The already untidy mass of orbital debris that litters low Earth orbit nearly got nastier last month. A head-on collision was averted between a spent upper stage from a Chinese rocket and the European Space Agency’s (ESA) huge Envisat Earth remote-sensing spacecraft.Space junk tracking information supplied by the U.S. military, as well as confirming German radar data, showed that the two space objects would speed by each other at a nail-biting distance of roughly 160 feet (50 meters).

ESA’s Envisat tips the scales at 8 tons, with China’s discarded rocket body weighing some 3.8 tons. A couple of tweaks of maneuvering propellant were used to nudge the large ESA spacecraft to a more comfortable miss distance. But what if the two objects had tangled?

Such a space collision would have caused mayhem in the heavens, adding clutter to an orbit altitude where there are big problems already, said Heiner Klinkrad, head of the European Space Agency’s Space Debris Office in Darmstadt, Germany.

It turns out, Klinkrad told SPACE.com, that 50 percent of all the close conjunctions that Envisat faces are due to the lethal leftovers from China’s January 2007 anti-satellite test, as well as chunks of junk resulting from last year’s smashup between an active U.S. Iridium satellite and a defunct Russian Cosmos spacecraft.

Klinkrad joined several orbital debris experts that took part in the 33rd Annual Guidance and Control Conference organized by the Rocky Mountain Section of the American Astronautical Society. The five-day meeting began Feb. 5.

Avoidance maneuvers

Significant progress has been made by the U.S. and the international aerospace communities in recognizing the hazards of orbital debris, reported Nicholas Johnson, chief scientist for orbital debris at the NASA Johnson Space Center in Houston, Texas.

Johnson added that steps are being taken to reduce or eliminate the potential for the creation of new debris. However, “the future environment is expected to worsen without additional corrective measures,” he noted.
During 2009, Johnson reported, five different NASA robotic spacecraft carried out collision avoidance maneuvers: a Tracking and Data Relay Satellite (TDRS-3), Cloudsat, Earth Observing Mission 1, Aqua, and Landsat 7. Also, the space shuttle and the International Space Station took collision avoidance actions, he said.

The worst thing that could happen, according to ESA’s Klinkrad, is the International Space Station (ISS) receiving a fatal hit. The space station is currently home to five astronauts representing the U.S., Russia and Japan. “A penetrating object hitting the ISS, and possibly causing a casualty onboard . . . I think that would be the most dramatic case we could have,” Klinkrad suggested. Such an incident might turn public opinion against human spaceflight, he said.

Collaboration on the increase

One bit of good news in all this orbital riff-raff. Due to last year’s satellite crash between the Iridium and Cosmos spacecraft, Johnson explained that the Joint Space Operations Center (JSpOC) of the U.S. Strategic Command now conducts conjunction assessments for all operational spacecraft in Earth orbit, regardless of ownership nationality. “To be honest, a year ago, we couldn’t even have hoped to have done this,” Johnson told SPACE.com.

“It’s really a consequence of the collision last year. People have been talking about this for years. But now we’ve made the commitment . . . that this is something that needs to be done and can be done relatively easily,” Johnson said. Klinkrad concurred. “The collaboration is getting even closer now,” he said.

Duck or pluck?

Playing dodge ball with high-speed space debris is one tactic. But there is also a growing interest in removing the most troublesome objects — perhaps an annual quota of some sort.Targeted would be specific inclination bands and altitude regimes, Klinkrad said. But prior to implementing debris remediation measures on a global scale, technical, operational, legal and economic problems must be overcome. Klinkrad and NASA’s Johnson provided a wearisome appraisal of the future.

Even with an immediate halt of launch activities, spacefaring nations will be dealing with an unstable low-Earth orbit environment in some altitude and inclination bands. This would be a consequence of about 20 catastrophic collisions within the next 200 years, the two orbital debris experts explained. Some orbit altitudes already have critical mass concentrations that will trigger “collisional cascading” within a few decades, unless debris environment remediation measures are introduced.

The Kessler Syndrome

The idea of debris creating debris was put in motion by Donald Kessler, along with fellow NASA researcher, Burton Cour-Palais, back in 1978. Their research suggested that, as the number of artificial satellites in Earth orbit increases, the probability of collisions between satellites also increases. Satellite collisions would produce orbiting fragments, each of which would increase the probability of further collisions, leading to the growth of a belt of debris around the Earth.Now, decades later, that prophecy has been dubbed the Kessler Syndrome.

Kessler told SPACE.com that the disorder fits into much more complex natural laws that include the evolution of the solar system, as well as meteoroids, meteorites, and climate-changing asteroids. Kessler is now an orbital debris and meteoroid consultant in Asheville, North Carolina.”There is nothing complex about what is called the ‘Kessler Syndrome’ . . . it is just the way nature may have converted a disorderly group of orbiting rocks into an orderly solar system . . . although nature reminds us with a large asteroid or comet collision every few million years that it isn’t quite finished yet. “In the case of orbital debris, this collision process is just starting,” Kessler explained. Consequently, nobody should be surprised that as orbital debris models became more complex — and as more data is obtained — the same conclusion holds, Kessler said.

“The future debris environment will be dominated by fragments resulting from random collisions between objects in orbit, and that environment will continue to increase, even if we do not launch any new objects into orbit,” Kessler concluded.

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• Video — The Expanding Danger of Space Junk

http://www.space.com/missionlaunches…er-100223.html

Tags: nasa, space junk, space.com