An (Integrated) Thermal Micrometeoroid Garment (TMG or ITMG) is the outer layer of a

space suit A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...

. The TMG has three functions: to insulate the suit occupant and prevent heat loss, to shield the occupant from harmful

solar radiation Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ( ...

, and to protect the astronaut from micrometeoroids and other

orbital debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict space ...

, which could puncture the suit and depressurize it. (This latter function is provided for spacecraft by Micrometeoroid and Orbital Debris (MMOD) Protection systems.) The specific design of TMGs varies between different

space agencies This is a list of government agencies engaged in activities related to outer space and space exploration. As of 2022, 77 different government space agencies are in existence, 16 of which have launch capabilities. Six government space agencie ...

and different suits, though they all serve the same purpose.

A7L suit (Apollo/Skylab)

Outside a Liquid Cooling and Ventilation Garment, pressure bladder, and restraint layer, the TMG for the A7L suit worn on the Moon and during the

Skylab Skylab was the first United States space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three separate three-astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Major operations ...

Program began with a layer of neoprene-coated

nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from pe ...

ripstop __NOTOC__ Ripstop fabrics are woven fabrics, often made of nylon, using a reinforcing technique that makes them more resistant to tearing and ripping. During weaving, stronger (and often thicker) reinforcement yarns are interwoven at regular inte ...

. This was the innermost layer of protection from micrometeoroids. Next,

thermal radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) i ...

protection was provided by five layers of

aluminized Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ...

PET film (

Mylar BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and a ...

), alternating with four layers of

nonwoven Nonwoven fabric is a fabric-like material made from staple fibre (short) and long fibres (continuous long), bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing industry to denote fabri ...

Dacron Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foo ...

, which provided thermal spacing, followed by two layers of aluminized polyimide Kapton film and

Beta cloth Beta cloth is a type of fireproof silica fiber cloth used in the manufacture of Apollo/Skylab A7L space suits, the Apollo Thermal Micrometeoroid Garment, the McDivitt Purse, and in other specialized applications. Beta cloth consists of fine ...

marquisette Marquisette is a lightweight, sheer fabric that has a structure similar to a mosquito net. Construction Marquisette is a very loose weave construction plain and sometimes with designs. Leno is one type of weaving the marquisette. Marquisette ...

laminate. The outermost layer of PTFE (

Teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemo ...

)-coated filament Beta cloth was non-flammable and provided abrasion protection from the notoriously abrasive lunar dust. This layer was supplemented with Teflon abrasion patches at the knees and other areas.

EMU suit (Space Shuttle/ISS)

The construction of the TMG on the

EMU The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus '' Dromaius''. The emu ...

suits in use on the

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program ...

and

International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ( ...

differs somewhat from the construction of the Apollo/Skylab TMG. The EMU TMG includes seven layers of aluminized Mylar laminated with Dacron, rather than five, and eliminates the use of Kapton. The outermost layer is white Ortho-Fabric, made with a blend of

Gore-Tex Gore-Tex is a waterproof, breathable fabric membrane and registered trademark of W. L. Gore & Associates. Invented in 1969, Gore-Tex can repel liquid water while allowing water vapor to pass through and is designed to be a lightweight, waterpr ...

Kevlar Kevlar (para-aramid) is a strong, heat-resistant synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, the high-strength material was first used commercially in the early 1970s a ...

, and

Nomex Nomex is a flame-resistant meta-aramid material developed in the early 1960s by DuPont and first marketed in 1967. Properties Nomex and related aramid polymers are related to nylon, but have aromatic backbones, and hence are more rigid and mo ...

. This layer can withstand temperatures from −300° to +300°

Fahrenheit The Fahrenheit scale () is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined hi ...

(−184.4° to 149° Celsius). The outer layer provides both micrometeoroid and thermal protection, by reflecting most of the sun's thermal radiation.

References

{{Project Skylab Human spaceflight Space suit components