No Spacecraft Can Affordably Survive 14 Days of Lunar Darkness at -233°C

The lunar day-night cycle lasts 29.5 Earth days — 354 hours of sunlight followed by 354 hours of continuous darkness. During the lunar night, surface temperatures at the south pole drop to -233°C (40 K), colder than any natural temperature on Earth. No current spacecraft, rover, or instrument can affordably survive this environment without radioisotope power sources, which are prohibitively scarce and expensive. This is NASA's #1-ranked civil space technology shortfall by broad consensus across all stakeholder groups. The problem is a fundamental thermal-energy design dichotomy: hardware must reject heat during the 120°C lunar day and retain heat during the -233°C lunar night — a 350°C swing — using a single system.

Every current and planned lunar surface mission — Artemis rovers, science stations, habitats, ISRU plants — is constrained by the lunar night. A rover that cannot survive lunar night is limited to a single 14-day operating window per landing, drastically reducing science return per dollar. NASA's Lunar Terrain Vehicle must survive at least 85–125 hours of lunar night darkness while accommodating two EVA-suited astronauts and 800 kg of payload. A Surface Habitat must offset 1,550 W of continuous heat leak during eclipse to maintain a habitable 283 K interior. Without solving this problem, sustained human presence on the Moon is architecturally infeasible.

The Soviet Lunokhod rovers (1970–1973) survived up to 10 months on the lunar surface using radioisotope heater units (RHUs) fueled by polonium-210, but RHUs and RTGs depend on plutonium-238, whose global production is measured in kilograms per year and costs ~$8 million per kilogram. The U.S. ALSEP packages ran flawlessly for up to 98 lunar day/night cycles using RTGs, but the supply of Pu-238 cannot support more than a handful of missions. Battery-only survival is prohibitively heavy: surviving one lunar night with conventional Li-ion batteries for a 100 We load requires approximately 432 kg of batteries — more than most lander payloads can accommodate. Thermal wadi concepts (storing solar heat in regolith thermal masses) have been proposed but never tested in situ and face challenges in controlling heat transfer rates. Loop heat pipes with thermal control valves (5 W/K ON, 0.002 W/K OFF switching ratio) have been developed but are unproven under true lunar conditions over multiple thermal cycles.

A practical solution requires one or more of: (1) a high-switching-ratio thermal management system that can switch between heat rejection and heat retention modes across the 350°C diurnal range without degrading over hundreds of cycles; (2) energy storage with dramatically higher specific energy than Li-ion (current ~200 Wh/kg) to reduce survival battery mass to acceptable levels; (3) alternative non-radioisotope heat sources such as phase-change thermal storage with appropriate melting points, or (4) in-situ thermal mass utilization (regolith wadis) validated under actual lunar conditions. The most promising near-term approach may be combining advanced thermal switching with modest energy storage, rather than solving either problem in isolation.

A student team could prototype and test a high-switching-ratio thermal switch mechanism, measuring ON/OFF conductance ratio and cycling durability in a relevant temperature range. The key design challenge is achieving high ON-state conductance (for daytime heat rejection) while minimizing OFF-state conductance (for nighttime heat retention) — students would learn that the physics of thermal insulation and thermal conduction are fundamentally in tension. A materials-focused team could investigate and compare high-energy-density phase-change materials for thermal storage in the 0–50°C range, characterizing their melt-freeze behavior over hundreds of cycles. Skills in heat transfer, materials science, and thermal testing would be most relevant.