Anthonares

In an analysis published yesterday in Science magazine, two NASA scientists report that the threat of space junk will steadily increase even if no new satellites or rockets are launched [citation]. We have reached a critical threshold at which the density of debris and junk at certain altitudes is high enough to guarantee collisions resulting in many more debris fragments. What’s more, by 2050 (again without launching anything new), the number of new debris fragments created each year by collisions will outnumber those whose orbits decay and fall back to the Earth. In fewer than 50 years we have managed to create a self-sustaining, semi-permanent cloud of orbital “pollution” that threatens all future commercial and exploration activities within certain altitude ranges.

Those altitude ranges just happen to be the commercially, militarily, and scientifically valuable 600-1000 km and 1400-1500 km windows. GPS, spy satellites, weather satellites, and other polar-orbiting satellites commonly orbit at these altitudes. It’s not as if other altitude ranges can be selected arbitrarily; if one desires the orbital period of the satellite to be sun synchronous, observing the same place on the globe at the same time of day every day, the altitude must be between 600-800 km.

The debris clouds we’ve created in these two shells surrounding the Earth by no means form a prison through which we cannot pass; the danger in those areas falls mainly on the satellites or facilities that have orbits there. In fact, the clouds of debris would be all but invisible to human eyes because of the sheer vastness of orbital space. The image on the left (credit: NASA) shows the low-earth orbit (LEO) debris cloud as is being tracked by the NASA Debris Office.

The authors of the Science policy paper cited above go on to discuss the options we have for preventing this steady build-up. Proposed ideas, summarized nicely over at Wikipedia, include attaching ion engines or electromagnetic drag-inducing tethers, robotic tug removal, vaporization or perturbation with ground-based lasers, and even placing large chunks of aerogel in orbit that would deorbit much more quickly than the smaller debris would. However, at this point none of these options are both proven and economically viable.

The authors note that there are 5 million kg (5 thousand metric tons) of material up there. Though they do not discuss this option, there may be significant salvage value of so much scrap iron in orbit. So, the use of graveyard orbits for later salvage may become much more commonplace as we enter a true age of commercialization of space.

Innovation is needed to solve this problem and retain the use of the invaluable LEO altitudes, and a combination of manual deorbiting and graveyard orbit salvage will probably be the most doable. It is possible that, in a generation or so, the business of orbital cleanup will be profitable given that the operation would get rights to whatever it salvages. So, the profits from selling already on-orbit materials may pay for the cost of getting rid of the worthless chips of paint or metal that populate those orbits in the millions.