The 2013 space thriller film Gravity, in which two astronauts become stranded in space after a cloud of fragments from an exploded satellite destroys their space shuttle, vividly depicts one of the major issues impacting on current and future space activities – the problem of “space junk”, or orbital debris.
Technically defined as “all man-made objects in orbit about the Earth which no longer serve a useful purpose” (NASA Orbital Debris FAQ at http://www.orbitaldebris.jsc.nasa.gov/faqs.html), orbital debris has been created in many ways and is composed of such items as inactive satellites and other pieces of abandoned or derelict space hardware and spent launch vehicle upper stages that attained orbit. Mission-related debris includes multiple vehicle carriers (used for launching several satellites from the same rocket), reactor fuel cores from radar satellites, refuse from crewed missions, and tools and equipment that have broken off from spacecraft or floated away through open hatches (including nuts, bolts, hand tools and the odd spacesuit glove).
The largest category of space junk is fragmentation debris, shrapnel-like pieces of exploded satellites and rocket stages. This type of debris commonly results from the explosion of residual fuels...
