If we want big things in space, we’ll have to build and assemble them there. Rocket fairings are not large enough to accommodate the large things we want to have in space. Not only that, but the stubborn rocket equation refuses to bend itself to our desires.
Telescopes like the JWST feature ingenious folding designs that unfold in space like insects metamorphosizing. That was a very impressive way to bypass the restrictions imposed by rocket fairings. But that’s not practical in every case.
What’s far more feasible is sending smaller components into space inside fairings and then assembling them into a larger structure once there. That’s what NOM4D,
the Novel Orbital and Moon Manufacturing, Materials and Mass-efficient Design program is demonstrating. NOM4D reached an important milestone recently when it successfully demonstrated automated in-space assembly for the first time.
The demonstration involved a gantry robot, also known as a linear robot, building a typical truss structure. Gantry robots move in straight lines along x, y, and z axes. The payload came from Caltech and consisted of individual components with custom joints put together to form the structure. The individual components were not only assembled, but a thin reflective mesh that mimics what a space-based antenna might have was also simultaneously applied.
“NOM4D’s objective is to enable efficient, scalable construction of very large structures in space,” said Andrew Detor, NOM4D program manager. “By ‘very large,’ I mean hundreds of meters or kilometers in scale. Nothing approaching that scale can be achieved today.”
This concept image shows a space-based antenna autonomously assembled by a NOM4D-type device. Image Credit: DARPA | Colie Wertz
There is no shortage of ideas of how space-based manufacturing and construction could be used, but it all starts with programs like NOM4D. NOM4D is fairly simple at this point, like a child’s construction toy, but that’s its strength.
“You can think of the Caltech approach as similar to Tinkertoys or K’nex construction toys: individual truss members are joined at nodes, one section at a time, to create a larger structure,” Detor said. “Within the automated assembly box, each section is built piece by piece, a reflective mesh is attached, and the assembled sections are deployed as they are complete. There are no complicated robotics or advanced algorithms; it’s just solid engineering from the Caltech team to combine operations in a way that scales.”
Decades ago, thinkers proposed different types of rotating space stations that could be homes for thousands of people. The O’Neill Cylinder is probably the most well-known one of these, and space-heads and sci-fi dreamers of a certain age may have carried around a dog-eared copy of Gerard K. O’Neill’s “The High Frontier: Human Colonies in Space.”
“More important than material issues, I think there is reason to hope that the opening of a new, high frontier will challenge the best that is in us, that the new lands waiting to be built in space will give us new freedom to search for better governments, social systems, and ways of life, and that our children may thereby find a world richer in opportunity by our efforts during the decades ahead,” O’Neill wrote.
The O’Neill Cylinder lies in the realm of science fiction or the distant future for now, as do O’Neill’s hopes for humanity. But that was 50 years ago, and technology has advanced considerably, even if how humans conduct themselves hasn’t advanced at the same pace.
But there are other proposed space structures that are closer to reality, and they may be stages towards O’Neill’s hopeful vision that can be built by NOM4D or its successor.
It may begin with Low-Earth Orbit transfer stations and lunar orbit stations that would expand our presence in space. The proposed Lunar Gateway was one of these, and was envisioned as a modular design built in space from pre-made components. It would be a docking station and communications relay facility for trips to the lunar surface and operations there. These types of orbital facilities could be hybrids of pre-made components and structural frameworks made by NOM4D or something like it.
This concept image shows how a NOM4D-inspired device might autonomously construct a circular truss structure in space. Image Credit: DARPA | Colie Wertz
Another future use for scalable construction concerns lunar lava tubes. The Moon has what appear to be networks of subsurface lava tubes that provide natural protection from hazards. Robotic assembly could feasibly be used to reinforce these natural tubes and turn them into habitats.
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Another idea is liquid mirror telescopes. Building a huge telescope mirror and sending it into space would be near impossible, but a liquid mirror telescope could be built in a lunar crater out of components shipped individually into space. And NASA’s Lunar Crater Radio Telescope (LCRT) is a concept for a crater-based telescope on the lunar far side, isolated from Earth’s radio pollution. These ideas are waiting for the engineering to catch up.
“In a future space economy, we’re going to need large things,” Detor said. “Think large space depots or habitats, large solar arrays to collect power, or large radio antennas to explore the edges of the universe. Those things require size, and NOM4D gives us a path to accelerate creation of new capabilities.”
The rapid advancement of the NOM4D program surprised even NOM4D personnel themselves. This successful on-orbit demonstration wasn’t expected to happen so soon.
Back in February 2025, NOM4D changed its timeline. What was expected to be a third phase of more laboratory tests was instead changed to on-orbit tests, and SpaceX launched Caltech’s NOM4D payload into space in March 2026.
“Caltech [California Institute of Technology] and the University of Illinois Urbana-Champaign have demonstrated tremendous advances in the first two phases and have now partnered in Phase 3 with space-launch companies to conduct in-space testing of their novel assembly processes and materials,” Detor said at the time. “Originally, Phase 3 was going to be about making things more precisely in the lab than we did in Phase 2. But we said, ‘You know, the maturity is there, and there would be more impact if we took the capabilities we have now and actually go demonstrate them in space to show that it can be done,’”Detor said.
Now, way ahead of its original schedule, NOM4D has demonstrated its capabilities and is maturing rapidly. As Detor makes clear, leaping from the laboratory to space is a huge jump.
“It’s the speed and the scale that made this a DARPA project. We went from the idea of an on-orbit demo to launching a working prototype into space in 15 months,” Detor said. “Operating in space is much harder than operating on the ground – there’s virtually no margin to address issues that may arise. Testing in the operational environment is instrumental to rapidly maturing the technology.”
There’s still another test upcoming for NOM4D now that it’s demonstrated successful on-orbit assembly. Next, the NOM4D team from University of Illinois Urbana-Champagne will launch a test project to the ISS. This will be more than just assembly; it will demonstrate composite material processing. A monomer resin will be used to build a high-strength structure in space. It will use an energy-efficient method to heat the resin and create a strong polymer. This is similar to how resins are used in Carbon Fiber Reinforced Polymer (CFRP) manufacturing to build things like aerospace components, where strength and light weight are critical.
If that test is successful, then it really will be time to start thinking big, according to Detor.
This concept image shows what the future of NOM4D-like construction might look like. Large space structures like these could be built entirely in space. Image Credit: DARPA | Colie Wertz
“The NOM4D Caltech demonstration is not an endpoint; it’s a beginning,” Detor said. “Now that we’ve demonstrated a process that can scale to large structures, what do we go make? What wild ideas get assembled thousands of miles above us and what new capabilities do those structures enable?”
Is it time to open Gerard K. O’Neill’s seminal book again?
The O’Neill Cylinder, the OG of space habitats. Maybe one day. Image Credit: By NASA/Rick Guidice – https://space.nss.org/settlement/nasa/70sArtHiRes/70sArt/art.html (image link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=675434
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Source: Universe Today
