HVAC in Space: How We Heat, Cool, and Survive Beyond Earth

Heating, Ventilation, and Air Conditioning (HVAC) on Earth is about comfort and safety. In space, HVAC systems are about surviving extreme hot and cold temperatures.

Whether in the stratosphere aboard a jet, inside the vacuum of a rocket, or under a pressurized dome on Mars, temperature control and air management are essential for human life, and the laws of physics create both constraints and opportunities.

In this article, you’ll see how HVAC systems adapt for survival in extreme environments – from high-flying jets to space stations, and future Martian habitats.

HVAC Challenges Beyond Earth

In space, HVAC systems face a unique challenge: no air means no easy way to move heat.

“The key challenge for HVAC systems in most off-planet environments is the absence of an atmosphere,” says Joseph Kenrick, Interim Program Execution Manager at Lunar Outpost. “On Earth, excess heat is primarily dissipated through convection and conduction to the surrounding air. However, in space or on airless bodies like the Moon, there is no air to conduct or convect heat away from the system.”

Without that natural transfer, heat from electronics and life support systems can quickly build up, risking overheating and equipment failure. To manage this, space-based HVAC systems use closed fluid loops that circulate heat internally. That heat is then moved to external radiators, which release it into space via thermal radiation – the only effective heat transfer method in a vacuum.

“Off-planet HVAC systems must rely on internal conduction and forced convection... to transport heat to radiators,” Kenrick explains.

HVAC at High Altitudes in Airplanes

Environment:

• Temperature: Can drop to -40°C to -70°C (-40°F to -94°F) at cruising altitudes (~35,000 ft).
• Pressure: About 25% of sea-level pressure.

Systems Used:

These systems maintain cabin temperatures around 21-24°C (70-75°F) and oxygen levels at safe levels by cycling in filtered, pressurized air.

HVAC in Rockets (From Mercury to Starship)

Environment:

• Space Temperature: Technically ~3K (-454°F) in shadow; hotter than boiling in sunlight.
• Atmosphere: None. Vacuum means no air to transfer heat by convection.

Early Use Cases:

• Mercury/Gemini/Apollo Capsules: Used sublimators (ice exposed to vacuum) to dump waste heat and liquid cooling garments worn by astronauts.
• Space Shuttle: Used a combination of radiators, Freon loops, and sublimators.

Modern Rockets & Starship (SpaceX):

• Radiators to reject heat via infrared radiation.
• Active cooling loops for electronics and life support systems.
• Thermal tiles on the exterior for reentry, but not for HVAC.

Why Radiation Dominates:
In space, there's no air for convection. So, heat must be radiated via infrared emission, which is far less efficient. This is why radiators must be large and positioned carefully to avoid overheating or freezing.

Heating Martian Rovers:
NASA’s Martian rovers, such as Curiosity and Perseverance, rely on a combination of insulation and radioactive decay for heat. These robotic explorers are equipped with Multi-Mission Radioisotope Thermoelectric Generators (MMRTGs), which convert heat from decaying plutonium-238 into electricity.

In addition to powering systems, the excess heat is circulated internally to prevent the freezing of critical components like batteries and electronics – especially during the long, subzero Martian nights or solar-obscuring dust storms.

This concept was dramatized in the movie The Martian, where astronaut Mark Watney uses the heat from a buried plutonium-powered RTG to stay warm while traveling across Mars in a pressurized rover. While the scenario is rooted in real technology, there are significant engineering and safety challenges to using an RTG in a crewed vehicle.

In reality, future Mars rovers designed for human travel would likely use a combination of heavily insulated cabins, onboard thermal batteries, and either electrical or nuclear-powered climate control systems. Radiative panels or thermal mass materials may also be integrated to stabilize internal temperatures.

Unlike robotic rovers, human-rated systems must protect life for extended periods, with fail-safes, controlled heat distribution, and breathable pressurized environments.

HVAC in Space Stations (ISS and Beyond)

International Space Station (ISS):

• Temp Outside: -157°C (-250°F) in shadow to +121°C (250°F) in sunlight.
• Internal Temp: Maintained around 22°C (72°F).

Systems Used:

• Active Thermal Control System (ATCS):
  • Two ammonia loops outside station → radiate excess heat.
  • Water loops inside for temperature regulation.
• Condensing Heat Exchangers: Remove moisture and CO₂.
• Air circulation fans: Prevent CO₂ pockets and "hot spots."

Physics Factor:
Heat must move from electronics and humans → water loop → ammonia → radiators → space. Must avoid overheating but also must heat some systems to prevent freezing.

Lunar Bases: Future Moon Colonies

Environmental Challenge:

• Lunar day (~14 Earth days): +127°C (260°F)
• Lunar night (~14 Earth days): -173°C (-280°F)
• No atmosphere = no insulation or convection.

HVAC Needs:

• Pressurized Habitats with active climate control.
• Thermal mass walls, buried structures, or regolith insulation to buffer against extremes.
• Likely to use radiator panels, heat pumps, and phase-change materials for temperature stability.
• Air revitalization with CO₂ scrubbers, humidity control, and pressure regulation.

HVAC on Mars: Cold, Thin, Dusty

Mars Environment:

• Temperature: Averages -63°C (-81°F); extremes from -125°C to +20°C.
• Atmosphere: ~1% of Earth’s, mostly CO₂. Little insulation or oxygen.
• Dust Storms: Can last months and block solar energy.

HVAC Concepts for Mars Habitats:

Some designs borrow from passive house architecture on Earth but must handle the radiation, pressure, and isolation of Mars.

Key HVAC Engineering Considerations

Heat Transfer in a Vacuum:

• No convection; only radiation and conduction matter.
• Radiators must be large and well-placed.

Energy Use:

• Power is limited on spacecraft and colonies; HVAC systems must be efficient.
• On Mars, solar power is unreliable due to dust; nuclear is more viable.

Closed-Loop Systems:

• Can’t waste water or air – every molecule counts.
• Air revitalization and recycling are part of HVAC strategy.

Designing HVAC Systems for Other Worlds

HVAC in off-planet environments is far more than temperature comfort – it's a matter of life support. Whether managing supercooled airplane cabins, sub-zero spacecraft, or dusty Martian domes, engineers must consider the absence of atmosphere, extreme temperatures, and limited energy.

These challenges push us to invent new systems: from radiation-based cooling to thermal mass buffering, to bioregenerative life support.

As we return to the Moon, aim for Mars, and potentially build floating cities in orbit, HVAC will be one of the most critical technologies in our survival toolbox – quietly working behind the scenes to keep the next generation of explorers alive.