Caltech robot builds a structure in orbit without astronauts, in an apparent first

A robotic arm designed and built at the California Institute of Technology has autonomously assembled a section of a truss structure in low Earth orbit, without any assistance from astronauts, in what the university describes as the first demonstration of its kind. The milestone, confirmed in a Nov. 6 Caltech news release and reported the same day by Phys.org, caps roughly seven months of on-orbit operations for a payload called ASTRA, short for Autonomous In-Space Tensioned Reflector Assembly.

ASTRA launched March 30 from Vandenberg Space Force Base in California, one of ten payloads riding on Momentus Inc.'s Vigoride 7 orbital service vehicle aboard a SpaceX Falcon 9 Transporter-16 rideshare mission, according to Caltech. The roughly 1-cubic-meter payload carried two prebuilt truss sections, known as bays, along with a motorized manipulator, dispensers of struts and joints, and 11 cameras. In orbit, the system went on to build a third bay on its own, assembling composite fiber tubes and aluminum joints into a section of what is meant to become a 1.4-meter-diameter reflector antenna faced with a perforated Kapton film. Caltech says the full design calls for 11 bays, and with the mission scheduled to end in December, the team does not expect to finish the complete structure before time runs out.

Commanding a robot from the ground, in short bursts

Engineers working with Sergio Pellegrino, a Caltech professor of aerospace and civil engineering who also holds a senior research scientist appointment at NASA's Jet Propulsion Laboratory, controlled the hardware remotely, limited to roughly seven or eight communication windows a day, each lasting about 15 minutes, as Vigoride passed within range of ground stations. Team members named in the Caltech release, including research engineer Alan Truong and graduate student Tara Venkatadri, said they often had to diagnose anomalies using a flight spare of the hardware kept in Pellegrino's campus laboratory, reproducing a problem on the ground before sending a fix up to the orbiting unit. Jaden Suh, a former Caltech postdoctoral researcher now on the faculty at the University of Texas at Austin, is quoted in the release saying the team encountered frequent small surprises attributable to differences between conditions on Earth and in space. Caltech says the concept and underlying design method were developed and tested on the ground in two earlier phases of the project, and that the flight payload itself was completed, tested and delivered to Momentus for integration in under 12 months.

A workaround for the limits of rocket fairings

The project is funded through the Defense Advanced Research Projects Agency's Novel Orbital and Moon Manufacturing, Materials and Mass-efficient Design program, known as NOM4D, which DARPA established in 2022 to get around a basic constraint on spacecraft: nearly everything launched today must be compact enough to survive being folded or packed inside a rocket's nose cone. According to DARPA's program materials, engineers have generally had three options for building anything larger than a fairing allows: fold a structure and unfurl it in orbit, launch it in pre-finished sections for later connection, or fabricate it from raw materials once it is already in space. ASTRA tests that third approach. It is one of two Phase 3 demonstrations DARPA moved out of the laboratory and into orbital conditions; the other, led by the University of Illinois Urbana-Champaign, uses the International Space Station's Bishop Airlock module to test a process for hardening carbon-fiber tubes in space, rather than a free-flying robot.

"This is the first time that a structure has been autonomously constructed in space," said Sergio Pellegrino, the Caltech professor who leads the ASTRA team. "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."

Caltech researchers describe ASTRA's reflective surface, a lightweight perforated film co-developed with Igor Bargatin, a mechanical engineering professor at the University of Pennsylvania, as needing less tension to stay flat than the knitted metal mesh typically used on deployable antennas, a difference the team says could allow lighter designs for future spacecraft.

What a larger version could be used for

DARPA's program manager for NOM4D, Andrew Detor, has said the effort's eventual goal is structures "hundreds of meters or kilometers in scale," well beyond anything that can be launched pre-assembled. The agency's own description of the NOM4D program frames the underlying goal as designing structures specifically for the conditions of space, rather than, as with today's deployable hardware, structures "optimized for ground test and launch survival." Caltech researchers point to large space telescope mirrors, radio antennas and solar arrays for space-based solar power as plausible uses if the approach can be scaled up and made more reliable. A separate account of the demonstration, published by the Pasadena, California, news outlet Pasadena Now, matched the Caltech release on the payload's dimensions, launch date and the number of bays completed.

Pellegrino's team says the November milestone shows the basic approach works but that the hardware needs to be simplified before it could support an 11-bay structure or anything larger. With ASTRA's mission drawing to a close in December, Caltech says the next phase of work will focus on refining the design on the ground, informed by the specific failures encountered on orbit, rather than racing to finish assembling the test antenna before the spacecraft's operational life ends. DARPA's other Phase 3 demonstration, the Illinois carbon-tube project aboard the space station, is expected to report its own results in the coming months. Pellegrino also co-directs Caltech's Space Solar Power Project, which has separately tested lightweight deployable structures intended to beam solar energy collected in orbit back to Earth, work the university frames as a long-term motivation for finding cheaper ways to build large structures off the planet.