Back in 1969, space travel was one giant leap for mankind. Now, it might be one giant mess. With rocket launches hitting record numbers in recent years and a calendar full of space missions in 2025, space is busier than ever. Among the satellites and space stations, there’s a telltale sign that space is getting some serious traffic: space junk is everywhere. So, what is space junk, exactly? And, considering we can’t just drag our bins out for collection 1000kms above Earth, how do we deal with it? With the help of one of Australia’s leading space debris experts, Deakin’s Shannon Ryan, we talk about this messy subject……..Continue reading…
By: Shannon Ryan
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At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag, lunar perturbations, Earth’s gravity perturbations, solar wind, and solar radiation pressure can gradually bring debris to lower altitudes (where it decays), but at very high altitudes this may take centuries. Although high-altitude orbits are less commonly used than LEO and the onset of the problem is slower, the numbers progress toward the critical threshold more quickly.
Many communications satellites are in geostationary orbits (GEO), clustering over specific targets and sharing the same orbital path. Although velocities are low between GEO objects, when a satellite becomes derelict (such as Telstar 401) it assumes a geosynchronous orbit; its orbital inclination increases about 0.8° and its speed increases about 160 km/h (99 mph) per year. Impact velocity peaks at about 1.5 km/s (0.93 mi/s).
Orbital perturbations cause longitude drift of the inoperable spacecraft and precession of the orbital plane. Close approaches (within 50 meters) are estimated at one per year. The collision debris pose less short-term risk than from a LEO collision, but the satellite would likely become inoperable. Large objects, such as solar-power satellites, are especially vulnerable to collisions.
Although the ITU now requires proof a satellite can be moved out of its orbital slot at the end of its lifespan, studies suggest this is insufficient. Since GEO orbit is too distant to accurately measure objects under 1 m (3 ft 3 in), the nature of the problem is not well known. Satellites could be moved to empty spots in GEO, requiring less maneuvering and making it easier to predict future motion.
Satellites or boosters in other orbits, especially stranded in geostationary transfer orbit, are an additional concern due to their typically high crossing velocity. Despite efforts to reduce risk, spacecraft collisions have occurred. The European Space Agency telecom satellite Olympus-1 was struck by a meteoroid on 11 August 1993 and eventually moved to a graveyard orbit. On 29 March 2006, the Russian Express-AM11 communications satellite was struck by an unknown object and rendered inoperable; its engineers had enough contact time with the satellite to send it into a graveyard orbit.
Space debris includes a glove lost by astronaut Ed White on the first American spacewalk (aka EVA), a camera lost by Michael Collins near Gemini 10, a thermal blanket lost during STS-88, garbage bags jettisoned by Soviet cosmonauts during Mir’s 15-year life, a wrench, and a toothbrush. Sunita Williams of STS-116 lost a camera during an EVA. During an STS-120 EVA to reinforce a torn solar panel, a pair of pliers was lost, and in an STS-126 EVA, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag.
An in-orbit fragmentation occurs when an artificial object in space unexpectedly breaks apart or sheds material outside its intended mission profile, serving as the primary generator of catalogued space debris. Historically, the majority of fragmentation events were caused by the sudden explosion of spent rocket upper stages and decommissioned satellites due to internal pressure build-ups or residual propellants.
However, deliberate weapon testing and accidental hypervelocity impacts are also significant drivers of the orbital debris population. A significant portion of debris is due to rocket upper stages (e.g. the Inertial Upper Stage) breaking up due to decomposition of unvented fuel. The first such instance involved the launch of the Transit-4a satellite in 1961. Two hours after insertion into orbit, the Ablestar upper stage exploded. Even boosters that do not break apart can be a problem. A major known impact event involved an intact Ariane booster.
Although NASA and the United States Air Force now require upper-stage passivation, other launchers– such as the Chinese and Russian space agencies– do not. Lower stages, like the Space Shuttle’s solid rocket boosters or the Apollo program’s Saturn IB launch vehicles, do not reach orbit.
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