File:ISS Micrometeoroid and Orbital Debris (MMOD) Protection.svg

English: Micrometeoroid and Orbital Debris (MMOD) Protection

Spacecraft in low-Earth orbit are continually impacted by meteoroids and orbital debris. Most of the meteoroids and debris are small and cause little damage. A small fraction of the meteoroid and debris populations, however, are larger and can cause severe damage in a collision with a spacecraft.

The International Space Station (ISS) is the largest spacecraft ever built. With the completion of assembly more than 11,000m2 (118,400 ft2) of surface area is exposed to the space environment. Due to its large surface area, its long planned lifetime, and the potential for a catastrophic outcome of a collision, protecting the ISS from meteoroids and debris poses a unique challenge. Many ISS elements are shielded from impacts. The primary shielding configurations are:

• Whipple shield is a two layer shield consisting of an outer bumper, usually aluminum, spaced some distance from the module pressure shell wall; the bumper plate is intended to break up, melt, or vaporize a particle on impact. This type of shield is used where few MMOD impacts are expected (aft, nadir and zenith areas of ISS.)
• Stuffed Whipple shield consists of an outer bumper, an underlying blanket of Nextel ceramic cloth, and Kevlar fabric to further disrupt and disperse the impactor spaced a distance from the module pressure shell. Because these shields have a higher capability than Whipple shields, they are used where more MMOD impacts are expected to occur (front and starboard/port sides of ISS).

Windows are generally multi-pane with separate and redundant pressure panes, as well as an outer debris pane and/or shutter to provide protection from MMOD. Other critical areas, such as electrical, data, and fluid lines on the truss and radiator panels, are toughened with additional protective layers to prevent loss from MMOD impacts.