An (Integrated)Thermal Micrometeoroid Garment (TMG orITMG) is the outer layer of aspace suit. The TMG has three functions: to insulate the suit occupant and prevent heat loss, to shield the occupant from harmfulsolar radiation, and to protect the astronaut frommicrometeoroids and otherorbital debris, which could puncture the suit and depressurize it. (This latter function is provided for spacecraft by Micrometeoroid and Orbital Debris (MMOD) Protection systems.[1])
The specific design of TMGs varies between differentspace agencies and different suits, though they all serve the same purpose.
Outside aLiquid Cooling and Ventilation Garment, pressure bladder, and restraint layer, the TMG for theA7L suit worn on the Moon and during theSkylab Program began with a layer ofneoprene-coatednylonripstop. This was the innermost layer of protection from micrometeoroids. Next,thermal radiation protection was provided by five layers ofaluminizedPET film (Mylar), alternating with four layers ofnonwovenDacron, which provided thermal spacing, followed by two layers of aluminizedpolyimideKapton film andBeta clothmarquisette laminate. The outermost layer ofPTFE (Teflon)-coated filament Beta cloth was non-flammable and providedabrasion protection from the notoriously abrasivelunar dust. This layer was supplemented with Teflon abrasion patches at the knees and other areas.[2]
The construction of the TMG on theEMU suits in use on theSpace Shuttle andInternational Space Station 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 ofGore-Tex,Kevlar, andNomex. This layer can withstand temperatures from −300 to 300 °F (−180 to 150 °C). The outer layer provides both micrometeoroid and thermal protection, by reflecting most of the sun's thermal radiation.
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