Why lunar dust is not like dust
Terrestrial dust has been rounded by wind and water for millions of years. Lunar regolith has been shattered by micrometeorite impact in vacuum and never weathered, so the grains are sharp, angular and often glass. Under a microscope they look like broken bottles.
They are also electrostatically charged, by solar ultraviolet on the sunlit side and by plasma on the night side, which makes them cling to everything. Whether charged grains loft in any quantity is less settled than it was: the Lunar Atmosphere and Dust Environment Explorer (LADEE) set an upper limit of 100 grains per cubic metre for electrostatically lofted dust between 3 and 250 km altitude, and found instead a thin cloud kicked up by micrometeoroid impacts. Ten to twenty percent of the soil mass is finer than 20 micrometres, and the fraction that matters for the lung is finer still, below about 3 micrometres. NASA's permissible exposure limit for a six month mission is 0.3 mg of respirable dust per cubic metre of cabin air.
| Property | Lunar regolith | Terrestrial dust | Consequence |
|---|---|---|---|
| Grain shape | Angular, fractured glass | Rounded by weathering | Abrades seals, bearings and visors |
| Charge | Electrostatically charged | Mostly neutral | Clings, levitates, resists brushing |
| Sizebelow 20 µm | 10 to 20% by mass | Varies with source | The respirable fraction below 3 µm reaches the alveoli |
| Reactivityfreshly fractured | Highly reactive surfaces | Passivated | Suspected inflammatory response in lung tissue |
| Abrasiveness | Hard silicate minerals and glass | Softer, weathered grains | Wore through the outer suit layer on Apollo 12 in two extravehicular activities (EVAs) |
After two EVAs and about eight hours outside, the Apollo 12 suits were worn through the outer layer above the boots and into the insulation beneath, and Pete Conrad's suit, which had no leak before the first EVA, was losing 0.25 psi a minute against a 0.30 limit. Wrist locks and hose locks clogged. On Apollo 17 the cover gloves used on the core drill were worn through after two EVAs and discarded, Harrison Schmitt's visor sunshade was scratched until he could not see out in some directions, and after removing his helmet in the cabin he reported nasal and sinus stuffiness he compared to hay fever, from dust carried inside on the suits. Apollo 17 spent 75 hours on the surface. This base is planned for a decade.
The strategy: never let it inside
Every dust mitigation approach falls into one of three categories: stop it entering, remove it once it has, or tolerate it. Cleaning is expensive in crew time and never complete, and tolerance is what wore out the Apollo suits. So the architecture spends its effort almost entirely on the first category.
Suit ports
The suit port is the single most important dust decision in the design, and it happens to also solve two other problems.
It removes the dust path entirely, because the suit exterior is always outside. It removes the airlock pump down, because only the small vestibule behind the hatch is ever cycled; NASA's suit port work at Johnson Space Center puts the time before an EVA at under thirty minutes against hours through an airlock. And with the cabin held at NASA's exploration atmosphere, 8.2 psi and 34 percent oxygen, the prebreathe falls to about fifteen minutes.
| Measure | Traditional airlock | Suit port | Difference |
|---|---|---|---|
| Dust path into the habitat | Every EVA | None | The whole problem |
| Time before an EVA | Hours | Under 30 min | Two EVAs a day become possible |
| Atmosphere lost per cycle | The airlock volume, pumped or vented | Only the vestibule behind the hatch | Most of the consumable; not yet measured for this design |
| Prebreathe | Hours from a 14.7 psi cabin | About 15 min from 8.2 psi, 34% oxygen | Removes the largest EVA overhead |
| Suit stowage inside | Every suit, in the cabin | None, the suits stay docked outside | Volume and dust both stay outside |
Electrostatic mitigation
What the boundary does not catch is handled electrically. An electrodynamic dust shield (EDS) is a set of transparent electrodes on a surface, driven with out of phase high voltage waveforms that make a travelling electric field. Charged particles are walked along the surface and off the edge. It has no moving parts and costs almost nothing in mass. NASA's Kennedy Space Center exposed EDS panels on the station's Materials International Space Station Experiment (MISSE 11) from 2019, and on 2 March 2025 an EDS landed on Blue Ghost and cleared regolith from glass and thermal radiator samples on the surface, the first such demonstration on the Moon.
It is used on three things here: the solar array faces, the radiator faces, and the airlock curtain the crew pass through. On the array it is what keeps the site's own traffic from settling on the cells: the Apollo dust detector experiments found that dust, not radiation, was the main cause of degradation of their covered solar cells.
What still wears out
No mitigation is complete, so the design assumes wear and plans for replacement rather than pretending it will not happen.
Roads, and why they are a dust measure
A rover crossing unprepared regolith throws a rooster tail of fines that travels ballistically in vacuum and settles across the whole site. Every traverse contaminates everything downrange of it, including the array and the radiators.
Sintering the routes between the four work areas is usually presented as a mobility improvement. It is at least as much a contamination control measure: a vitrified surface generates almost no fines, so the dust budget of the whole site falls with every metre of road laid. This is the argument for building roads early rather than when they are convenient.
What is not yet known
The toxicity of lunar dust is bounded, not settled. NASA's 0.3 mg per cubic metre limit rests on animal studies with pulverised Apollo soil and sits at the low end of a 0.2 to 0.7 range from different methods; whether freshly fractured polar regolith, never exposed to air, behaves the same as returned samples is unknown. The size distribution at the Shackleton rim has not been measured, so the fraction below 3 micrometres that the airlock curtain has to capture is assumed from equatorial and mid latitude samples. Every service life in the chart is an estimate until the increment four particle counters report; the only measured record is Apollo's, and it ends at 75 hours. The suit port's gas loss per cycle has not been measured for this design, and the electrodynamic shield's power and its lifetime under years of ultraviolet and thermal cycling are known from a two week demonstration and a station exposure, not from a decade. Whether charged dust lofts in quantity near the terminator is now doubtful after LADEE, but the site sits at the terminator for months at a time, which no instrument has yet watched.
Increment plan
Increment 1, suit ports from the start
This is not retrofittable. The airlock is designed around suit ports or it is not, so it lands with them.
Increment 2, electrostatic curtain and vacuum station
The airlock interior fit out, and the first electrodynamic shields on the array.
Increment 3, sintered roads
The four routes between habitat, pad, plant and excavation face. This is where site wide dust generation drops sharply.
Increment 4, monitoring
Particle counters in each module and on the array, so degradation is measured rather than inferred. Nobody has ever had long duration dust data from the surface.
Sources and further reading
Every figure in this document traces to one of these. Agency documents and peer reviewed work first, reporting only where it is the primary record.