’s Caltech laboratory — testing each workaround on the ground before relaying it to the machine in orbit.
The commands to build the structure were sent by team members Charles Sommer, Alan Truong and graduate student Tara Venkatadri, with the outcomes checked against photographs downloaded from space by one of the payload’s 11 cameras. Jaden Suh, a former Caltech postdoctoral scholar on the team who is now an assistant professor at the University of Texas at Austin, said sending the team’s work to space was something he had dreamed of since childhood.
ASTRA is one of only two projects to reach the third phase of the NOM4D programme. The other, led by the University of Illinois Urbana-Champaign, will use a module attached to the International Space Station to test a method for hardening carbon tubes in space.
What comes next
If the approach can be scaled up, the payoff could be substantial. Scientists want far larger space telescopes that can observe ever more distant objects, as well as giant radio antennas, solar arrays and even structures that harvest solar power in space and beam it back to Earth. The capability also feeds into the wider American push to return astronauts to the Moon and build lasting infrastructure beyond Earth.
“Once you get to the size limit where structures cannot be prebuilt on the ground and unfolded, you have to think about how to build them in space,” Pellegrino said. “So, this work could be useful not only for astronomy and astrophysics but also for communications and other areas, such as building very large solar arrays for space solar power.”
The dish ASTRA was building will almost certainly never be finished. But the single bay it assembled on its own is the proof that a robot can now do in orbit what, until now, only astronauts or unfolding mechanisms could do — and that may change what can be built in space.
