Q 3.3 What is orbital debris and how are they tracked?

There are a number of specialized dedicated systems for tracking useless pieces of natural space objects such as meteorites and man-made objects like defunct satellites, expended parts of launchers, pieces of exploded satellites, etc. Man-made debris is also known as space junk. Space debris poses a collision risk to other space objects. Although probability of such occurrences is at present small, collisions have been reported. There is thus a growing concern about long term detrimental effects of space junk since number of useless space objects continues to increase. Beginning at zero level at the dawn of space era in 1957, number of discernible objects from the Earth has increased to nearly 15000 by the year 2010 according to a UN study.
Ground-based space debris measurements utilise radars and optical systems like telescopes, depending on the altitude of interest. Space-based measurements utilize satellites and sensors built specially to assess the effects and statistics of orbital debris.

UN, (1999) ‘Technical Report on Space Debris’, United Nations Publication, Sales No. E.99.I.17 ISBN 92-1-100813-1.
NASA, (2010) ‘Orbital Debris Quarterly News’, Volume 14, Issue 1, January.