question: Why are the helmets of an astronauts reflective?
comment: The Sun is **very bright** in space. Too bright for the austronaut's eyes. Helmets have a reflective shield to cut out about 2/3 of the light. The shield can be stowed, so they can see when in the shadow of Earth, but pictures aren't taken in the dark much, so you usually see it deployed in photos.
passages: Section::::Applications.:Textiles.
  
  Since the 1970s, sheets of metalized polyester called space blankets have been commercially available as a means to prevent hypothermia and other cold weather injuries. Because of their durability and light weight, these blankets are popular for survival and first aid applications. Swarms of people can be seen draped in reflective metalized film after a marathon, especially where the temperatures are particularly cold, like during the annual New York City Marathon which takes place in the fall.
  
  Section::::Applications.:Window treatments.
   These low "E" coatings were originally developed in 1978 at the Solar Energy Corporation (SOLEC) in Princeton, New Jersey for use in tubular evacuated solar collectors. The developer, Robert Aresty, designed them to be used as low emissivity surfaces 
   Section::::History.:Fresnel and the phase shift.
   Retro-reflective materials, in the form of fixed reflectors, reflective tape, and reflective clothing, are useful in making a cyclist visible to other road users. Reflective materials can be applied to bike, rider, or luggage; also, tires are available with reflective sidewalls. Reflectives are visible only when in the beam of a headlight, and even then only within a narrow locus. Importantly, they "do nothing to light up the road". Reflectors are "not" a substitute for lights, but are an important supplement to portable lighting.
  
  Section::::Supplementary lighting and visibility.:Reflective and high-visibility materials.:On the bike.
   The effect is used in satellites and spacecraft to reduce temperature differences caused by direct sunlight on one side of a craft by dissipating the heat over the cold shaded side, where it is dissipated as thermal radiation to space. Since 1961, some unmanned spacecraft (including the Curiosity Mars rover) utilize radioisotope thermoelectric generators (RTGs) that convert thermal energy into electrical energy using the Seebeck effect. The devices can last several decades, as they are fueled by the decay of high-energy radioactive materials.
   Safety reflectors are based from the way raccoons eyes work when light such as from a headlight hits their eyes and reflect back.
   Today’s windshields are a safety device just like seatbelts and airbags. The urethane sealant is protected from UV in sunlight by a band of dark dots around the edge of the windshield. The darkened edge transitions to the clear windshield with smaller dots to minimize thermal stress in manufacturing. The same band of darkened dots is often expanded around the rearview mirror to act as a sunshade.
  
  Section::::Other aspects.
   The rotating actuator used to move the glass cover plate away from the solar cell marked the first use of a multi-cycle shape memory alloy in a space application.
  
  Section::::Results.
   The technology was considered declassified and released to the public in 1996. It is then up to the world marketplace to take the work of NASA scientists and researchers, and develop products from that point. Since 1976, NASA has featured between 40 and 50 commercial products which have benefited mankind worldwide as a result of NASA Technology in their annual premiere publication Spinoff Magazine. In 2003, after exhaustive research into how their technology was utilized, NASA selected the original 'Spinoff' industry leader.
  
  Section::::See also.
  
  BULLET::::- Passive cooling
  
  BULLET::::- Radiant barrier
  
  BULLET::::- Reflective surfaces (geoengineering)
  
  Section::::External links.
   Section::::Use in the space program.
  
  The areas of the space shuttle that have the highest heat loading due to friction upon the shuttle's re-entry with the earth's atmosphere are coated with a black carbon material which emits over 90% of the friction-induced heat that the shuttle experiences upon re-entry.
  
  Although the ceramic technology was developed by NASA, no one has worked "with" NASA in developing products of this type or their associated coatings. Any statements to the contrary are merely marketing and misleading.
   In first aid, the blankets are used to prevent/counter hypothermia. A threefold action facilitates this:
  
  BULLET::::- The airtight foil reduces convection
  
  BULLET::::- Heat loss caused by evaporation of perspiration is reduced
  
  BULLET::::- To a limited extent the reflective surface inhibits losses caused by thermal radiation.
  
  In a hot environment they can be used to provide shade or provide protection against radiated heat, but using them to wrap a person would be counterproductive, because body heat would get trapped by the airtight foil. This effect would exceed any benefit gained from heat reflection to the outside.
   Section::::Types.:Moth eye.
   Different materials resist corrosion in space differently. For example, aluminium is slowly eroded by atomic oxygen, while gold and platinum are highly corrosion-resistant. Gold-coated foils and thin layers of gold on exposed surfaces are therefore used to protect the spacecraft from the harsh environment. Thin layers of silicon dioxide deposited on the surfaces can also protect metals from the effects of atomic oxygen; e.g., the Starshine 3 satellite aluminium front mirrors were protected that way. However, the protective layers are subject to erosion by micrometeorites.
   The whole lower surface of the lifting-body was protected from the heat of re-entry by Toughened Unipiece Fibrous Insulation (TUFI) tiles, a tougher, more impact-resistant version of the Shuttle's HRSI tiles; the upgraded TUFI tiles came into use in 1996. These tiles, matt black like those on the Shuttle, were bonded directly to a multi-piece titanium heat-resistant skin mounted on the aluminium frames.
   Coatings are the simplest and least expensive of the TCS techniques. A coating may be paint or a more sophisticated chemical applied to the surfaces of the spacecraft to lower or increase heat transfer. The characteristics of the type of coating depends on their absorptivity, emissivity, transparency, and reflectivity. The main disadvantage of coating is that it degrades quickly due to the operating environment.
  
  Section::::Current Technologies.:Multilayer Insulation (MLI).
   Provide normal impact resistance, optical quality, heat resistance and good chemical resistance.
  
  Section::::Manufacturing.
   A radiatively cooled TPS for an entry vehicle is often called a "hot-metal TPS". Early TPS designs for the Space Shuttle called for a hot-metal TPS based upon a nickel superalloy (dubbed René 41) and titanium shingles. This Shuttle TPS concept was rejected, because it was believed a silica-tile-based TPS would involve lower development and manufacturing costs. A nickel superalloy-shingle TPS was again proposed for the unsuccessful X-33 single-stage-to-orbit (SSTO) prototype.
   Since the module names are also the names of three of the four Teenage Mutant Ninja Turtles, the NASA MPLM Group approached Mirage Studios (Teenage Mutant Ninja Turtles) artist A.C. Farley to design a logo with a ninja turtle in an astronaut flight suit. There were cloisonné pins produced, as well as stickers and embroidered patches. There are supposed to be mission jackets using this design as well. Because the Ninja Turtles are copyrighted by Mirage Studios, NASA gave Mirage the copyright to the logo in exchange for the use of the studio's character on it.
  
  Section::::Specifications.
   Section::::Manufacturing.
  
  First developed by NASAs Marshall Space Flight Center in 1964 for the US space program,
  
  the material consists of a thin sheet of plastic (often PET film) that is coated with a metallic reflecting agent, making it metallized polyethylene terephthalate (MPET), usually gold or silver in colour, which reflects up to 97% of radiated heat.
   Section::::Components.:Reflective layer.
  
  The reflective layer is designed to reflect the maximum amount of solar energy incident upon it, back through the glass substrate. The layer comprises a highly reflective thin metal film, usually either silver or aluminum, but occasionally other metals. Because of sensitivity to abrasion and corrosion, the metal layer is usually protected by the (glass) substrate on top, and the bottom may be covered with a protective coating, such as a copper layer and varnish.
   Section::::Promotional programs.:Cool Roofs Europe and other countries.
  
  This project is co-financed by the European Union in the framework of the Intelligent Energy Europe Programme.
   Metallised PET films are used in NASA spacesuits to reflect heat radiation, keeping astronauts warm, and in ″proximity suits″ used by firefighters for protection from the high amount of heat released from fuel fires. Aluminized emergency blankets are also used to conserve a shock victim's body heat. MPET has been used as an antistatic container for other heat and sound insulating materials used in aircraft, to prevent the insulation from leaking into the passenger cabin, but is not itself the insulator in that use.
  
  Section::::Uses.:Electronics.
   Additionally, the ITMG also used a patch of 'Chromel-R' woven nickel-chrome (the familiar silver-colored patch seen especially on the suits worn by the Apollo 11 crew) for abrasion protection from the Portable Life Support System (PLSS) backpack. Chromel-R was also used on the uppers of the lunar boots and on the EVA gloves. Finally, patches of Teflon were used for additional abrasion protection on the knees, waist and shoulders of the ITMG.
   Multilayer insulation (MLI) is the most common passive thermal control element used on spacecrafts. MLI prevent both heat losses to the environment and excessive heating from the environment. Spacecraft components such as propellant tanks, propellant lines, batteries, and solid rocket motors are also covered in MLI blankets to maintain ideal operating temperature. MLI consist of an outer cover layer, interior layer, and an inner cover layer. The outer cover layer needs to be opaque to sunlight, generate a low amount of particulate contaminates, and be able to survive in the environment and temperature to which the spacecraft will be exposed. Some common materials used for the outer layer are fiberglass woven cloth impregnated with PTFE Teflon, PVF reinforced with Nomex bonded with polyester adhesive, and FEP Teflon. The general requirement for the interior layer is that it needs to have a low emittance. The most commonly used material for this layer is Mylar that is aluminized on one or both sides. The interior layers are usually thin compared to the outer layer to save weight and are perforated to aid in venting trapped air during launch. The inner cover faces the spacecraft hardware and is used to protect the thin interior layers. Inner covers are often not aluminized in order to prevent electrical shorts. Some materials used for the inner covers are Dacron and Nomex Netting. Mylar is not used because of flammability concerns. MLI blankets are an important element of the thermal control system.
   According to the US DOE's "Guidelines for Selecting Cool Roofs" on the subject of cool roof maintenance:
  