A big talking point at NSS this year was the growing issue of space debris and the need for additional space situational awareness. According to figures about debris discussed by a panel at the symposium, there are between 19,000 and 20,000 objects larger than 10 cm (4 in) in orbit, plus 500,000 objects 1 to 10 cm in diameter, and tens of millions of smaller particles.
Current technology enables observation of debris as small as around 5 mm (0.2 in) in LEO, however only objects larger than 10 cms are tracked because it is next to impossible to predict the trajectories of smaller objects accurately.
While the 2007 Chinese anti-satellite test and 2009 Iridium-collision raised most eyes spaceward, others have also begun to study the prospect for more space junk coming back down in one–piece. The Aerospace Corporation’s Center for Orbital and Reentry Debris Studies has identified 60 pieces of space debris found throughout the world from 1960 to 2008. Although there is only one recorded instance of a human being impacted by a piece of known man-made space debris (a certain Lottie Williams, received a shoulder injury from a piece of metal mesh – believed to be from a Delta II - while walking in a park in Tulsa, Okla.), the study shows the statistics for a future impact are obviously trending upward.
Its analysis shows that significant pieces of random debris, in excess of 5 square meters, have impacted a landmass of the earth. For this size of debris the risk to the public approaches 100 in a million when considering the year 2005 world population and exceeds 100 in a million when considering a world population expanded to the year 2050.
This Delta II titanium pressure vessel survived re-entry intact. (Guy Norris)
The worst offenders, in terms of ability to survive re-entry relatively intact, appear to be titanium spherical pressure vessels used for pressurized fuels. So the message is clear – keep watching the skies!