University Team Proposes Retractable, Pressurized Tunnels for Mars Missions

NASA and China’s national space agency have established long-term plans to send humans to Mars within the coming decades. According to NASA’s "Moon to Mars" mission strategy, these crewed expeditions will depend heavily on infrastructure developed during the Artemis Program. The objective is to dispatch crews to the Red Planet sometime in the 2030s or 2040s. Similar to the Artemis missions, these ambitious efforts aim to establish permanent habitats. These structures will provide critical support for long-term exploration and extensive scientific research on the Martian surface.

However, transporting humans to Mars presents formidable difficulties. The journey through deep space is prolonged, exposing astronauts to microgravity, which can cause significant physiological harm. Upon arrival on Mars, the challenges persist. The Martian atmosphere is too thin to support human respiration. Temperature fluctuations are extreme, shifting from frigid cold to surprisingly warm conditions. Furthermore, the surface is exposed to high levels of cosmic radiation. These dangers necessitate innovative solutions from space agencies and their research partners.

In a recent technical report, the Bioastronautics and Life Support Systems (BLiSS) team at the University of Michigan proposed a sophisticated solution. They designed an active, pressurized tunnel system intended to connect various habitats on the Martian surface. This system would allow astronauts to move safely between locations without stepping outside into the harsh environment. By creating a protected corridor, the team aims to mitigate the risks associated with surface travel.

The team’s concept is detailed in a paper titled "LATCH: Lightweight Actuated Tunnels for Crewed Habitation." They submitted this report to the annual Moon to Mars eXploration Systems and Habitation (M2M X-Hab 2026) Academic Innovation Challenge. NASA selected this report as one of several projects under the X-Hab program. This program is administered by the National Space Grant Foundation (NSGF). It invites university students across the United States to share concepts, prototypes, and lessons that could shape future space missions.

Dr. Nilton Renn leads the BLiSS team as the Principal Investigator. He holds the position of John R. Barker Collegiate Professor in Planetary Sciences and Space Engineering at the University of Michigan. Dr. Tracie Prater from NASA’s Marshall Space Flight Center served as the Project Sponsor. She is also a materials engineer at United Launch Alliance. Together, they guided the development of this innovative transit system, ensuring that the design met rigorous technical standards.

Regardless of whether astronauts are on the Moon or Mars, maintaining a continuous human presence requires extensive movement. Crews must travel from the surface to orbit and between different assets, such as habitats, vehicles, and landing pads. The environments on both celestial bodies are so hostile that crew members must wear spacesuits for every trip. They must conduct Extravehicular Activities (EVAs) for all surface work.

This process is slow and dangerous. It takes a full day to complete the necessary preparations. Astronauts must pre-breathe pure oxygen to prevent decompression sickness, a condition caused by rapid pressure changes. They then spend hours suiting up, depressurizing the airlock, and performing their tasks. Afterward, they must undergo a cleanup process. This routine places crew members at risk of exposure to dangerous radiation and sudden changes in air pressure.

The situation becomes even more complex when astronauts need to enter or leave the Mars Ascent Vehicle (MAV). They must remain in their bulky spacesuits during both launch and landing. This adds significant weight to the spacecraft. The suits take up valuable space, roughly the volume of a human body. This requires a larger cabin, which in turn demands more fuel for lift-off. As the BLiSS team noted in their report, each EVA suit requires 560 kilograms more propellant than a lighter Intra-Vehicular Activity (IVA) suit would need. More propellant means higher costs and greater operational complexity.

To address these problems, the BLiSS team proposed a lightweight, pressurized tunnel system. This system would provide active positioning and berthing between crewed surface assets on Mars. The tunnels could be deployed only when needed for travel. When not in use, they would retract into a compact form. This design would reduce transit times between habitats and landing pads from a full day to just a few minutes.

Each tunnel consists of several key components. It features an inflatable shell, structural rings, and a passive extension mechanism driven by motors and actuators. There are also extendable handrails, tracks, and tread units mounted to each section. The tunnels connect directly to the airlocks on the habitats. The crew can extend the tunnels using a User Interface (UI).

The process begins when a crew member selects a destination, such as the MAV or another surface element. They then instruct the UI to extend the tunnel toward the hatch. The passive extension mechanism allows for fine adjustments to the path. Sensors monitor the tunnel for leaks, contamination, or faults. Ground controllers review this data to ensure proper alignment and trajectory.

Once the tunnel is fully extended and secured at both ends, it slowly fills with oxygen and nitrogen gas. When the environment is confirmed safe by sensors and ground control, the tunnel becomes a walkway. Up to two crew members can walk through it while carrying cargo. During the transit, the UI alerts other crew members if any safety issues arise. In an emergency, alert systems activate automatically. Lights, handrails, and other support systems help ensure the crew reaches the other side safely.

When the travel is complete, the tunnels depressurize and retract. This prevents radiation from building up inside and keeps Martian dust from accumulating on the outside. Keeping the tunnels retracted also makes them less vulnerable to damage from debris.

As part of their proposal, the BLiSS team created full Computer-Assisted Design (CAD) models. They also built a prototype demonstrator of the tunnel and its actuation system, along with the control software. They developed a comprehensive risk matrix to identify potential hazards. This allowed the team to assess technical, schedule, cost, and safety-related risks.

One major risk was the structure collapsing while astronauts were inside. To prevent injury or death, the team proposed adding extra floor beams or a roll-out floor. This would support increased loads, such as dropped cargo. They also addressed the risk of inaccurate docking, which could make the system unusable. They used a multi-sensor fusion approach with LiDAR and computer vision. This allowed for cross-validation between sensors, enabling course corrections and precise movements.

"By implementing robust mitigation measures and continuously monitoring and reassessing risks throughout the project life cycle, we aim to minimize disruptions and maximize the effectiveness of our tunnel system," the team stated.

Another team from Baldwin Wallace University also submitted a similar concept called T.R.E.A.D. (Tunnel Ready Elements for Active Deployment). Their design also focused on extending tunnels to connect surface elements on Mars. They emphasized reusability and preventing clutter on the surface. Their concept used a double-tendon-based actuation system with pressurized bladders. Each set of tendons had four cables controlled by a winch. The first set controlled the initial curve, and the second controlled the final stretch. This system allowed the tunnel to bend and adjust to uneven terrain.

These proposals are just some of the latest ideas for how astronauts will live and work on Mars. As the 2030s approach, NASA and other agencies are ramping up preparations for crewed missions. The methods used and the lessons learned from these early missions will likely inform the blueprint for off-world living. These efforts may help humanity take its first steps toward becoming an interplanetary species.