The robotic system was developed by researchers at the California Institute of Technology (Caltech) with funding from the Defense Advanced Research Projects Agency (DARPA). It is part of DARPA's Novel Orbital and Moon Manufacturing, Materials, and Mass-efficient Design (NOM4D) program, an initiative exploring ways to manufacture and assemble enormous structures directly in space.

Rather than relying on astronauts to connect individual pieces, the robot uses an automated arm to retrieve structural tubes and connecting joints from nearby storage dispensers. It then joins the components into repeating sections, called bays, that form a larger supporting framework known as a truss.

"This is the first time that a structure has been autonomously constructed in space," says Sergio Pellegrino, the Joyce and Krent Kresa Professor of Aerospace and Civil Engineering, the Lynn Booth and Kent Kresa Department of Aerospace Leadership Chair, the executive officer for aerospace, and a senior research scientist at JPL, which Caltech manages for NASA.

A Historic Step Toward Building Giant Structures in Space

Pellegrino leads Caltech's Autonomous In-Space Tensioned Reflector Assembly (ASTRA) demonstration. The robotic system has spent six months in orbit attempting to construct a reflector antenna measuring 1.4 meters across. Its design combines composite fiber tubes, aluminum connectors, and a lightweight reflective surface made from Kapton, a durable polymer film commonly used in spacecraft.

DARPA compares the assembly process to building with sophisticated versions of K'Nex or Tinkertoy construction toys. However, making a robot perform those same tasks reliably in the harsh environment of space presents a far greater engineering challenge.

The team encountered technical difficulties and scheduling constraints that prevented it from finishing the entire antenna. Nevertheless, the robot successfully assembled an initial section, providing evidence that this construction method can work in orbit. Researchers believe the same basic approach could eventually support much larger frameworks carrying enormous reflective surfaces.

The orbital experiment represents the third stage of DARPA's research program. During the first two stages, Caltech researchers developed the construction concept, worked out the engineering design, and verified its operation in laboratory experiments on Earth. The team then had less than 12 months to manufacture, test, and deliver the space hardware to Momentus Inc., the company hosting the payload.

"Developing a payload of this complexity on such a short timeline was an enormous undertaking for our small team," says Pellegrino, who is also co-director of the Space Solar Power Project, which aims to harvest solar power in space and wirelessly transmit it to Earth's surface. "As we wrap up the mission, we are finally able to start thinking about the new avenues of research opened by this demonstration."

Why Scientists Want to Build Enormous Structures in Orbit

The ability to assemble large structures directly in space could transform astronomy, communications, and space based energy systems.

For example, future telescopes could use enormous reflective surfaces to collect more light and observe extremely distant objects. Similar structures could also support powerful radio antennas, allowing scientists and engineers to build communications systems much larger than those that can currently be launched.

One of the greatest obstacles is the limited room available inside a rocket's fairing, the protective enclosure that surrounds its payload during launch. No matter how ambitious a spacecraft design might be, its components must somehow fit inside that confined space.

Traditionally, engineers have addressed this problem in two ways. They either fold large structures into compact packages that can unfold after reaching orbit, or they launch separate components and have astronauts assemble them in space. Both approaches impose practical limits on the size and complexity of the finished structure.

Robotic construction offers a third possibility. Instead of fitting an enormous telescope or antenna inside a rocket, engineers could transport its materials into orbit and assemble the complete system there.

DARPA's Plan for Kilometer-Scale Space Structures

DARPA established NOM4D in 2022 to investigate technologies that could eventually "ferry raw materials from Earth for in-orbit manufacturing," according to the program's website.

Caltech's ASTRA experiment is one of only two projects selected to advance to the program's third phase, which involves demonstrating construction technologies in orbit.

The other project, led by the University of Illinois Urbana-Champaign, will use a module attached to the International Space Station to investigate a technique for hardening carbon tubes in space. This could provide another way to manufacture structural components without having to complete every step on Earth.

"NOM4D's objective is to enable efficient, scalable construction of very large structures in space," said Andrew Detor, DARPA program 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."

Such structures could eventually be several football fields long or even extend for kilometers, far beyond the dimensions of conventional spacecraft.

How Caltech's Construction Robot Reached Space

ASTRA began its journey on March 30, 2026, when a SpaceX Transporter-16 mission launched from Vandenberg Space Force Base in California early that morning.

The robot traveled aboard Momentus Inc.'s Vigoride 7 orbital vehicle, which carried 10 separate payloads into low Earth orbit. ASTRA occupied approximately one cubic meter of space, a compact package containing both the assembly machinery and the materials required for construction.

Inside were two previously assembled truss bays, reinforced with diagonal tubes and connecting joints. The payload also included a robotic arm and motorized dispensers loaded with the parts needed to construct the remaining sections.

The successful launch was an emotional moment for the small engineering team watching from Earth. Jaden Suh, a former Caltech postdoctoral scholar who is now an assistant professor at the University of Texas at Austin, was moved to tears as the spacecraft carrying his team's work headed into orbit.

"As a child, I was super curious about and interested in space structures. Just like many other engineers working in this field, sending your stuff to space is what I've been dreaming of my entire life," Suh says. "I was extremely lucky to have the opportunity to work on this project, beginning from scratch. A lot of my original ideas are included in this system, and it was just incredible seeing it reach space."

Building a Structure Hundreds of Miles Above Earth

After ASTRA reached orbit, researchers began operating the system by transmitting instructions to its onboard computer through the Vigoride spacecraft.

The initial steps involved releasing the mechanisms that had secured the components during launch. The robot then extended the two previously assembled truss bays out of the machine and proceeded to construct a third bay using the onboard assembly system.

Three team members managed the construction commands from Earth: Charles Sommer, a former Caltech systems engineer; Alan Truong, a Caltech research engineer; and graduate student Tara Venkatadri (MS '24).

Although the robot carried out the assembly operations automatically, the researchers monitored its progress using photographs transmitted from orbit. When something went wrong, they examined the images, adjusted their instructions, and attempted the operation again.

These setbacks were an important part of learning whether the technology could function outside a controlled laboratory.

"That's basically the reason you do proof-of-concept testing. There are a lot of differences in the space environment compared to down on Earth," Suh explains. "There are always lots of little surprises."

Solving Unexpected Problems From Earth

To diagnose problems in orbit, the engineers relied on a second ASTRA system kept at Pellegrino's laboratory at Caltech. This backup unit, known as a flight spare, allowed researchers to recreate difficulties encountered by the spaceborne robot and experiment with possible solutions.

"Every time we confirm there is an issue in space, we come to the laboratory and try to mimic the problem on the ground," Sommer says.

Communication restrictions made troubleshooting especially challenging. The team could contact ASTRA only during approximately seven or eight brief periods each day, with each opportunity lasting about 15 minutes.

That meant engineers had to make the most of their limited communication windows. They used the laboratory twin to investigate problems, evaluate different solutions, and determine which adjustments were most likely to work. Once a solution was ready, they sent the revised instructions to the robot in orbit.

This process helped the team work through numerous unexpected difficulties while gathering valuable information about what future autonomous construction systems will need to operate more reliably.

How the Robot Assembles a Space Antenna

ASTRA's intended construction process involves repeating a carefully coordinated series of movements.

First, the robotic arm retrieves structural components from their storage dispensers. It positions the tubes and joints on an assembly plate and connects them to create a new truss bay.

Once the framework is assembled, the robot is designed to attach a thin reflective film containing many tiny openings. This material forms two reflective cable nets that are held under tension against one another by springs, helping the resulting surface maintain its intended shape.

The special film was jointly invented by researchers at Caltech and the University of Pennsylvania, where the collaborating team was led by Professor Igor Bargatin.

Unlike the knitted metallic mesh typically used in reflectors designed to fold and unfold, the perforated film requires less tension to maintain its shape. That allows engineers to reduce the amount of supporting structure needed, potentially making the entire assembly substantially lighter.

Lower weight is especially valuable in space engineering because every additional kilogram increases the demands placed on a launch vehicle.

When a bay is finished and its reflective components have been prepared, the robotic system pushes the completed section outward into space. It then begins assembling the next bay.

The full ASTRA antenna design calls for 11 connected bays, each attached to the reflective nets and extended outward from the assembly system.

A Small Demonstration With Enormous Implications

Despite successfully demonstrating the construction technique, the researchers do not expect ASTRA to finish assembling all 11 bays before the mission concludes in December.

The experiment has revealed several ways the robotic hardware and assembly procedure could be simplified and improved. Even without a completed antenna, the team believes it has collected enough evidence to establish that the approach is technically feasible.

The implications extend well beyond the relatively small antenna used in this demonstration.

Future robotic construction systems could help scientists build gigantic space telescopes that collect more light, radio antennas capable of supporting advanced communications, and enormous solar arrays designed to capture sunlight in orbit.

Such solar power systems could potentially transmit collected energy wirelessly to receivers on Earth, an idea being explored through Caltech's Space Solar Power Project.

More broadly, the successful test suggests that the size of future space infrastructure may not always have to be dictated by the dimensions of the rockets used to launch its components.

"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 says. "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."