One benefit of a large solar cycle is to clear out some of the
unwanted artificial space debris that is currently circling in low
Earth orbit. At the end of 2001 there were believed to be around
9000 objects larger than 10 cm orbiting the Earth. Of these, only
6 percent are operational satellites. The remainder are old satellites,
rocket bodies, or other fragments. All of them pose a potential impact
hazard to the operational spacecraft.
Ever since the start of the space age in 1957 (when Sputnik I was
launched), the extent of space debris has increased to the point where
there is now a real hazard to large operational structures such as space
stations. The accompany graph show the increase in objects tracked
and catalogued by NORAD each year for the first 3 decades of space
operations.
Of interest here is the dip shown in the years 1979-80. This results
from the increased atmospheric density at satellite altitudes around
the time of the cycle 21 solar maximum. This increase was large enough
to cause the rapid re-entry of many objects in the 200-400 km altitude
range. This was the first time that the attrition rate of space 'junk'
exceeded the generation rate from launch activity and fragmentation of
existing objects in space. A similar and even more pronounced dip
was produced at the maximum of solar cycle 22, around 1990.
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