Micrometeorites seen with a scanning electron microscope (From CRREL)
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Micrometeorites seen with a scanning electron microscope (From CRREL)
Micrometeorites are pieces of rock less than 1 mm in diameter (comparable to the size of fine grains of sand) traveling at speeds up to 80 km per second (48 miles per second). As such, they are extremely difficult to detect and even if they could be detected there is no practical way to avoid them.
The high speed of the micrometeorites are what make them dangerous. Their mass is small, but their high velocities give them enormous energy (Kinetic Energy = 0.5 * mass * velocity^2). So they can damage or even penetrate spacecraft. Fortunately space is relatively empty, so at any given time the threat of a micrometeorite impact is low. However, for the International Space Station which has a designed lifetime of 30 years, the probability that it will receive a micrometeorite impact during its mission approaches a certainty.
Since micrometeorites cannot be avoided, spacecraft and space suits are designed to protect crew members when the micrometeortites strike. Current space suits for example use Gortex, Kevlar (the same material used in bulletproof vests) and Nomex to protect an astronaut during a spacewalk.
In general, the materials used for the hull of a spacecraft are adequate for protecting the crew against micrometeorites. Impacts have been recorded on the space shuttle and other spacecraft. There have also been several experiments over the history of the space program to look at micrometeorite impacts. Examples would be experiments on Gemini 8 and LDEF. None have punctured the hull of a manned spacecraft.
For large sytems such as solar panels and radiators, the number of micrometeorite impacts over the life of the structure can be estimated based on prior experience. The system is then designed to lose a certain portion of itself to micormeteorite impacts over the life of the system and still provide all the capability needed for the mission. For example, the International Space Station will have extra photovoltaic cells in each solar panel. If one cell or group of cells is damaged, the total power of the panel is reduced, but the panel will continue to provide power. Enough extra cells are in the panels to ensure plenty of power up to the point where the panels will be replaced.
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