The target resource is water ice buried beneath Martian soil and rock. Orbital observations indicate that extensive deposits occur in the planet’s mid-latitudes, sometimes beneath only centimeters to meters of regolith. At some scarps, exposed ice sheets begin roughly one to two meters below the surface and extend more than 100 meters downward. Such deposits could eventually supply water for life-support systems and for producing rocket propellant. The quantities involved are substantial: previous mission studies have estimated that a Mars ascent vehicle could require about 150 metric tons of water, while refueling a Starship-class vehicle could require approximately 600 metric tons. Reaching ice is therefore not simply a matter of finding it from orbit. A practical system must penetrate uncertain mixtures of rock, sediment, dust, and ice, remove the debris continuously or in controlled pulses, and then establish a subsurface reservoir. RedWater combines a rotary-percussive drill with a later melting and pumping sequence based on Rodriguez Well, or Rodwell, technology developed for extracting water from terrestrial polar ice.

During the drilling phase, a bottom-hole assembly breaks the formation into small particles. A hollow metallic coiled tube deploys the assembly and carries electrical, pneumatic, and hydraulic lines from the surface. Gas released near the drill bit entrains the particles and pushes them upward through the annulus. RedWater uses direct circulation: gas travels down the drill string, exits at the bit, and returns through the surrounding borehole space with the cuttings. This arrangement is simpler than reverse circulation, in which debris travels up the center of the drill pipe through a more complicated flow path. The choice is important because the gas must do two jobs. It must first pick up newly created particles at the bottom, then sustain a dilute flow capable of transporting them through the full depth of the hole. If the gas speed is too low, the particles can settle, form dense regions, and recirculate rather than leave the borehole. Accumulating debris increases the energy required to drill and can ultimately cause the drill to stall.

The model treats that transition using empirical correlations for vertical pneumatic conveying. Its central quantity is the choking velocity, the approximate gas speed below which particle transport becomes inefficient. The calculation accounts for borehole geometry, gas density and viscosity, temperature, pressure, gravity, particle density, particle diameter, particle sphericity, and the rate at which the drill advances. Because the borehole is an annulus rather than a round pipe, the researchers use a hydraulic diameter equal to the borehole diameter minus the diameter of the RedWater assembly or coiled tubing. The model estimates the mass flux of cuttings from the borehole area, penetration rate, and density of the material being drilled. It then calculates particle free-fall speed from drag relationships and corrects that speed for the irregular shape of real drill chips. Voidage, the fraction of the conveying volume occupied by gas, is coupled to the choking velocity, so the equations are solved iteratively. A further iteration estimates gas density from bottom-hole pressure using the ideal gas law, including environmental pressure, gas-solid hydrostatic pressure, and frictional losses.

To connect the predicted velocity with hardware, the study converts the result into a required gas mass flow rate. That flow can be controlled using the upstream pressure, gas type, orifice area, and discharge coefficient. The researchers also apply a safety factor of 1.5 to the estimated choking velocity when defining a design condition. The approach was tested in three different settings. In a dedicated vacuum experiment, a 2.44-meter vertical annulus used a 38.1-millimeter inner tube and a 57.2-millimeter transparent outer tube. Sieved silica sand represented drill chips, while nitrogen entered at the bottom through a long supply line. The chamber pressure was maintained at 1.3 kilopascals, and a camera recorded particle motion at 30 frames per second. Steady flow tests used rates of 0.25, 0.4, and 1.0 grams per second. At 1.0 grams per second, the sand was immediately entrained and left the observed section in less than half a second. At the two lower rates, particles recirculated and some remained after the gas was shut off.

The two other experiments used the RedWater system itself. In a freezer test, the drill operated in a 1.4-meter crystalline ice tower at approximately minus 10 degrees Celsius. The system reached an average penetration rate of 0.59 millimeters per second, with instantaneous rates between about 0.35 and 0.75 millimeters per second. Nitrogen was supplied at 550 kilopascals, corresponding to a calculated flow of 16.7 grams per second, but some chips continued to recirculate. After the supply was increased to 690 kilopascals and 18.5 grams per second, the chips were observed to blow out with minimal recirculation. In a separate thermal-vacuum test, the ice was cooled to roughly 210 kelvin and the chamber pressure was reduced to 1.0 kilopascal. Carbon dioxide flowed continuously at a directly measured 0.55 grams per second, and the system cleared the brittle ice chips without visible difficulty. That test also demonstrated end-to-end operation, with liquid water delivered to a container outside the vacuum chamber, although the experiment was designed primarily as a system demonstration rather than a dedicated threshold measurement.

When measured conditions were supplied to the model, its estimates broadly matched the observed transitions. For the sand experiment, the predicted minimum was 0.97 grams per second, within the observed range between inefficient transport at 0.4 grams per second and effective clearing at 1.0 grams per second. For the thermal-vacuum experiment, the model predicted 0.45 grams per second, slightly below the 0.55 grams per second that successfully cleared the chips. The freezer prediction was 16.4 to 16.9 grams per second, close to the 16.7 grams per second at which recirculation was still visible and just below the 18.5 grams per second that cleared the borehole. Because no intermediate rates were tested, the exact threshold remains uncertain. The comparison nevertheless spans different gases, pressures, geometries, and particle conditions. The researchers report that the more than 30-fold difference between the freezer and thermal-vacuum flow rates is driven mainly by ambient pressure and its effect on gas density. At near-Martian pressure, a given gas supply can produce high velocities near the drill bit, increasing drag and momentum transfer to the particles.

The results have direct implications for mission architecture, but they do not represent a final qualification of the drilling system. The model indicates that an optimized RedWater design could require less than one kilogram of gas to drill through a meter of rocky overburden under the projected Martian conditions. Gas could be transported from Earth or compressed from the Martian atmosphere, an approach made more credible by the demonstrated operation of the MOXIE instrument’s atmospheric gas compressor. The calculations also suggest that the minimum instantaneous flow rate is not strongly controlled by the drilling penetration rate, because the gas-solid mixture remains highly dilute even as more cuttings are generated. Faster drilling can still reduce total gas consumed per meter by shortening the time the flow must operate. A pulsed system could offer another efficiency benefit: chips might be allowed to accumulate briefly before a gas pulse carries them to the surface. The pulse would need to last long enough for particles to travel the increasing distance as the borehole deepens.

Important uncertainties remain. All three experiments were performed in Earth gravity, whereas Martian gravity is about 38 percent as strong, and the model predicts that lower particle weight should reduce the required gas flow. The tests also used prepared sand or relatively homogeneous ice, not fractured, porous, dusty, or mixed Martian formations. Gas could leak into surrounding rock or ice instead of returning through the annulus, raising the supply requirement. Particle size and sphericity were estimated, even though drill chips can be irregular and span a broad distribution; the largest particles may determine whether clearing succeeds. The model also stops at the borehole exit and does not address how discharged cuttings will be diverted from the surface opening. The researchers recommend full-scale tests at depths approaching 25 meters, experiments that resolve the transition between recirculation and clearing more finely, computational-fluid-dynamics simulations, reduced-gravity testing, and trials using realistic regolith and ice mixtures. Despite these limitations, the agreement between model and observations supports pneumatic chip clearing as a plausible component of future Martian water-mining systems.

Subject of Research: Pneumatic removal of drill cuttings during Martian water-ice extraction

Article Title: Deep drilling on Mars: pneumatic chip clearing model for the RedWater mining system

Article References: Stolov, L., Palmowski, J., Zacny, K., Yen, B., Mellerowicz, B., Mank, Z., Sanasarian, L., & Schultz, J. (2026). Deep drilling on Mars: pneumatic chip clearing model for the RedWater mining system. Space and Planetary Resources, 2(1), Article 7. https://doi.org/10.1007/s44461-026-00013-y

Image Credits: AI Generated

DOI: 10.1007/s44461-026-00013-y

Keywords: Mars, water ice mining, planetary drilling, pneumatic conveying, RedWater, in-situ resource utilization, coiled tubing, thermal-vacuum testing, Deep, drilling, pneumatic, chip

The scientific case begins with the remarkable diversity of icy environments. Lunar water is expected primarily in permanently shadowed regions near the poles, where crater interiors can remain extremely cold because sunlight never reaches their floors. These “cold traps” may preserve water delivered by comets, asteroids or solar-wind chemistry over geological time. Some deposits could be mixed unevenly through fine-grained regolith, while others may occur as surface frost or buried layers. Mars presents a different opportunity: radar observations and orbital measurements indicate extensive subsurface ice, including exposed or shallowly buried sheets in some mid-latitude regions. On the icy moons of the outer Solar System, water ice forms the dominant outer shell, often above a global ocean. Europa and Enceladus are especially compelling because their interiors may contain liquid water in contact with rock, creating environments that could support chemical energy gradients relevant to life. Yet the ice that is scientifically most interesting is often the ice that is hardest to reach.

The review emphasizes that “water ice” is not a single engineering material. Its behavior depends on temperature, pressure, porosity, grain size, impurities, fractures and the amount of regolith or salt mixed into it. At the lunar poles, a drill may encounter abrasive dust, compacted soil and ice concentrations that vary over centimeter scales. On Mars, ice can be cemented into soil or layered with dust and carbon-dioxide frost. In the outer Solar System, ice may be exceptionally cold, mechanically strong or altered by radiation. The mechanical properties of such material remain uncertain before a spacecraft arrives, and even small errors in estimating hardness or cohesion can cause a drill to jam, overheat or consume more power than its lander can supply. Weak gravity creates an additional problem: on the Moon and small bodies, the downward force that helps a terrestrial drill bite into the ground is greatly reduced. The machine must push against the surface without lifting or destabilizing the spacecraft.

Mechanical drilling is therefore both familiar and hazardous. A rotating or reciprocating drill can break ice and regolith, while auger flights or other mechanisms transport cuttings toward the surface. Coring systems can preserve a cylindrical sample, allowing scientists to study the sequence of layers and the distribution of volatile compounds. But rotation generates reaction torque, which must be resisted by the lander or a dedicated anchoring system. The drill’s cutting teeth may wear rapidly in abrasive material, and loose chips can clog transport paths in a vacuum. In a conventional borehole, fluids may cool the drill and carry debris away; in space, those fluids could boil, freeze or contaminate the sample. The review identifies a central design tension: systems optimized for rapid excavation may mix or heat the material, whereas systems optimized for pristine scientific sampling are slower, heavier and more complex. A successful device may need interchangeable tools capable of switching between reconnaissance, resource extraction and carefully documented sample collection.

Thermal melting probes offer a radically different strategy. Instead of mechanically crushing ice, a heated tip melts a narrow pathway and moves downward through it. The melted water can sometimes be routed or refrozen behind the probe, while electrical or nuclear power supplies the heat. Because the probe does not need to remove large quantities of cuttings, it can potentially penetrate deeper than a conventional drill and avoid some problems caused by mechanical debris. This approach is particularly attractive for ocean-world concepts, in which a cryobot could descend through kilometers of ice to release instruments or a submersible into an underlying ocean. However, the physics is unforgiving. Heat must be sufficient to melt ice at the probe’s tip but not so excessive that energy is wasted into the surrounding material. Under low pressure, water may boil or rapidly sublime rather than form a stable meltwater channel. Dust layers, bubbles, fractures and salts can change the melting rate, while refreezing may trap the probe or seal communications and power pathways.

Deep-ice missions also face a communications problem that is easy to underestimate. A probe traveling below an ice shell cannot rely on a direct radio link to a spacecraft or lander at the surface. It may need a tether carrying power, data and perhaps mechanical strength, but deploying a tether through a narrow, winding melt channel introduces friction, tension and the risk of snagging. An autonomous cryobot must also know where it is, detect obstacles and recognize transitions between different ice layers. Acoustic navigation, inertial sensors, temperature probes, pressure measurements and optical or chemical instruments could work together to build a map of the subsurface. The review points toward intelligent sampling systems that can change their behavior as conditions evolve. A probe might reduce speed in a dusty layer, alter heater power when the ice becomes porous, or select a side path after detecting a fracture. Such autonomy is not simply a convenience: at the Moon, Mars or an icy moon, communication delays and limited opportunities for intervention make real-time control from Earth impossible.

Surface sampling devices remain crucial because many missions will begin with shallow investigations rather than ambitious deep drilling. Robotic arms, scoops, scrapers, corers and small drills can test whether a suspected deposit contains accessible water and can measure how that resource is distributed. The Phoenix lander demonstrated the scientific value of acquiring icy soil on Mars, while more recent lunar exploration has strengthened the case for studying both surface and subsurface hydration. At the lunar poles, however, the environment complicates even a simple scoop. Permanently shadowed terrain may be colder than the equipment’s operating range, while nearby sunlit slopes can expose instruments to severe thermal cycling. Regolith grains can cling electrostatically to mechanisms, obscure cameras and abrade seals. A sampling tool must also prevent volatile loss: once ice is excavated and exposed to vacuum, it can sublimate directly into vapor, changing the sample before it reaches an analyzer. Containment, temperature control and rapid transfer may be as important as the cutting action itself.

The technological challenge becomes more severe when the goal shifts from detecting water to using it. In-situ resource utilization systems would heat ice-bearing soil, capture the released vapor and separate water from contaminants. Water could then be purified for life support or electrolyzed into hydrogen and oxygen, producing propellant and breathable oxygen. But extraction efficiency depends on concentration, grain size, temperature and the strength of the bond between water and surrounding minerals. A system designed for lunar polar ice may not work for hydrated minerals at lower latitudes, where water is chemically bound rather than present as discrete ice. Processing equipment must operate with little power, limited maintenance and no possibility of importing replacement parts. It must also balance industrial throughput against planetary protection and scientific preservation. Excavating a resource deposit could disturb a record of cometary delivery, solar-wind chemistry or ancient climate. The review therefore treats sampling and resource use as linked but distinct objectives, requiring mission planners to decide how much material can be consumed and how much must be archived.

Sample return remains one of the most powerful future directions because laboratory instruments on Earth are vastly more capable than most spacecraft payloads. A returned ice or volatile-bearing sample could be examined with high-resolution spectroscopy, mass spectrometry, microscopy and isotope analysis, revealing its molecular history and possible biological signatures. Yet returning ice is harder than returning dry rock. The sample may warm, melt, sublime or chemically react during collection, ascent, transit and landing. Containers must maintain a controlled temperature and pressure while surviving launch vibrations and the journey between worlds. If material from Europa or Enceladus is ever collected, contamination control will become especially stringent because scientists must distinguish indigenous chemistry from terrestrial biological or organic contamination. A sample-return architecture may consequently require cryogenic storage, sealed transfer chambers and multiple layers of sterilization and verification. The review presents such missions not as a single technological leap but as a chain of tightly coupled systems, in which a failure at any stage can erase the scientific value of the sample.

The authors conclude that the future of extraterrestrial ice exploration will depend less on one spectacular drilling design than on the integration of many capabilities. The most valuable systems will combine compact mechanical tools, thermal methods, surface collectors, sensors and analytical instruments in packages able to adapt to uncertain terrain. Low mass and low power are essential because every kilogram launched into deep space carries a major transportation cost, while every watt may compete with communications, heating and science operations. High reliability is equally important: extreme cold can embrittle materials, vacuum can degrade lubricants and radiation can damage electronics. Multifunctional robots could first map a deposit, then characterize its mechanical properties, extract a controlled sample and finally support limited water production. If these technologies mature, water ice could become both a scientific archive and the infrastructure of exploration—a substance that helps answer how worlds evolve while also supplying the resources needed to visit them. The frozen Solar System may be difficult to mine, but it could ultimately make the Solar System far easier for humans to explore.