In a few weeks, according to news reports, the International Space Station will have a new little buddy – China's Tiangong I, an unmanned 8.5-ton space lab designed to function as a test bed for a future 60-ton lab destined for launch around 2020. Elsewhere, Russia's Orbital Technology has unveiled plans to open up a space hotel by 2016. Meanwhile, Euroconsult estimates that more than 1,200 satellites will go into orbit between now and 2019.
It's going to start getting crowded up there.
Actually, it already is. According to NASA, some 19,000 pieces of space junk more than 10 cm in diameter are merrily circling the earth, the bulk of them in orbital altitudes ranging from 800 to 850 km. Narrow the window to between 1 cm and 10 cm, and the number jumps to 500,000. Sources range from decommissioned spacecraft and discarded launch stages to debris generated by explosions or collisions. Of course, where it comes from hardly matters – the problem is that it's not going anywhere. At altitudes around 600 km, objects might fall to Earth within a few years, but at the 800 km point, debris will remain stable for decades. Jump up to 1,000 km, and it will be there for a century or more – a century during which space travel will most likely become routine, if not commonplace.
Figure 1: NASA simulation provides an idea of just how crowded the neighborhood has gotten. (Courtesy of NASA)
Aesthetics aside, orbital debris can present a significant hazard to satellites and vehicles alike. NASA estimates the relative speed of impact between two objects in orbit to be roughly 10 km/s. Debris shields might protect against centimeter-size objects, but the larger the pieces are, the more kinetic energy they carry. The probability of impact between objects larger than 10 cm is characterized as low, but part of the reason the 800 to 850 km range is so crowded is because of a 2009 impact between Russian and U.S. satellites.
Granted, there are moves underway to address the problem. NASA has a sophisticated debris tracking project to ensure manned or other high-value spacecraft can perform evasive maneuvers in the event that they are threatened by a large object. Space agencies around the globe have teamed to form the Inter-Agency Space Debris Coordination Committee (IADC), which works to alter manufacturing and deployment with an eye toward minimizing the generation of new debris.
Figure 2: Orbital debris punched this roughly 0.7-mm-diameter hole in a panel of the Solar Max experiment. (Courtesy of NASA)
Still, there's no real way to clean things up outside of waiting for orbits to degrade. And If space tourism truly takes off (pardon the pun), the probability of impact between debris and a manned vehicle will only increase. Any idea how we can handle this situation?