DON’T call these relics ‘space junk’! 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 example, the Apollo astronauts couldn’t clean up the ALSEP sites and bring back home all the packaging (see picture below, credit: NASA): if they had done so it would have been at the expense of the precious lunar rocks and their very short time on the surface doing science. Unfortunately, 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:

  • Group 1, ‘visual annoyance’ (surface): inert items, such as aluminum parts or soft bags, which have no impact on the environment (see the Apollo 17’s ALSEP site in the picture below, credit: NASA);
  • Group 2, ‘NBCs’ (surface): Nuclear, Biological or Chemical active items (e.g. RTGs, spacecraft batteries or propellant tanks) that can induce pollution or contamination in probable organic or icy worlds such as Venus, Mars, Gas Giants’ Moons, dwarf planets, comets and some asteroids;
  • Group 3a, ‘hazardous objects’ (orbit): hyper-velocity items travelling throughout the solar system, posing a threat to space navigation and to the surface of celestial bodies;
  • Group 3b, ‘hazardous objects’ (surface): debris or loose hardware that may pose as a risk of entanglement to the Rovers.

While all cases should be remediated, both groups 2 and 3a must be emphasized to mitigate consequences. This catalogue is a step in this direction.