In 1958, the Vanguard I satellite was the fourth satellite launched into orbit; with its inactivation thirty-three years later, it also became the oldest piece of human debris in space. Debris has been accumulating ever since, and after fifty years of space exploration, the final frontier has already become littered. Currently NASA is looking at ways to mitigate space litter to lessen its potential threat on future space efforts.
“The current threat is that we will start to lose the things which we value in space,” said Prof. Joseph Burns, aerospace engineering and astronomy. “The world has become very reliant on space infrastructure for global communications, surveillance, and weather satellites—all of which will be jeopardized if we cannot control space debris.” Burns also served as NASA adviser during its Cassini mission, which orbited around Saturn.
Space debris are non-functional human-made objects currently in orbit around the Earth. They can vary in size, from large discarded rocket stages and defunct satellites to small nuts, bolts and satellite fragments. Orbital debris like these are found in two different layers outside of the Earth’s atmosphere: Low-earth orbit and geostationary-earth orbit.
Low-Earth orbit typically encompasses the area extending 160 to 2,000 kilometers above the Earth’s surface. At this altitude, atmospheric drag has an effect on orbital debris, so some large objects are brought to crash down on the Earth, and other smaller objects burn up in the atmosphere. NASA reported that 73 percent of all tracked space debris is in the LEO, the rest occur in the higher altitude geosynchronous-earth orbit region, where satellites are typically found.
The majority of space debris floating in these levels is small, about 4 inches or less. Despite their size, these small debris are devastating in orbit. In 1983, a small paint flake struck the space shuttle Challenger - punching a small crater into the shuttle’s window resulting in $50,000 of damage.
“Because these particles are orbiting the Earth, they are moving at about 5 miles a second,” Burns said. “And when things collide at 5 miles a second, they essentially blow up whatever they hit.”
In order to remain in orbit, many fragments have to travel at 20 times the speed of sound which amounts to almost 18,000 miles per hour. In fact, traveling at this speed, a cherry-sized piece of space debris can strike with the force of a hand grenade and debris one thirty-fifth the size of an aspirin can create the same impact as a .30 caliber bullet.
In 2007 the Chinese military intentionally exploded its own satellite, the Fengyun 1-C, sending about 3,000 pieces of debris into orbit. Pieces from the explosion now encircle the earth. China produces the most space junk of any nation and the Fengyn 1-C explosion alone raised the amount of global orbiting debris by ten percent.
China is not the only culprit contributing to the ring of debris; the United States and Russia rank second and third, respectively in space junk production. One particular space debris catastrophe involving both nations occurred in 2009 when Iridium 33, a U.S phone satellite, and Cosmos 2251, a long-retired Russian satellite, slammed into each other mid-orbit spewing about 2,000 pieces of debris according to NASA. Six months after the explosion, NASA had to maneuver its Terra satellite away from oncoming debris from the Fengyun 1-C, which would come within 19 meters of hitting it.
The two events generated the worst satellite fragmentation of the space age and together account for 36 percent of the total number of cataloged space debris orbiting in low-Earth orbit. “What people are fearful of is that we may be reaching the tipping point where there is so much space debris up there that the collisions will make this a self-sustaining process,” said Burns.
The hazards that space junk pose towards satellites and space stations have prompted the creation of the NASA Orbital Debris Program Office, which is NASA’s leading center in orbital debris research. “Currently NASA’s active work is in preventing further space debris and coming up with mitigation techniques,” said Burns.
In September of this year the National Research Council published a 180-page report on NASA’s efforts to mitigate the risk posed by meteoroid and space debris. The council recommended that more funds be allocated to maturing meteoroid and orbital debris programs and that NASA improve its long-term debris modeling system and measurement equipment. Although there are international guidelines concerning the reduction of space debris, the question of who is responsible for developing the clean up process still remains.
“It’s not easy to get rid of this stuff, you’ve got tens of thousands of objects in the sky and you can’t readily go and sweep them up,” said Burns.
As of now, the U.S Space Surveillance Network has already detected over 21,000 objects larger than 10 centimeters (4 inches) in low-Earth orbit. But it is estimated that there are over 500,000 objects less than one centimeter around the size of a marble in orbit and another tens of millions of paint-chip like pieces smaller than a centimeter as well. Ideas proposed at the International Conference on Orbital Debris Removal to clean up the space debris mess include net-throwing nanosatellites, large spacecraft nets, and electrodynamics space kites.