Debris-control Report Card Cites Improvement by Geo Sat Owners
PARIS — Five satellites in geostationary orbit owned by the governments of the United States, China, India and Indonesia were retired in 2012 into too-low orbits that did not meet internationally accepted debris mitigation guidelines, according to an annual assessment by European experts using U.S., Russian and European data.
For four of the five — the U.S. GOES-7, India’s Insat-2E, China’s Beidou 3 and Indonesia’s Palapa C1 — the owners made an attempt to raise the spacecraft into acceptable graveyard orbits, generally viewed as 250 kilometers above the geostationary belt 36,000 kilometers over the equator, but fell short.
The fifth, Indonesia’s Cakrawarta 1, appears to have been abandoned on the geostationary highway, according to the study, which was presented to the Inter-Agency Space Debris Coordination Committee (IADC). Among the governments cited for failing to properly dispose of geostationary-orbiting satellites in 2012, only Indonesia is not a member of the IADC.
Two other objects, a Russian Proton-K DM-2 upper stage and the apogee-boost engine on China’s Fengyun 2F satellite, were placed in disposal orbits that are far below IADC guidelines.
The geostationary orbit’s popularity as a destination for telecommunications and meteorological satellites is why orbital debris experts are concerned about its being polluted by dead spacecraft.
In-orbit collisions between geostationary satellites are not considered a serious threat for now, unlike the situation in low Earth orbit, where satellite and rocket-body concentrations are far greater. But the accumulation of satellites in the geostationary arc at some point will be problematic.
Currently ground radars count 1,369 objects in geostationary orbit. Nearly half of them are in an uncontrolled drift orbit. Another 178 dead satellites have converged at one of two libration points — around 75 degrees east and 105 degrees west longitude — on opposite sides of Earth, where uncontrolled satellites tend to collect because of irregularities in Earth’s gravity field.
As of January, only 21 percent of the identified objects in the geostationary-orbit arc were fully controlled on their north-south and east-west axes. Nine percent were controlled only on their east-west axes, a fuel-saving procedure often employed to extend a satellite’s life.
The annual study, compiled by the European Space Agency’s Space Debris Office at the agency’s European Space Operations Centre in Darmstadt, Germany, relies on data from a variety of sources. These include the U.S. Air Force’s Space Surveillance Network; the International Scientific Observation Facilities Network (ISON), which uses 50 telescopes in 13 nations and is coordinated by Russia’s Keldysh Institute of Applied Mathematics; and European telescopes.
While nine successful debris mitigation procedures out of a possible 14 in 2012 suggests room for improvement, the study’s authors say the situation has improved in recent years.
Under growing pressure from the IADC guidelines, and with debris mitigation having been adopted by the International Organization for Standardization (ISO) in 2010, more geostationary satellite owners are complying with the guidelines.
Two-thirds or more of the geostationary-orbit disposals up until the early 2000s were in violation of the guidelines, which were first presented to the United Nations in 2002. ISO-24113, which sets satellite repositioning requirements similar to the IADC’s, took effect in 2010.
The trend in recent years has been that two-thirds of the satellites retiring in geostationary orbit have been correctly repositioned.
The situation in low Earth orbit, where IADC guidelines ask that satellites and rocket bodies be positioned so that they re-enter the atmosphere and disintegrate within 25 years, is not as good.
The guidelines also stipulate that if, by its size or shape or orbit, an object poses a greater than one-in-10,000 risk of surviving atmospheric re-entry, it should be disposed of with a controlled descent into the atmosphere. This requires a substantial amount of fuel to guide the satellite so that it falls into a zone cleared of people — generally the south Pacific Ocean.
The study looks at rocket upper stages left in orbit whose perigees are less than 6,000 kilometers in altitude, and at satellites launched after 1990 and retired with perigees of less than 2,000 kilometers. Perigee refers to an object’s closest distance to Earth during each orbit.
For rocket upper stages initially left in an orbit of between 600 and 1,400 kilometers, adherence to the IADC guidelines remains poor. Of the 29 rocket bodies left in that zone in 2010 and 2011, only nine were positioned so as to assure a re-entry in less than 25 years.
The situation for low-orbiting satellites is even worse. Of the 38 satellites retiring at altitudes of 600-1,400 kilometers, just two are in orbits to assure re-entry in less than 25 years. Another two are expected to fall into the atmosphere in around 25 years, and the remaining 34 will remain orbital threats for longer than 25 years — in some cases, much longer.
The IADC and many of its member space agencies, including NASA, typically plot debris-buildup scenarios in different orbits assuming that, in the future, 90 percent of all satellites and rocket upper stages will be disposed of correctly at the end of their missions. That is far from being the case today.
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