Building cities on Mars has long been a symbol of human ambition, but the practical reality behind it is more complicated than the dream. A recent preprint study led by Serena Suriano explores one of the biggest hidden challenges: where exactly construction materials will come from. Mars has iron, but lacks many of the special elements needed for advanced manufacturing, such as boron and molybdenum. Without these, building sustainable infrastructure becomes extremely difficult. Because of this limitation, researchers are increasingly looking beyond Mars and turning their attention to the main belt asteroids as a potential supply source.
Why Mars Looks Rich in Resources But Actually Isn’t
Mars often appears rich in resources when viewed from a distance, but its geological history tells a different story. Unlike Earth, it did not experience long-term tectonic activity capable of concentrating valuable minerals into accessible deposits. As a result, most of its metals are widely scattered rather than available in concentrated ore veins.Iron is abundant and gives the planet its distinctive red appearance. However, iron alone is not enough to create a functioning industrial base. Advanced manufacturing requires a variety of alloying elements that are either rare or extremely difficult to extract on Mars. Experts suggest that although early settlements may have depended on local resources for basic survival, large-scale development would quickly lead to material shortages.This creates a fundamental bottleneck. A Mars colony may be able to sustain life, but not necessarily expand into a full-fledged city without importing materials from elsewhere, according to the study published under Cornell University, titled, ‘Asteroid Mining to Sustain a Mars Colony: A Logistics Point of View’.
How the asteroid belt could become a resource hub for Mars missions
To address this gap, the study proposes a bold idea: use main belt asteroids as a source of industrial materials. These asteroids, located between Mars and Jupiter, contain both metal- and volatile-rich bodies. Metallic asteroids can provide iron and nickel, while carbon-rich asteroids contain water and compounds that can be used to produce fuel.At first glance, this approach seems to work. In practice, this depends largely on orbital mechanics, making the process far more complex than flying to a nearby space rock and returning with cargo. Each journey requires careful alignment between planetary position, fuel availability, and spacecraft capability.Researchers have reportedly identified a small number of asteroid pairs that could work within a realistic energy range. Nevertheless, the system would operate on a much longer time scale, with each supply cycle taking years rather than months.
How a spacecraft like Starship could handle asteroid mining missions
The study models its logistics around a spacecraft similar in capability to SpaceX’s Starship. This theoretical vehicle has large payload capacity but is still constrained by the rules of rocketry. Most of its mass is devoted to fuel rather than cargo, a limitation driven by the famous rocket equation.Fully fueled, such a spacecraft could achieve a delta-v of about 6.4 km/s. This is significant, but not sufficient to accomplish a full mining and return mission in a single trip into the asteroid belt. Most viable routes require significantly more energy, often more energy than a single fuel load can support.Because of this, the study suggests a multi-stop system. The spacecraft will first visit a metallic asteroid to collect material. It will then move towards another asteroid rich in water and hydrocarbons, where it will be able to refuel by producing propellant in space. Only after this second stop will it return to the orbit of Mars with its cargo.
The slow reality of space fuel production
One of the most challenging aspects of this system is in-situ propellant production or ISPP. The process involves extracting water from asteroids and converting it into usable fuel. While the concept is well understood, the practical rate of production is extremely slow. Some estimates suggest a production rate of only a few kilograms per day under current assumptions. At that speed, refueling a large spacecraft could take years. In extreme cases, a full refueling cycle could stretch for centuries if no improvements were made.This creates a major bottleneck in the system. Even if the spacecraft and asteroid route were viable, the refueling process alone could dominate the mission’s timeline.
Why might asteroid mining take decades, not years?
Despite the difficulties, the study does not refute the idea. Instead, it makes asteroid mining physically possible but heavily constrained by time, energy, and current technology levels. Over a long enough time frame, a single spacecraft operating continuously could deliver significant amounts of material to Mars, possibly around a few hundred tons, for decades.There is also the possibility that future propulsion systems, such as solar electric engines or solar sails, could improve efficiency and reduce travel times. However, experts caution that these technologies are still developing and may not be ready for large-scale interplanetary logistics in the near future.The vision that emerges in the end is not one of rapid expansion, but of slow accumulation. If a Martian city ever becomes a reality, it may rely less on dramatic breakthroughs and more on stable, patient supply chains spanning the solar system.