287 SYSTEMS: EXTRAVEHICULAR ACTIVITIES—BUILDING A SPACE STATION CHAPTER 17 whether the crew member is shaded from direct sunlight, whether the tool or the contact surface tends to absorb or reflect heat, and the crew member’s activity level relative to the cooling system of the suit. Cooling is performed both passively and actively. Passive thermal control and radiation protection is provided by the outer suit layers that reflect sunlight and provide insulation. Active cooling removes generated and absorbed heat via a circulating water system with a component called the sublimator. Tanks supply water to form a sheet of ice on the sublimator, which is exposed to the vacuum of space. In a vacuum, the ice sublimates (i.e., transitions directly from a solid to the gas phase without going through the liquid phase), removing heat as part of the process. Oxygen that is being circulated through the CCC and fan passes through the sublimator to provide cooling of the circulating gas and to condense out excess humidity. Water is circulated over the crew member’s body via the Liquid Cooling and Ventilation Garment (LCVG), which is an internal bodysuit with approximately 91 m (300 ft) of thin flexible tubing sewn into the fabric. Ventilation ducting provides oxygen circulation in the arms and legs of the suit, thus the gas in those areas is also cleansed and dehumidified (Figure 7). Figure 7. An LCVG, with its small water-filled tubes throughout and larger yellow ventilation ducts on the shoulders, floats in the airlock. The water tubes and ventilation ducting come together at the right waist with a connection point to the spacesuit. The fan/pump/water separator in the suit’s backpack (not shown) provides the circulation. Shoulder pads provide a cushion from hard points in the suit and help fill some volume for an overall snug and comfortable fit. In addition to providing thermal control, the carefully crafted multiple- layer composition of the suit is a stack of nylon, insulation, and fabric. Its design holds in the pressure, restrains the suit to conform to the body, and provides some protection from suit leaks due to small MMOD hits or punctures from tools or sharp objects on the ISS. The outer garment protects the internal pressure bladder (i.e., coated nylon “balloon” that keeps the pressure in) with materials that help protect against abrasion, puncture, and damage propagation. In other words, the design intention is such that a small hole is less likely to become a huge rip as the crew member moves around in the suit. Communication with other spacewalkers, the ISS, and the ground occurs through an ultra-high frequency (UHF) radio system, at a frequency that is lower than that used in car alarm systems and walkie-talkies (see Chapter 13). UHF antennas are located in the airlock and on the outside of the space station to transmit communication and some EMU status information to the ISS. That information is relayed to the ground through the standard space station communication system. Each EMU has a primary radio and a backup radio (as does the UHF system