Before calling these relics ‘space junk’, it must be remembered that mass and space exploration are not compatible: a spacecraft can’t afford trailing unnecessary load, so items that are no more useful at one point into the mission become dead weight and must be shaved off quickly. For instance, the Apollo astronauts couldn’t come back home with all the spent ALSEP deployment hardware; if they had done so it would have been at the expense of the precious lunar rocks. As of today, there is no other viable option to guarantee mission success and there are no means to retrieve them.
Thus, ‘derelict objects’ is a more appropriate word to qualify them and they can be classified into three groups:
While all cases should be remediated, both latter groups must be emphasized to mitigate consequences. This catalogue is a step in this direction.