49 SYSTEMS: STRUCTURE AND MECHANISMS—THE INTERNATIONAL SPACE STATION’S SKELETON CHAPTER 3 Some debris with higher energy will penetrate the shielding. The debris will lose energy and fracture into multiple smaller pieces. These pieces will travel through the insulation material, which will cause the debris fragments to continue to lose energy and spread out from the point of penetration. Debris that started smaller than 1 cm will either not make it to the primary pressure shell, or will strike the pressure shell but not penetrate. Other areas of the ISS where the likelihood of debris strikes and penetration are lower, or areas that are not habitable by the crew, may be protected only by thick insulating blankets. This is true for many areas of the Russian Segment, especially the shorter-duration Soyuz and Progress vehicles. For this shielding, the blanket properties and thickness are such that the debris will be stopped prior to penetrating the pressure shell. Hatches As mentioned previously, one of the larger feedthroughs in any module is the hatchway. These hatchways enable crew and cargo to pass between modules. Each module has a hatch to close off each hatchway vestibule for each module to remain pressurized before it is attached to the ISS, and to allow for the isolation of the modules in the event of a depressurization or contaminated atmosphere. The US Common Hatches are 1.2 m (50 in.) square in size (Figures 16 and 17). The hatch system is designed such that when the hatch is closed, the force of the internal module air pressure pushes the hatch against the bulkhead seals of the module and provides the sealing force. Latches are included on the hatches, but these latches are only needed to ensure the hatch is aligned with the bulkhead and pulled close enough to the module such that the air pressure can provide the sealing force. The latch mechanisms also have a component called a “kicker” that pushes against the module bulkhead when the hatch is unlatched to help push the hatch off the bulkhead. Figure 16. The smooth internal side of a US Common Hatch. This side faces into each module. Note the handle in the center right that the crew turns to latch or unlatch the hatch, a deployable handle at the bottom center to engage or release the hatch from its stowed position, a valve in the bottom right corner of the hatch used to equalize the pressure between the two sides of the hatch prior to opening the hatch, and a window in the center of the hatch. The round hatches of the Russian Segment modules are 80 cm (31.5 in.) in diameter. This includes the hatches between module vestibules as well as hatches between modules and docked vehicles (i.e., Progress, Soyuz, or Automated Transfer Vehicle). The hatches on PMAs 1, 2, and 3 are also 80 cm (31.5 in.) in diameter, based on the Russian hatch design. Additional hatches on the ISS include the inner and outer hatches on the Japanese Airlock and the outer egress hatch of the Joint Airlock. The EV (for extravehicular) hatch on the Joint Airlock is the same Shuttle B-type hatch that was found on the airlock of the orbiter. This is due to the fact that the Crewlock portion of the Joint Airlock is actually an exact duplicate