Disposal Practices Improve But Vary Among Countries
PARIS — Commercial satellite operators are getting better at removing their high-revenue-generating spacecraft from geostationary orbit early enough to keep them out of the way of current and future traffic there, but not everyone has adopted the rules, according to a European analysis of U.S. and Russian space-surveillance systems.
In 2007, 12 telecommunications satellites in geostationary orbit were retired. Eleven of them were guided into higher, unused orbits that will keep them at least 200 kilometers above the geostationary arc for 200 years – the guidelines adopted by the Inter-Agency Space Debris Coordination Committee (IADC).
All the major spacefaring nations are members of IADC, but judging from the results of the past two years, not all treat the guidelines with the same respect.
The 11 satellites that were correctly disposed of in 2007 were: NATO 4A, Meteosat 5, Satcom C4, DirecTV-2, GOES-9, Fengyun-2 1R, BSAT-1b, Thuraya 1, Hot Bird 1, JCSat 3 and N-Star 2, according to the Database and Information System Characterising Objects in Space (DISCOS) system maintained by the European Space Agency (ESA). The system uses data provided by ground sensors operated by the U.S. and Russian governments, and by European nations.
One satellite in 2007 – Russia’s Gorizont 26 – was placed into a graveyard orbit whose perigee is too low to prevent the satellite from eventually returning to perturb the geostationary arc.
Rudiger Jehn, a debris expert at ESA’sEsoc space operations center in Darmstadt, Germany, said Russian representatives to the IADC have said Gorizont 26 was launched in 1992, whereas the IADC guidelines were not adopted until 1997. “They have made clear they promise to do better for more-recent satellites,” Jehn said in a Jan. 31 interview.
Fernand Alby, a debris specialist at the French space agency, CNES, agreed that the trend appears to be toward more-thorough adoption of IADC-recommended practices, but that it is too early to confirm it.
In 2006, Alby said, 17 geostationary-orbiting satellites were retired, but only eight of them were correctly re-orbited – Intelsat 604, Astra 1B, Inmarsat 2F3, Galaxy 1R-A, N-Star 1, Raduga 1-6, Express-AM11 and Hot Bird 1.
Seven satellites were reorbited, but to destinations that are considered too low to meet the IADC guidelines. These satellites were Spacenet 4, Gorizont 25, Hispast 1B, Gorizont 31, Tempo 2, Thaicom 3 and FengYun 2.
Two satellites retired in 2006 simply were abandoned in the geostationary arc: Intelsat’s Galaxy 3R – which suffered a catastrophic failure – and the Russian Raduga 29.
Alby said that the regulatory policies of several nations – the United States, Britain and soon France, among others – offer clear incentives to satellite operators to clear their satellites from operating orbits as they retire.
But he said a Jan. 24 conference of satellite operators organized by CNES demonstrated the continuing difficulty of even well-intentioned operators in estimating how much fuel remains aboard their satellites.
“We got the clear sense that they are trying to do the right thing, but that it’s not so simple,” Alby said.
One revelation from the conference was the threat posed by spin-stabilized satellites as future debris agents. So-called “spinner” spacecraft stabilize themselves in orbit by spinning throughout their operational lives. But even when placed in correct graveyard orbits, they continue to spin. If in decades to come one of their components comes loose, or if these satellites are hit by a small object such as a meteorite, debris is more likely to ricochet into geostationary orbit even if the satellite otherwise has been emptied of its fuel.
Jehn said Eumetsat, Europe’s meteorological satellite organization – whose geostationary satellites up to now have all been spinners – has developed a procedure to slow down the spin of their satellites as they are maneuvered into the graveyard orbit.
“This is not as easy as it sounds and is just one illustration of issues that operators face,” Jehn said. Spin-stabilized satellites are only rarely used now, but in the 1980s and early 1990s the world’s most-popular commercial satellite design – the Boeing 376 – was a spinner.
Clearing the geostationary arc is a matter of self interest for every satellite operator insofar as most operators expect to use their existing, reserved orbital slots for new satellites when aging spacecraft are taken out of service. Operating two or more satellites at one orbital location is a common practice, but only when all of them can be carefully maneuvered to stay out of each other’s way.
Alby said that as of January 2008, 1,147 satellites or other objects presumed to be satellites were scattered along the geostationary arc some 36,000 kilometers above the equator. Of these, only 21 percent – 243 satellites – fully were controlled. Another 122 satellites were controlled on their east-west axis, meaning they can be kept from drifting along the arc and interfering with other satellites.
The remaining 782 satellites were abandoned in orbit.
In its January report on debris in all orbits, NASA counted 12,456 man-made objects in Earth orbit. Three quarters of them were spent rocket stages and pieces of satellites and launch vehicles.