People used to toss Styrofoam containers and cups on the side of the road. Then we learned that polystyrene foam takes an epoch to degrade, so we switched to paper products. But we threw that stuff on the ground anyway. It mixed with old tires, used diapers, garbage bags, mufflers, cans, condoms, cigarette butts, and pieces of tail lights. The collective dishevelment would horrify all our mothers. Now, like our roads and bedrooms, Earth’s orbit is a major dump.
Orbital debris takes the form of dead satellites, jettisoned modules, specks of paint, shrapnel from collisions, rocket fuel, and pieces of junk too small to register. Using a variety of methods and instruments, the NASA Orbital Debris program office has kept a tally:
- There are 21,000 pieces of orbital debris larger than 10 centimeters.
- There might be 500,000 pieces between one and ten centimeters,
- Particulate matter smaller than 1 cm. in size exceeds 100 million.
Think of all that junk swirling around on the surface of a swimming pool. Then imagine a vehicle trying to function within this moving cloud of flotsam. Space is already a dangerous environment without fender benders! NASA has replaced windows on the space shuttle before, and the International Space Station, Mir, and the Hubble Space Telescope have also seen their share of dents and scrapes. The primary cause behind orbital debris is pretty scary:
Prior to 2007, the principal source of debris was from explosions of old launch vehicle upper stages left in orbit with stored energy sources, e.g., residual propellants and high pressure fluids. The intentional destruction of the Fengyun-1C weather satellite by China in 2007 and the accidental collision of American and Russian communications satellites in 2009 greatly increased the number of large debris in orbit and now represent one-third of all cataloged orbital debris.
When you also learn that the average impact velocity of one piece of debris hitting another is approximately 10 kilometers per second, you think about crawling under your bed. Luckily, NASA doesn’t shy away from a challenge. The agency has looked at everything from lasers to tugs in an effort to clean up orbit. Orbital debris can be further reduced if spacecraft jettison fewer parts or burn up in the atmosphere at the end of their service lifetimes. Committing to a debris-capture mission, hopefully within budget limits, can also reduce our collection of junk:
ADR [active debris removal] techniques need to concentrate on the removal of large, massive objects such as intact rocket bodies and non-functional satellites. These massive objects are the long-term source of fragmentation debris from on-orbit explosions and collisions. Studies have indicated that the removal of as few as five of the highest risk objects (defined as mass x probability of collision) per year can stabilize the long-term low Earth orbit debris environment.
So if astronauts manage to clean out a handful of antique boosters or solar panels, Earth’s orbit will be a safer place for all travelers. The work won’t happen overnight (very likely a constant activity in the future of organized space flight) and the combined efforts of many agencies and specialists will be required. Soon enough, we’ll get around to cleaning up our room! Mom would be proud.