Space blanket
Encyclopedia
Blanket
A blanket is a type of bedding, generally speaking, a large piece of cloth, intended to keep the user warm, especially while sleeping. Blankets are distinguished from sheets by their thickness and purpose; the thickest sheet is still thinner than the lightest blanket. Blankets are generally used...
used in emergencies to reduce heat loss in a person's body caused by thermal radiation, water evaporation and convection.
Manufacturing
First developed by NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
in 1964 for the US space program, the material consists of a thin sheet of plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
(often PET film
PET film (biaxially oriented)
BoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
) that is coated with a metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
lic reflecting
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
agent, making it metallized polyethylene terephthalate or MPET, usually gold or silver in color, which reflects up to 97% of radiated
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
heat.
For use in space, polyimide
Polyimide
Polyimide is a polymer of imide monomers. The structure of imide is as shown. Polyimides have been in mass production since 1955...
(e.g. kapton
Kapton
Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -273 to +400 °C...
, UPILEX
UPILEX
Upilex is a heat resistant polyimide film formed from biphenyl tetracarboxylic dianhydride monomers. Its properties include dimensional stability, low water absorption and high chemical resistance...
) substrate is usually employed due to its resistance to the hostile space environment
Corrosion in space
Corrosion in space is the corrosion of materials occurring in outer space. Instead of moisture and oxygen acting as the primary corrosion causes, the materials exposed to outer space are subjected to vacuum, bombardment by ultraviolet light and x-rays, high-energy charged particles...
, large temperature range (cryogenic to 260 °C and for short excursions up to over 480 °C), low outgassing
Outgassing
Outgassing is the release of a gas that was dissolved, trapped, frozen or absorbed in some material. As an example, research has shown how the concentration of carbon dioxide in the Earth's atmosphere has sometimes been linked to ocean outgassing...
(making it suitable for vacuum use
Materials for use in vacuum
Materials for use in vacuum are materials showing very low rate of outgassing in vacuum, and, where applicable, tolerant to the bake-out temperatures. The requirements grow increasingly stringent with the desired degree of vacuum achievable in the vacuum chamber.The materials can produce gas by...
) and resistance to ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
radiation. Aluminized kapton, with foil thickness of 50 and 125 µm, was used e.g. on the Apollo Lunar Module
Apollo Lunar Module
The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman to carry a crew of two from lunar orbit to the surface and back...
. The polyimide gives the foils their distinctive amber-gold color.
In the US, space blankets are made by vacuum depositing
Vacuum deposition
Vacuum deposition is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub-atmospheric pressure on a solid surface. The layers may be as thin as one atom to millimeters thick . There may be multiple layers of different materials...
a very precise amount of pure aluminum vapor onto a very thin, durable film substrate.
Usage
In their principal usage, space blankets are included in many emergency, first aidFirst aid kit
A first aid kit is a collection of supplies and equipment for use in giving first aid, and can put together for the purpose , or purchased complete...
, and survival kits because they are usually waterproof and windproof. That, along with their low weight and ability to pack into a small space, has made them popular among outdoor enthusiasts and emergency workers. Space blankets are often given to marathoners at the end of races. The material may be used in conjunction with conductive insulation material and may be formed into a bag for use as a bivouac sack
Bivouac sack
A bivouac sack is an extremely small, lightweight, waterproof shelter, and an alternative to traditional tent systems. It is used by climbers, mountaineers, hikers, ultralight backpackers, soldiers and minimalist campers...
(survival bag).
In first aid
First aid
First aid is the provision of initial care for an illness or injury. It is usually performed by non-expert, but trained personnel to a sick or injured person until definitive medical treatment can be accessed. Certain self-limiting illnesses or minor injuries may not require further medical care...
the blankets are used to prevent/counter hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...
. A threefold action facilitates this:
- The airtight foil reduces convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
- Heat loss caused by evaporationEvaporationEvaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
of perspiration, moisture or bloodBloodBlood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
is minimized by the same mechanism - To a limited extent the reflectiveReflection (physics)Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
surface inhibits losses caused by thermal radiationThermal radiationThermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
.
In a hot environment they can be used to provide shade, but using them to wrap a person would be counterproductive, because body heat
Body heat
Body Heat is a 1981 film by Lawrence Kasdan.Body Heat may also refer to:*Body heat or thermoregulation, the ability of an organism to keep its body temperature within certain boundaries*Body Heat...
would get trapped by the airtight foil. This effect would exceed any benefit gained from heat reflection to the outside.
Space blankets are used to reduce heat loss from a person's body, but as they are constructed of PET film
PET film (biaxially oriented)
BoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
, they can be used for other applications for which this material is useful, such as insulating containers—e.g. for DIY solar projects—and other applications.
In addition to the space blanket, the United States military also uses a similar blanket called the "casualty blanket". It uses a thermal reflective layer similar to the space blanket, backed by an olive drab colored reinforcing outer layer. It provides greater durability and warmth than a basic space blanket at the cost of greater bulk and weight. It is also used as a partial liner inside the layers of bivy sacks in very cold weather climates.
See also
- Thin-film deposition
- ThermoregulationThermoregulationThermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
- EmissivityEmissivityThe emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...
- Thermal insulationThermal insulationThermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
- Radiant barrierRadiant barrierRadiant barriers or reflective barriers inhibit heat transfer by thermal radiation. Thermal energy may also be transferred via conduction or convection, however, and radiant barriers do not necessarily protect against heat transfer via conduction or convection....
- ReflectivityReflectivityIn optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...
- R-valueR-value (insulation)The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...
- Survival bag