Mycelium for Mars — Radiotrophic Fungi on the International Space Station

The Shielding Problem That Defines Mars Mission Design

Every kilogram lifted out of Earth's gravity well costs roughly one to two thousand dollars on a current commercial launch vehicle. For a crewed Mars mission, the radiation shielding mass is one of the dominant cost drivers in mission architecture. Astronauts on a six-month outbound trip, a Martian surface stay, and a six-month return are exposed to a galactic-cosmic-ray and solar-particle-event radiation environment that current expendable shielding materials handle inefficiently. Aluminium and polyethylene shield reasonably well by mass but require many tons to bring a deep-space habitat down to long-duration occupancy limits.

Living shielding, material that arrives as a small mass of dormant spores or culture, then grows itself into a thick protective layer at the destination, has been an aspirational concept in mission planning for decades. Until recently, the candidate organisms were either too slow, too fragile, or too biologically demanding to consider seriously. Then a 1991 sampling expedition inside the Chernobyl exclusion zone changed the calculation.

Cladosporium sphaerospermum and the Discovery of Radiotrophy

A black, melanin-rich fungus, Cladosporium sphaerospermum, was identified growing on the inner walls of the damaged Chernobyl Unit 4 reactor in environments where the gamma radiation dose rate was hundreds of times background. More striking, the fungus appeared to be growing toward the radiation source rather than away from it. Laboratory work led by Ekaterina Dadachova and Arturo Casadevall at Albert Einstein College of Medicine through the early 2000s established that the melanin in the fungal cell wall was performing a redox conversion analogous to photosynthesis, deriving usable metabolic energy from ionizing radiation. The behavior was named radiotrophy. The mechanism is still partially debated, but the empirical result has been replicated.

A radiotrophic shielding material is interesting for two reasons. It absorbs the energy it shields against rather than simply scattering or attenuating it, which alters the secondary-radiation profile inside the habitat. The organism is self-replicating from a small inoculum, so the shielding mass arrives at the destination as a few grams of culture and grows itself out of locally available substrate.

The 2018-2019 ISS Experiment

In late 2018, a research team led by Nils Averesch, then at Stanford, and Graham Shunk, an undergraduate co-investigator, sent a culture of Cladosporium sphaerospermum to the International Space Station on a SpaceX cargo resupply mission. The experiment, codename Space MICRA, was small by spaceflight standards. A petri dish split into two compartments, one inoculated with the fungus, one sterile, was monitored with a paired radiation detector for thirty days under ambient ISS radiation conditions.

The pre-flight prediction was that the fungal layer would measurably attenuate the radiation flux reaching the detector behind it. The post-flight data showed an attenuation of roughly two percent across a layer of less than two millimetres. The 2020 preprint extrapolated linearly, almost certainly an oversimplification, to a layer of approximately twenty-one centimetres providing the same shielding as a meter of Martian regolith. Even with a more conservative non-linear projection, the result was sufficient to justify a follow-up.

The Follow-Up Work and Hybrid Shielding Concepts

Subsequent work has moved in two directions. The first is improved shielding-fungus characterization. Spectroscopic and dosimetric studies have begun to disentangle the contribution of melanin pigment alone from the contribution of the living, metabolizing organism. Preliminary results suggest the living state matters. A kill-and-extract approach loses much of the absorption benefit, which has implications for shielding-system design and life support.

The second direction is hybrid mycotecture. Rather than relying on the fungus alone, current concept work pairs a thin radiotrophic outer layer with structural mycelium-bound regolith composites. Ecovative Design, a New York company that has commercialized terrestrial mycelium-bound packaging and insulation, has collaborated with NASA-funded teams on Mars-regolith-simulant binding studies. A NASA Innovative Advanced Concepts grant to Lynn Rothschild at Ames Research Center, the Myco-architecture Off Planet program, funded a parallel investigation into using mycelium binders to grow habitat walls from Martian regolith on the surface, with radiotrophic species potentially integrated as a top layer.

Why the Approach Is Still Speculative

The path from a thirty-day petri-dish demonstration to a deployable Mars habitat is long, and several open questions remain. The growth rate of radiotrophic fungi under reduced atmospheric pressure, low gravity, and Mars-relevant substrate composition is not well-characterized. Long-duration viability of the culture under the actual deep-space radiation environment, which is qualitatively different from low-Earth-orbit radiation, is open. The metabolic substrate requirement, the carbon and nitrogen sources the fungus needs to grow its protective layer, has to be either brought from Earth or generated from Martian resources, both of which add system complexity.

The economic case nevertheless remains compelling enough that the work continues to attract NASA grant funding. A passive shielding layer that arrives at Mars in a vial weighing less than a kilogram and grows itself into a structural element of the habitat is the kind of asymmetric mass-budget win that mission architects pay attention to.

What to Watch Next

The interesting flight opportunities in the next several years are the dedicated mycotecture experiments planned for the Artemis lunar surface program, which provides a lower-cost staging environment for testing radiation-shielding fungi in something closer to the Mars surface radiation profile than the ISS offers. A second thread is the gradual emergence of commercial mycotecture players, Ecovative, MycoWorks, Biohm, whose terrestrial production capacity makes a path from research concept to flight-ready hardware significantly cheaper than it would have been a decade ago.

A Mars habitat that grows itself out of regolith and a kilogram of culture remains, for now, a research program rather than a mission plan. The data trajectory since 2018 has narrowed the gap meaningfully.