University Team Proposes Retractable, Pressurized Tunnels for Crewed Missions to Mars
As humanity stands on the threshold of becoming a multi-planetary species, NASA and China's National Space Administration (CNSA) are independently advancing ambitious plans to send crewed missions to Mars within the coming decades. Per NASA's Moon to Mars mission architecture, this monumental undertaking will leverage the infrastructure and experience established through the Artemis Program — including the Lunar Gateway and Artemis Base Camp — to propel crews toward the Red Planet sometime between the 2030s and 2040s. Much like the progressive lunar exploration strategy underpinning Artemis, these Mars missions are envisioned to culminate in the creation of permanent or semi-permanent surface habitats that will facilitate long-duration scientific exploration and sustained human presence.
This grand vision, however, is accompanied by an extraordinary suite of engineering and physiological challenges. Deep-space transits to Mars — lasting anywhere from six to nine months depending on orbital alignment — expose crews to prolonged microgravity, cosmic radiation, and profound psychological isolation. Upon arrival, the hazards do not diminish; they transform. Mars presents a uniquely hostile surface environment characterized by a thin, carbon dioxide-rich atmosphere (roughly 0.6% of Earth's atmospheric pressure), surface temperatures that can swing from +20°C near the equator on a summer afternoon to -125°C at the poles, and radiation levels estimated to be approximately 700 times higher than those experienced on Earth's surface, owing to the planet's lack of a global magnetic field and its tenuous atmospheric shielding.
Fortunately, these formidable challenges are catalyzing a wave of ingenious innovation from space agencies, affiliated research institutes, and academic partners worldwide. In a recent technical report submitted to NASA, the Bioastronautics and Life Support Systems (BLiSS) team at the University of Michigan has proposed a sophisticated active, pressurized tunnel system designed to safely and efficiently connect crewed habitats and surface assets on the Martian surface — potentially transforming how astronauts navigate their extraterrestrial home.
The X-Hab Challenge: Cultivating Tomorrow's Space Architects
The BLiSS team's concept is formally described in the paper "LATCH: Lightweight Actuated Tunnels for Crewed Habitation," submitted to the annual Moon to Mars eXploration Systems and Habitation (M2M X-Hab 2026) Academic Innovation Challenge. This report represents one of several groundbreaking projects NASA selected under the prestigious X-Hab program, an incentive challenge administered by the National Space Grant Foundation (NSGF).
The X-Hab program is a cornerstone of NASA's broader strategy to engage the next generation of aerospace engineers and scientists. By inviting university students nationwide to develop concepts, build prototypes, and distill lessons learned, NASA effectively leverages the intellectual energy of academia to explore solutions that might otherwise remain uninvestigated within the constraints of traditional agency workflows. The challenge embodies a collaborative philosophy: the brightest young minds, guided by experienced mentors, tackling some of the most daunting engineering problems in human history.
"The project calls for the development of concepts for a 'lightweight pressurized tunnel system' which can 'provide active positioning and berthing between crewed surface assets on Mars.'" — BLiSS Team, University of Michigan
Leading the BLiSS team as Principal Investigator is Dr. Nilton Renno, the John R. Barker Collegiate Professor in Planetary Sciences and Space Engineering at the University of Michigan — a distinguished researcher with deep expertise in planetary atmospheres and surface processes. Serving as Project Sponsor is Dr. Tracie Prater, an accomplished aerospace and mechanical engineer at NASA's Marshall Space Flight Center and a materials and processes engineer at United Launch Alliance, bringing critical real-world engineering experience to the academic endeavor.
The Challenge of Surface Mobility on Mars
To appreciate the elegance of the LATCH concept, one must first understand the profound logistical burden imposed by the current paradigm for surface operations on another world. Whether on the Moon or Mars, maintaining a continuous human presence demands constant movement — of crews, cargo, scientific instruments, and supplies — between surface assets such as habitats, pressurized rovers, landing pads, and ascent vehicles. Under existing mission architectures, virtually every transit between unpressurized surface elements requires crew members to perform a full Extravehicular Activity (EVA).
An EVA is far from a casual undertaking. The process involves a rigorous sequence of preparations designed to protect the astronaut from the lethal environment beyond the habitat walls. On Mars, this would typically include:
- Pre-breathing pure oxygen for several hours to purge nitrogen from the bloodstream and prevent decompression sickness
- Donning the EVA pressure suit, a complex, multi-layered garment that can take 45 minutes or more to put on correctly
- Airlock depressurization and environmental checks prior to egress
- Post-EVA decontamination, including the removal and careful storage of suits coated in potentially toxic Martian dust — a fine, perchlorate-rich particulate that poses serious health risks if inhaled
In total, this process consumes an entire workday — a staggering inefficiency on a mission where crew time is among the most precious resources imaginable. Furthermore, each EVA compounds exposure risks. Martian ionizing radiation, composed primarily of galactic cosmic rays (GCRs) and solar energetic particles (SEPs), represents a significant long-term cancer and neurological hazard for unshielded crew members. The psychological and physical toll of repeated suit-ups in a confined habitat environment also cannot be understated.
The economic and propulsion implications are equally striking. As the BLiSS team highlights in their report, the requirement for bulky EVA suits during ascent and descent in the Mars Ascent Vehicle (MAV) carries substantial penalties:
"Preliminary analysis of the Mars Ascent Vehicle (MAV) used by crew to get to and from the Martian surface shows that each EVA suit requires 560 kilograms more propellant than an Intra-Vehicular Activity (IVA) suit would require. Additionally, EVA suits take up volume in the launch vehicle, roughly the size of a person. This would require a larger cabin size, which in turn would require more propellant mass." — BLiSS Team, LATCH Report
In the unforgiving mathematics of rocket science, where every kilogram of additional mass on Mars must have been launched from Earth at enormous cost, a 560-kilogram propellant penalty per suit is a figure that demands serious engineering attention. This context makes the case for pressurized surface connectivity systems not merely convenient, but potentially mission-critical.
LATCH: An Elegant Engineering Solution
System Architecture and Design
The LATCH (Lightweight Actuated Tunnels for Crewed Habitation) system proposes a network of retractable, pressurized tunnels that can be deployed on demand to create safe, shirt-sleeve passageways between surface habitats, the MAV, and other crewed assets — then retracted when not in use. By replacing full EVAs with pressurized internal transits, LATCH could theoretically reduce crew movement times from a full day to just a few minutes, dramatically increasing mission productivity and crew safety.
Each individual tunnel unit is an integrated assembly of several critical components:
- Inflatable outer shell: A flexible, multi-layer pressure vessel providing structural integrity and atmospheric containment
- Structural rings: Rigid hoops distributed along the tunnel length to maintain cross-sectional shape under internal pressure and external loads
- Passive extension mechanism: A motor- and actuator-driven system enabling controlled deployment and retraction of the tunnel sections
- Extendable handrails and interior tracks: Providing crew members with stable footholds and handholds during transit, especially critical in Mars's 0.38g gravitational field
- Tread units: Mounted to each tunnel section to enable movement and positioning across the Martian surface
- Integrated sensor array: Continuous monitoring for pressure leakage, atmospheric contamination, structural faults, and environmental hazards
Operational Sequence
The operational workflow of the LATCH system has been designed with crew safety and simplicity as paramount concerns. The process is initiated through a dedicated User Interface (UI) accessible to both crew members inside the habitat and ground controllers at mission support centers on Earth. A typical transit sequence unfolds as follows:
First, the crew member selects a destination — the MAV, an adjacent habitat module, a science outpost, or another surface element — and commands the UI to begin tunnel extension. The passive extension mechanism drives the tunnel outward from its airlock interface, with the system's suite of sensors providing real-time feedback on alignment and trajectory. The crew member can make fine positional adjustments via the UI, while ground controllers monitor the operation simultaneously. Once the tunnel's distal end successfully mates with the destination hatch and both connection points are secured, the tunnel is slowly pressurized with a breathable oxygen-nitrogen gas mixture, carefully monitored to confirm a safe internal environment before crew ingress.
The tunnel is designed to accommodate the simultaneous transit of up to two crew members, potentially carrying cargo between assets. During transit, crew members remaining in the habitat are kept informed by the UI of the tunnel's status. In the event of any sudden anomaly — pressure loss, sensor fault, or structural warning — an automated emergency response protocol activates immediately: alert lighting, handrail locking systems, and additional support systems engage to guide crew members safely to either end of the tunnel.
Upon completion of transit and crew egress at the destination, the tunnel is methodically depressurized and retracted to its stowed position. This retraction strategy serves multiple protective functions: it minimizes the tunnel's exposure to accumulated ionizing radiation during periods of inactivity, reduces the deposition of abrasive Martian regolith dust on exterior surfaces, and decreases vulnerability to micrometeor and debris impacts — a non-trivial consideration given Mars's relatively sparse but still present small-body impact environment.
Testing, Prototyping, and Risk Assessment
The BLiSS team's submission went beyond conceptual description, incorporating full Computer-Assisted Design (CAD) models and a physical prototype demonstrator of the tunnel and its actuation system, complete with accompanying control software — a level of rigor that reflects the X-Hab program's emphasis on tangible deliverables. This hands-on prototyping process is invaluable, as theoretical designs frequently reveal unexpected engineering challenges only when translated into physical hardware.
Alongside the prototype, the team developed a comprehensive risk matrix to systematically identify, assess, and mitigate potential hazards across technical, schedule, cost, and safety dimensions. Among the key risks identified and addressed:
- Structural yielding under load: The risk of the tunnel floor or structural elements failing while crew members or cargo are inside. Mitigation strategies include the addition of supplementary floor beams and a deployable roll-out floor system designed to handle abnormal loads, such as dropped cargo in Mars's reduced gravity.
- Inaccurate berthing: The risk of misalignment between the tunnel's distal end and the destination hatch, which could render the pressurized connection unusable. The team proposes a sophisticated multi-sensor fusion approach combining LiDAR (Light Detection and Ranging) with computer vision algorithms, enabling cross-validation between sensor modalities for precise, real-time alignment correction and fine-motion detection.
- Pressure integrity failure: Continuous sensor monitoring and automated alert systems are designed to detect and respond to any breach of the tunnel's pressure envelope before it poses a danger to crew members.
- Dust ingestion and contamination: The retractable design inherently minimizes dust accumulation, and material selection for tunnel surfaces prioritizes resistance to the abrasive and chemically reactive nature of Martian perchlorate-rich regolith.
"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 in supporting crew transportation between surface assets during space missions." — BLiSS Team, University of Michigan
A Parallel Vision: Baldwin Wallace University's T.R.E.A.D. System
The LATCH concept is not alone in addressing this critical gap in Mars surface infrastructure. A compelling parallel proposal submitted by the Baldwin Wallace University Engineering Department introduces the Tunnel Ready Elements for Active Deployment (T.R.E.A.D.) system — another response to the 2026 M2M X-Hab Challenge's call for retractable, reusable surface tunnel solutions.
Where LATCH employs a motor-and-actuator-driven passive extension mechanism, T.R.E.A.D. takes a distinctly different mechanical approach: a double-tendon-based actuation system paired with pressurized internal bladders. The tendon system consists of two sets of cables, each comprising four individual tensioning cables controlled through a centralized winch mechanism. The first tendon set governs the curvature and trajectory of the tunnel's initial half during deployment, while the second set manages the final extension. Crucially, the tendon architecture also serves as the primary means of tunnel retraction and provides inherent terrain-following flexibility — allowing the tunnel to articulate and accommodate the uneven, boulder-strewn topography typical of Martian surface environments.
Both LATCH and T.R.E.A.D. share a common philosophical underpinning: the emphasis on reusability and surface cleanliness. A persistent concern in long-duration Mars base planning is the gradual accumulation of decommissioned structures, defunct tunnels, and obsolete hardware — a kind of surface clutter that complicates future operations, increases contamination risks, and may impede landing zone accessibility. By designing tunnels that retract when not in use and can be redeployed as mission needs evolve, both concepts actively counteract this entropic tendency.
Broader Implications for Mars Architecture and Interplanetary Living
The LATCH and T.R.E.A.D. concepts exist within a rich and rapidly evolving ecosystem of Mars surface architecture proposals. The European Space Agency (ESA) has explored in-situ resource utilization (ISRU) for constructing radiation-shielded underground habitats. NASA's own Human Research Program continues to investigate the physi
