New Mars Forums

For SpaceNut re interesting post about heat loop on Mars.

https://newmars.com/forums/viewtopic.ph … 93#p237493

Your AI friend seems to have understood that the temperature of the regolith a few meters down is a reliable number, well below the freezing point of water. In another topic, kbd512 added a post to one of Void's topics about use of SCO2 for a geothermal energy harvesting system.

Please ask your AI friend to design a heat pump system that will harvest planetary thermal energy on Mars.

I am hoping the idea is practical, because it would solve a lot of pesky problems.  We humans are going to have to invest energy to live on Mars, so learning how to leverage our investment to harvest thermal energy from the planet itself seems to me like something well work pursuing.

(th)

Solar thermal propulsion (STP) utilizing a hydrogen propellant, enhanced by heat pipe technology and leveraging high-performance, regeneratively cooled engine techniques (similar to the Merlin engine's regenerative cooling), is a highly efficient propulsion concept for in-space transportation. This approach, often characterized as a Solar Powered Rocket with Impulsive Thermal Engine (SPRITE), can achieve specific impulse (\(I_{sp}\)) values of 830–1000+ seconds, roughly twice that of the best chemical engines. Key Components &

Technology Hydrogen Propellant: Used for its low molecular weight, providing superior \(I_{sp}\) (800-1000+ seconds) compared to other propellants.

Heat Pipe/Thermal Storage: High-temperature sodium wicking or phase-change materials (PCM) are used to store solar energy, enabling the system to "coast" and accumulate energy, then release it for high-thrust, intermittent burns.

Materials: Refractory metals such as tungsten or rhenium are required to handle high temperatures (>2500K) and prevent chemical degradation from hot hydrogen.

"Merlin" Capabilities (Regenerative Cooling): Similar to the SpaceX Merlin engine, which uses regenerative cooling to handle extreme temperatures, solar thermal engines use the cold hydrogen propellant to cool the engine chamber and nozzle before it is heated and expelled. 

Performance Characteristics Thrust & Efficiency: While early designs produced around 8.9 N of thrust, advancements in high-temperature materials and concentrator technology are aimed at increasing performance.

Energy Collection: Uses deployable solar concentrators to gather solar energy over time, eliminating the need to have collectors pointed at the sun during all maneuvers.

Propellant Management: To handle cryogenic hydrogen, advanced zero-boil-off (ZBO) techniques are used to ensure long-term storability. 

Operational Advantages High Specific Impulse (\(I_{sp}\)): Over 800s to 1000s, significantly higher than chemical (\(I_{sp}\) ~300-450s).

No Hazardous Materials: Unlike nuclear thermal propulsion (NTP), solar thermal systems are generally non-toxic and safer to operate.High-

Thrust Capability: The use of energy storage/impulsive thermal engines allows for high-thrust maneuvers suitable for orbital transfers (e.g., LEO to GEO in ~1 month).

Versatility: The system is ideal for in-space tugs, utilizing on-orbit refueling or potentially harvested water/hydrogen as propellant. Current research, such as the NASA-supported SPRITE project, is focused on reducing the total wet mass of these vehicles to below 200 kg while maximizing propellant efficiency

Solar thermal propulsion (STP) using hydrogen heat pipes represents a high-efficiency alternative to traditional chemical engines like SpaceX's Merlin. While STP systems excel in fuel efficiency (Isp), they operate at vastly different scales than the high-thrust Merlin engines used for heavy lifting.

1. Comparative Capabilities (STP vs. Merlin)
As of 2026, experimental STP systems are achieving performance metrics that surpass the efficiency of Merlin engines while trailing significantly in raw power.

Specific Impulse (Efficiency): STP systems such as the SPRITE (Solar Powered Rocket with Impulsive Thermal Engine) achieve an Isp of ~830–860 seconds. Advanced designs using carbide materials aim for >1,000 seconds. In contrast, the Merlin 1D vacuum engine has an Isp of ~348 seconds.

Thrust-to-Weight Ratio: The Merlin 1D holds a world record thrust-to-weight ratio of >150. While STP systems like SPRITE are designed for high thrust-to-weight relative to other solar concepts, they generally produce low absolute thrust (e.g., 8.9 N) suitable for orbital transfers rather than Earth-to-orbit launches.
Mission Utility: STP is primarily targeted for upper-stage maneuvers, such as moving payloads from LEO to GEO or the Moon, where high efficiency over long durations is more valuable than the immediate raw thrust required by first-stage engines like the Merlin.

2. Role of Hydrogen Heat Pipes in 2026
In 2026, hydrogen heat pipes are critical for thermal management in these high-temperature systems:

Thermal Transport: Heat pipes function as "thermal superconductors," using phase-change fluids to move massive heat loads from solar concentrators to the engine's absorber cavity with minimal temperature drops.

System Enhancement: Recent developments show that integrating parabolic reflectors with advanced heat pipes can increase local temperatures by over 30%, significantly improving the melting performance of phase-change materials used for energy storage.

Propellant Management: Solar thermal rockets utilize hot hydrogen as a propellant because its low molecular weight allows for much higher exhaust velocities than the kerosene/oxygen mix used in Merlin engines.

3. Current Milestones (2025–2026)

Full-Scale Tests: In late 2025, companies like Portal Space Systems validated STP architectures at temperatures of 1,500°C (2,700°F) using electrical induction to simulate solar power, with full-scale demonstration missions scheduled for 2026.

Advanced Materials: Research in 2026 continues to focus on refractory metals (tungsten, rhenium) and high-temperature carbides to withstand the 2,500K+ environments required for efficient hydrogen heating

A solar thermal optical plane space vessel uses focused sunlight via large mirrors/concentrators, often with optical fibers, to heat a propellant (like hydrogen) to extreme temperatures, creating thrust, offering high efficiency (high specific impulse) for orbit changes, unlike solar sails that use light pressure, with concepts like Portal Space Systems' Supernova aiming for high maneuverability for defense/service, building on NASA's research for advanced solar propulsion systems.
Core Concepts
Solar Thermal Propulsion (STP): Captures solar energy with large mirrors (concentrators) and focuses it onto a heat exchanger/absorber, heating a propellant to generate thrust, achieving higher efficiency than chemical rockets.
Optical Waveguides: Some designs use optical fibers to transmit concentrated solar energy from the collector to the engine, allowing for more flexible system designs.
Optical Plane: Refers to the precise optical systems (mirrors, lenses) used to concentrate sunlight and potentially for imaging/sensing, requiring high-temperature materials and stability.
Key Components & Technologies
Concentrators: Large, often inflatable mirrors that focus sunlight.
Absorber/Heat Exchanger: Receives concentrated solar energy and heats the propellant.
Propellant: Typically hydrogen, heated to over 2500K, sometimes over 3000K with advanced materials.
Materials: Requires high-temperature refractory metals (tungsten, rhenium) or carbides to withstand extreme heat.
Optical Structures: Precision-built composite structures for stability in imaging and concentrating systems, used in telescopes and rovers.
Applications & Examples
Upper Stages: Ideal for moving payloads from Low Earth Orbit (LEO) to higher orbits or Earth escape.
Small Satellites: Enables orbit changes and long-duration missions with high delta-V.
Portal Supernova: A current project using solar thermal propulsion for high-delta-V, in-orbit refueling, and autonomous drone swarms.
NASA Research: Historically studied by NASA Marshall Space Flight Center (MSFC) and Sandia National Labs for advanced propulsion.
Contrast with Solar Sails
Solar Sails: Use direct photon pressure from sunlight on large sails, no propellant needed (e.g., IKAROS, LightSail-2).
Solar Thermal: Heats a propellant for rocket thrust; distinct from solar sails but both use solar energy for propulsion

Building a large-scale stainless steel isogrid dome on Mars to house 1,000 crew members requires an industrial-scale, multi-decade construction effort, focusing on in-situ resource utilization (ISRU) to minimize the immense cost of transporting materials from Earth.

Structural Design and Engineering Isogrid Structure: An isogrid—a triangular pattern of ribs—provides high stiffness-to-weight ratios, ideal for resisting the high tensile stresses of a pressurized dome against the near-vacuum of Mars.

Dome Sizing: To house 1,000 people, the structure would likely need to be a large, multi-hectare habitat, similar to "mega dome" concepts.

Dimensions: A 20-meter high, 24mm thick steel plate wall, bolstered by vertical stringers, can withstand internal pressure.

Anchoring: Large domes create immense upward pressure (approx. 10 tonnes per \(m^{2}\)). The dome must be anchored deeply into the ground, likely using the weight of Martian regolith.

Construction Process and Materials Stainless Steel Sourcing: Stainless steel components can be fabricated on-site. Using locally sourced materials requires 40-50 years of development, involving heavy mining and smelting, with a 1-meter deep, 8x8 km pit of regolith necessary for material to sustain a large population's infrastructure.

Fabrication: Panels would be manufactured on Mars and welded in place to create a pressure-tight, airtight structure.

Prefabrication Limits: Due to transport constraints, domes cannot be brought in one piece; they must be constructed using modular, assembled components.

Protection: The steel shell must be shielded from radiation and micrometeoroids, typically by covering it with 1–3 meters of compacted Martian regolith.

Challenges and Considerations Atmospheric Pressure: The 78,000 tonnes of force on a 100-meter dome requires massive, specialized structural engineering.

Surface Conditions: Extreme cold and dust storms will hinder construction, requiring durable, automated robotic equipment.

Alternative Approaches: While steel is possible, some experts suggest that 3D-printed regolith, ice, or carbon fiber might be more efficient in terms of weight and material, as bringing steel from Earth is too costly.

Redundancy: To prevent single-point failures, the habitat should consist of multiple interconnected domes rather than one single, massive structure

Stainless steel isogrid dome construction on Mars offers a robust method for creating large-volume, pressurized habitats, leveraging high-strength, lightweight, and durable materials that can be transported from Earth or potentially manufactured on-site. Isogrid structures (triangular, lattice-reinforced, or sandwich panels) are engineered for maximum stiffness, providing the necessary pressure vessel strength to withstand the high-pressure differential (approx. 14.6 PSI) between a breathable, pressurized interior and the near-vacuum, low-pressure (0.1 PSI) Martian environment.
Key Aspects of Stainless Steel Isogrid Dome Construction on Mars
Structural Integrity: Isogrid designs, often used in aerospace for their exceptional strength-to-weight ratio, are considered for large domes to manage the massive tension loads on the dome surface. These designs use stiffeners to prevent the panels from "ballooning".
Material Advantages: Stainless steel is deemed more cost-effective to produce and, for certain applications, more reliable than inflatable alternatives. SpaceX, for instance, has developed technologies to work with stainless steel for large pressure vessels.
Construction Process:
Modular Assembly: Domes would likely be constructed from smaller, manageable panels rather than being sent as one large unit, given cargo constraints (e.g., SpaceX's 12m diameter limit).
Welding and Joining: Electron beam welding or similar advanced, automated techniques would be used to join panels, taking advantage of the vacuum of space (or, by extension, the Martian atmosphere) for high-quality welds.
Foundations: The structure would likely be anchored firmly into the Martian regolith to withstand internal pressures and environmental stressors.
Environmental Protection: While the steel provides the pressure vessel, additional layers are needed for radiation shielding and to handle the extreme temperature differences (around -63°C average).
Regolith Shielding: Covering the dome with 3–5 meters of local soil (regolith) is proposed to protect against high radiation levels and micrometeoroid impacts.
Hybrid Designs: Using a "thermos" style, with an inner pressurized steel hull and an outer shell, is a potential design to manage thermal and structural loads simultaneously.
Potential Challenges:
Massive Pressure Load: A large, unburied dome would need to be extremely heavy to prevent it from bursting. This requires significant anchoring and material strength.
Transport Costs: Moving large amounts of steel from Earth is expensive, necessitating, in the long term, on-site, in-situ resource utilization (ISRU) to create construction materials.
Stainless steel isogrid domes are a viable, high-tech option, often discussed in parallel with other techniques like 3D-printed ice habitats or underground, excavated, or "buried," in-situ, "dome-on-a-crater" concepts

Constructing a stainless steel isogrid dome on Mars to maintain an internal atmosphere of 0.5 bar (approx. 7.25 psi, similar to Apollo-era spacecraft) is an engineered solution designed to balance high structural efficiency with the need to withstand intense internal tensile stress. At this pressure, the dome is primarily a pressure vessel, requiring superior anchorage to prevent it from lifting or buckling.

1. Structural Design & Advantages (Isogrid)
An isogrid structure—a triangular, lattice-like reinforcement on the interior of the skin—is ideal for a Mars dome because it offers high bending stiffness with minimal material weight.
Tensile Strength: Because the 0.5 bar internal pressure far exceeds the 0.006 bar external pressure, the dome is under constant, significant tension. Isogrid structures efficiently manage these hoop stresses.
Material Selection: Stainless steel is favored for its high strength-to-weight ratio, ease of welding/prefabrication on-site, and high cryogenic strength at low temperatures.
Shape Optimization: While geodomes are common, low-pressure Mars environments might favor "egg-like" or flatter shell geometries to better distribute the internal pressure loads.

2. Construction Methodology on Mars
Constructing such a structure requires automated, robotic assistance to handle hazardous, low-pressure, and cold conditions.
Prefabrication and Welding: Stainless steel panels can be pre-manufactured on Earth and transported, then welded together on-site. Welding is considered feasible for stainless steel compared to other materials like carbon fiber.
Anchorage: The dome must be heavily anchored to the Martian surface to prevent it from lifting off, requiring foundation engineering or covering the dome with several meters of regolith (soil) for ballast and radiation shielding.
In-Situ Resource Utilization (ISRU): Long-term construction can leverage ISRU by producing steel on Mars using local iron oxide and carbon, although this is a long-term goal.

3. Key Challenges at 0.5 Bar
Pressure Management: The dome must maintain its structural integrity under constant outward pressure, necessitating robust sealing against air loss.
Material Embrittlement: Although stainless steel has good low-temperature properties, it must be carefully selected to avoid becoming brittle in extreme cold.
Dust Accumulation: Abrasive Martian dust can settle on the dome, reducing solar gain and requiring maintenance.
Radiation Protection: While 0.5 bar of pressure provides some, it is insufficient to block harmful cosmic radiation; therefore, a covering of regolith is often necessary.

4. Comparison with Alternatives
vs. Rigid Domes: Stainless steel isogrid provides superior strength over standard rigid domes but is heavier to transport.
vs. Inflatable Domes: While lighter, inflatable structures (like the NASA Ice Home concept) require thicker insulation layers to prevent freezing and, often, a protective outer shell.
vs. Cut-and-Cover: Using buried or "cut and cover" techniques is often preferred for long-term, high-pressure habitation to minimize tension, whereas isogrid domes are excellent for high-volume work/living spaces.
A 0.5 bar environment represents a balance between the high cost of maintaining a 1-bar Earth-like atmosphere and the metabolic needs of humans, making it a viable, high-efficiency compromise for Martian habitation

Yes, an isogrid structure made from flat stainless steel sheets is a viable concept for large Martian habitats, offering high strength-to-weight with triangular ribs from single sheets, ideal for withstanding Martian pressure/loads while being potentially manufacturable (even 3D printed) in-situ or from pre-fab, balancing lightweight needs with Mars's harsh environment, though material processing and thermal swings remain key challenges.
Why Isogrids Work for Mars:
Strength & Lightness: Isogrids, essentially thin skins with stiffening ribs (often triangular), provide high structural stiffness and strength while minimizing mass, crucial for space structures.
Single-Sheet Fabrication: They can be machined or printed from single sheets, reducing complex assembly and potential leak points compared to honeycomb structures.
Isotropic Properties: The triangular pattern makes them behave like an isotropic material (same properties in all directions), offering uniform performance.
Material Adaptability: While traditionally metal, new additive manufacturing allows printing composite isogrids, and stainless steel offers durability.
Stainless Steel & Mars:
Durability: Stainless steel offers excellent resistance to corrosion and extreme temperatures, making it suitable for the harsh Martian environment.
Manufacturability: While requiring significant energy, it's a known material, and techniques like additive manufacturing (3D printing) are being explored for creating these structures on Mars using local resources or brought materials.
Challenges & Solutions:
Thermal Swings: Extreme temperature variations on Mars (e.g., 20°C to -73°C) can affect material adhesion and performance, requiring software/design solutions.
In-Situ Resource Utilization (ISRU): Processing Martian regolith or imported steel into printable/formable sheets for these structures is a major engineering hurdle.
Habitat Design: Integrating isogrid panels with other systems (like regolith shielding for radiation) and ensuring airtightness for large volumes remains complex.
In essence, an isogrid made from flat stainless steel sheets is a strong structural choice, but its practical application on Mars hinges on advanced manufacturing and material science to overcome thermal and processing challenges

Isogrid technology, which involves creating rigid, lightweight triangular-stiffened structures, is a critical technique for designing space-hardened habitats and shells on Mars. While specific "plug-and-play" software labeled "Isogrid Maker for Mars" does not exist, aerospace and structural engineers use several advanced CAD and simulation tools to model these, often utilizing additive manufacturing (3D printing) for implementation.
Key Software and Modeling Techniques for Mars Domes:
Autodesk Fusion 360: Used for parametric modeling of isogrid structures. It allows engineers to create, test, and adapt the geometry of triangular ribs, which is critical for optimization.
Continuous Composites (CF3D): NASA-selected technology that uses advanced robotics to print continuous carbon fiber in isogrid rib patterns for space applications.
Finite Element Analysis (FEA) Software: Tools like ANSYS or NASTRAN are used to simulate the structural loads (internal pressure vs. external atmosphere) on isogrid domes to ensure they can withstand Martian conditions.
Roboze One+400: A 3D printer specifically used in research for producing high-performance, lightweight isogrid structures.
Geodesic Dome Calculators: For the basic geometry of polyhedral domes, tools that calculate chord factors and strut lengths are used.
Applications on Mars:
3D Printed Shells: Research suggests using 3D-printable inner spherical shells and outer parabolic domes to protect habitats from the Martian climate.
Regolith Manipulation: Techniques like sintering or microwave melting of Martian regolith are planned for creating geodesic domes.
Structural Efficiency: Isogrid designs are used to minimize mass while maximizing pressure resistance, necessary for transporting materials from Earth or using indigenous resources.
Commonly Used Tools:
CAD: Autodesk Fusion 360, SolidWorks, CATIA.
Analysis: ANSYS, Abaqus, Altair HyperWorks.
Manufacturing: Specialized 3D printing software (slicers for robotic arms).
These tools are part of a broader approach to designing and testing Martian habitat structures, which must be both lightweight for transit and rigid enough to handle the 101 kPa pressure differential on Mars