Orbital Space Debris
The sun rose blindingly over the crest of the earth. The astronaut moved outside the Space Shuttle Discovery’s cargo bay in his Manned Maneuvering Unit (MMU). Held by the shuttle’s robotic arm, a damaged satellite hung about 800 kilometers above the earth and a few meters below the astronaut. As the space walker hovered closer to the satellite, he looked down to see clouds covering parts of America, including his home state of Nebraska. The satellite was damaged badly. Sporting only one solar panel, it had a broken metal arm that made merely a stub on the other side. The day earlier, they had intercepted the missing solar panel, burned and smashed beyond repair. Upon inspection of the damages, both in space and back on earth where the satellite was taken, it was confirmed that a small piece of foreign space debris was responsible for knocking out this civilian communications satellite. While in the vastness of space, an accident like this seems only realistic in a Hollywood movie, but this fictional description is more real than what people realize. It has been fifty years since the launch of the first satellite, Russia’s Sputnik. Since then, as is the case with rapidly advancing technology, satellites have only proliferated and become more entrenched in society’s existence. This has created an incredible amount of crowding in the earth’s orbit that will only get worse as time progresses.
The current space debris is tracked by both the US Space Surveillance Network and US Strategic Command. They keep a data base of all objects in Low Earth Orbit (LEO) larger than 5 centimeters in diameter and all object in geosynchronous orbit (GEO) larger than one meter in diameter. There are currently 12 000 catalogued objects, of which only 850 are active satellites. Several thousand more cannot be catalogued because their origin is unknown. Several events in recent history have complicated the situation in the skies, however.
The main source of orbital debris for the last half century was in fact the ordinary breakup of satellites in orbit, the wear-and-tear of constant use. In the 1980’s, the US and Soviets tested anti-satellite (ASAT) weaponry, leaving much shattered satellite debris. One US test was conducted in September 1985 and the last piece of catalogued debris decayed from orbit only three years ago. However, both the Soviets and the Chinese have resumed their ASAT testing programs earlier this year. In January of 2007, the Chinese used a kinetic-energy ASAT weapon to destroy their dysfunctional Feng Yun-1C, increasing its percentage of the total orbital debris to 20%. The next month Russia exploded a Briz-M rocket booster stage, raising its total percentage to 40%. The implications of this newly created space jam are numerous.
While today, satellites are rarely damaged like the fictional account described earlier, orbital collisions are becoming more frequent. Through the nineties and into the current decade, collisions occurred about every five to eight years. Catastrophic collisions, involving total destruction of the objects that collided, were estimated to occur only every nineteen years. For different orbital radii, there are different risk levels. The most crowed highway around the globe is the 800 km elevation. Not only is the most debris concentrated at this altitude, but it is the most common orbital height for civilian satellites. Now, the countless remains of Feng Yun-1C and the Briz-M booster are circumnavigating Earth at that radius as well. The SSN predicts that because of the many small, un-chartable remains of those two satellites, the collision risk would nearly double. Collisions would occur every three to four years and catastrophes would fall in the five to ten year range.
However, a majority of these particles, as previously stated, are very small. Therefore, it would seem that the danger posed by these objects is very low and almost negligible. Basic kinetic energy theorems would disprove this notion. These objects orbit with speeds around 10 km/s. Consider most of these to be around one gram. Taking kinetic energy to be
the kinetic energy of one of these particles would equal 50 000 Joules. In comparison, a 100 kg mass traveling at 100 km/hr has only 38 580 Joules. Therefore, these collisions are extremely dangerous for orbiting satellites.
NASA has implemented ordinances to prevent the spread of orbital debris. Also, in 2002, the Inter-Agency Space Debris Coordination Committee set guidelines in place covering the production of such debris. The Orbital Debris Program Office issued a study in 2006 (before the Chinese and Russian ASAT tests) that some areas of space had already reached a super critical debris density. Therefore, these guidelines are of the utmost importance. However, there is no law passed to limit orbital breakup. The United Nations patterned guidelines after the IADC, and were seeming to be effective for some time. While there was a steady increase in orbital debris up through the mid nineties, it began to taper off into the new millennium. Unfortunately, the Russian and Chinese ASAT tests have caused a tremendous backslide in the effort to clear up the skies.
While it may seem minor and insignificant now, the problem of orbital debris will only deteriorate as time progresses unless action is taken soon to mitigate the situation. The more debris placed into space, the more regions will become super critical in status. The future of safe space travel depends on the control and containment of our orbital junk.
Wright, David. “Space Debris.” Physics Today. 60.10 (October 2007): 35-40
NASA Orbital Debris Program Office. 2007. 8 December 2007.