Sven Gunnar Bilén

In plain 3D printed concrete (3DPC), in-plane compressive anisotropy is governed mainly by directional pore structure, but this view is insufficient when fibers are added. Here, plain 3DPC and 3D-printed fiber-reinforced concrete (3DP-FRC) with 0.5 vol.% basalt fibers were printed using three raster patterns and compared with cast counterparts. Fiber addition reduced the mean pore aspect ratio by 13–19% and weakened path-induced pore alignment, even though pore area increased. A directional pore-defect index described the strength loss of plain 3DPC but overpredicted five of the six 3DP-FRC cases, showing that pore changes alone could not explain the response. Including path-based fiber orientation showed that the transverse-fiber contribution depends on the directional pore penalty rather than acting independently, increasing R2 from 0.27 to 0.93. Finite-element simulations agreed with the experimental directional strength ratios within 5.4% and supported a transition from compression-dominated response of load-aligned fibers to tension-dominated response of transverse fibers. Overall, fiber addition reduced in-plane anisotropy by 53.8–63.5%, showing that pore structure and fiber orientation jointly contribute to the compressive response of 3DP-FRC.

This chapter presents a modular habitat design strategy for Mars, aimed at advancing human exploration through scalable, resilient structures built using autonomous additive construction (AAC) and in situ resource utilization (ISRU). The design leverages local Martian regolith and robotic fabrication to minimize reliance on earth-based materials, creating sustainable habitats adaptable to the planet’s environmental conditions. Key design concepts include modularity for ease of construction, transportation, and reconfiguration, and a strategy for habitat expansion over time to accommodate growing mission needs. AAC systems enable efficient, flexible assembly and repair of habitat components, ensuring structural integrity in the face of the challenging climate on Mars. The chapter explores the integration of additive manufacturing techniques, particularly with in situ materials, and strategies for thermal regulation, optical transparency, radiation protection, and life-support infrastructure. This modular approach supports an evolving habitat framework that can be customized for diverse mission profiles, enhancing the feasibility and resilience of long-term human presence on Mars.

Precise control of the water-to-cement (w/c) ratio is critical in three-dimensional concrete printing (3DCP), for which minor deviations compromise extrudability, buildability, and structural integrity. Existing non-destructive w/c (moisture) sensors have not been validated for real-time, in situ monitoring during the concrete extrusion process. This study develops and validates a four-electrode Wenner-array probe, interfaced with an LCR meter, for in situ electrical resistance measurements of fresh concrete. The system was calibrated against NaCl and KCl electrolytic solutions at resistivities of 1, 5, and 10 Ω·m and then tested on ordinary Portland cement pastes at w/c ratios of 0.40–0.60 and on a proprietary 3D-printable blend at 0.40–0.65. The results show that resistance drift remained below 1.2% under ambient temperature fluctuations, with sub-second response times. Strong nonlinear correlations (R² > 0.99) were established between electrical resistance and w/c ratio for both formulations, with resistance increasing with higher w/c ratios due to ionic dilution and decreasing over time as early-age hydration progressed. Proprietary mixtures below w/c = 0.51 exhibited insufficient pore connectivity (CV > 30%) for reliable measurement, whereas mixtures at w/c ≥ 0.51 demonstrated excellent repeatability (CV < 2.80%). Electrical resistance measurement provides a viable real-time technique for w/c determination in fresh concrete, enabling automated closed-loop control in 3DCP operations.

Ground tests of microwave electrothermal thrusters (METs) are conducted under 1 g, where buoyant forces distort the plasma morphology and bias performance data. We investigate these effects in a 2.45-GHz, TMz011 cavity thruster operated with nitrogen over 200–2000 sccm and at 80–600 W. Three dimensionless surrogates — a modified Bond number Bo (buoyancy), a swirl group θ, and an electromagnetic anchoring group ΠEM — bring all experimental points onto a single, self-consistent scaling curve. Guided by these surrogates, we then recast the horizontal-nozzle data into a centered, reduced-order surrogate: a log-linear form in ṁ, Pin, and the stagnation-pressure ratio P0,h/P0,c with a single exponential nonlinearity in P0,h/P0,c. The inferred elasticities show displacement grows with mass flow while remaining only weakly sensitive to small, local changes in Pin or P0,h/P0,c; the dominant response is a sharp departure once P0,h/P0,c moves away from its near-optimal neighborhood. Orientation controls performance: with the nozzle upward, buoyancy helps anchor the discharge at the throat and P0,h/P0,c often approaches ~3:1 (peaking near 3.3–3.5), whereas in horizontal/downward tests buoyancy displaces the bubble off-axis, reducing P0,h/P0,c by ~20-40%. Equal top–bottom injection maximizes swirl confinement and suppresses buoyant drift. The surrogate offers a compact path to correct 1-g measurements toward flight-like conditions and to couple directly with thrust and Isp models for MET design.