Insulation

Sheets of foamed polystyrene for insulation of houses.

Insulation is needed to keep a colony warm and reduces the consumption of energy for heating. Aerogel or plastic foam may be utilized for insulation. Regolith may be heaped over buildings to keep in heat. Mineral wools, spun from local resources, may provide a lower tech alternative insulation. Fiberglass, a type of mineral wool, is commonly used as insulation on Earth. Arsenic is a mineral that can be used as a heat tolerant insulation, but is toxic to life.

The glass body of a vacuum flask.

Insulation on Mars

The thin Martian atmosphere has a reduced capability for a convective flow of heat. More important is the heat radiation, which can be effectively reduced by choosing the material of the building's surface. A smooth bright metallic surface emits much less heat radiation than a rough black one. A simple aluminium coated foil wrapped around the settlement modules provides excellent insulation. Multi-layer insulation (MLI) of the same type of foil can reduce heat loss to very low numbers and is commonly used for satellites. However, convection is still significant in insulation systems on Mars and this reduces the effectiveness of MLI to about the same as other systems.

Foam glass is another form or insulation than can be produced locally and should have superior insulation properties,as well as good structural properties. Foam insulation on Mars has very low convection and radiation rates. The heat transfer comes essentially from conduction in the cell walls.

Fiberglass and mineral wool would not function as insulators in the same way on Mars as they do on Earth. Fiberglass is not itself an insulator. The insulation comes from the thermal resistance of the air in the fiberglass mat. The resistance of the air in increased because it cannot flow freely over the surfaces, reducing convective heat transfer significantly. Fiberglass is also installed with a reflective vapor barrier, that adds to its insulation value.

A block of ice wrapped in aluminium foil to prevent melting.

Insulation table

The following table shows some insulation values for materials on Mars. The exact value will need to be tested on Mars, and will vary significantly if the material is used inside a habitat at Earth atmospheric pressure or outside the habitat at martian atmospheric pressure.

Most insulation is used in assemblies. Structural elements may have high conductivity and decrease thermal resistance. Combination of materials, films and radiation reflective surfaces can modify insulation values significantly.

Table of insulation materials

Material	Thermal conductivity (k) (W/m/C)	Density kg/m3	Embodied energy (MJ/kg)	Heat loss (W/m2)	Notes
Multi layer insulation		45		10-50	This insulation's effectiveness varies with the number of layers. No mechanical strength. Sensitive to convection. 20 to 40 layers.
Foam glass	0,038	160	30?	76	Might be produced in-situ. Relatively high mechanical strength
Fiber glass	0,01 to 0,02	7-12	28	20-40	No mechanical strength
Foams	0,02 to 0,04	20-30	+100	40-80	Might have problems from outgassing. Some mechanical strength
Mineral wool	0,01 to 0,02		17	20-40	No mechanical strength
Aerogel	0,005 to 0,01	16	?	10-20
Vacuum insulated panel	0.007	256		6	50mm panels
Air	0,02	1,2		40	About the same for Mars atmosphere as for Earth
Water	0,6	1000	0,5	1200	Water is not a good insulator
Regolith	0,15-2	1800		300-4000	Depends on compaction and composition
Rock	2-4	1800-2000		4000-8000
Aluminium alloys	50-100	2700		200 000	This is why it is important to minimize themal bridging

The heat loss was calculated for -75C exterior to 25C interior, and a thickness of 50mm.

Basic calculation:

Q=k*A/t*(ti-to) where

Q=Heat loss (Watts) (J/s)

A=Wall area (m2)

t=material thickness (m)

ti-to= temperature difference between interior and exterior (°K)

Tank insulation

Insulation of fuel tanks on Mars may be a requirement to prevent accumulation of frozen CO₂ on tanks. CO₂ freezes a little bellow -67C and could accumulate significant mass on a fuel tank. Tank insulation needs to have a vapor barrier, or be composed of closed cells to avoid the risk of condensation in the insulation and the accumulation of water or CO₂ ice in the material.

Production

Insulation can be produced in-situ. The very low atmospheric pressure of Mars already provides a good insulation, reducing heat transfer from convection.

Foam glass would be an interesting type of insulation to produce on Mars. The resources, mainly silica oxide, are available in large quantities. An adequate foaming agent would need to be identified and mined and the production process refined to create a viable product.

Fiber glass and mineral wool can both be produced in-situ.

Foam can be produced in-situ, however the energy requirements are much higher than for other types of insulation.