Monitoring the low earth orbit debris environment over an 11-year solar cycle

Orbital debris is a concern for all space faring nations. Prior to 1990, there were no statistically significant measurements of the debris environment for debris sizes below 10 cm diameter. Late in that year, NASA/Johnson Space Center began using the Haystack long range imaging radar to statistically sample the low earth orbit (LEO) debris environment for debris sizes as small as 0.5 cm diameter. These measurements have continued since that date. Models of the LEO debris environment predict a change in the debris flux due to solar activity. High solar activity heats the earth's atmosphere causing it to expand creating an increased atmospheric drag which causes debris to reenter the earth's atmosphere at a higher rate thereby depleting the population at low altitudes. This paper will summarize the Haystack measurements over a complete 11-year solar cycle.