Duck! Look out for space junk (photos)
After two decades in orbit, a 6.5-ton U.S. science satellite will plummet to the earth
on Friday evening, Sep. 23 or early Saturday, Sept. 24. NASA officials estimate 1,200 pounds of debris will survive the atmospheric re-entry, but are unsure where the plunging debris will
precisely hit. The latest projections show that North America is not in the line of fire.
Before relegated to space junk, the Upper Atmosphere Research Satellite (UARS)
collected data about the earth's atmosphere soon after astronauts aboard shuttle
Discovery deployed it in September 1991. The $750 million was decommissioned in
late 2005 and allowed to enter a phase known as orbital decay.
Falling orbital debris poses little threat to people and property on earth. In fact,
not many will witness the firework display that UARS will create as it falls back to
earth and the chances of anyone in the world getting hit by a piece of it is 1 in 3,200.
According to NASA, over the past 40 years an average of one cataloged piece of
debris fell back to Earth each day.
The real danger, however, is in space. Researchers have warned that space junk
floating around the Earth poses more of a threat than ever to spacecraft in orbit.
On the following pages are ten factoids about space junk that every stargazer, amateur astronomer,
or armchair satellite tracker should know:
It’s not just whole, abandoned satellites that constitute space junk. The term also
encompasses pieces of broken satellites, deployed rocket bodies, human waste,
tiny flecks of paint released by thermal stress or small particle impacts and other
random human-made objects. For instance, the glove lost by astronaut Ed White
during his historic 1965 spacewalk.
A swarm of at least half a million and possibly even tens of millions of pieces of space junk is currently circling the earth. NASA approximates 19,000 objects in Earth orbit larger than 10 centimeters, about half-million particles between 1 and 10 cm in diameter, and tens of millions of particles smaller than 1 cm. The most concentrated area for orbital debris is in low Earth orbit (LEO), the region of space within 2,000 km of the Earth's surface. The geosynchronous region (around 35,785 km altitude) also contains space junk, mainly weather and television satellites.
Collisions between space junk and spacecraft happen all the time. Operational spacecraft are struck by very small debris and micrometeoroids routinely with little or no effect. Debris shields can also protect spacecraft components from particles as large as 1 cm in diameter. The Long Duration Exposure Facility (LDEF) was a bus-sized spacecraft that was returned after nearly 6 years in low Earth orbit. It had over 20,000 impacts.
The oldest known piece of orbital debris is over half a century old. The 1958 Vanguard 1 research satellite, which ceased all functions in 1964. It was the fourth satellite launched and the first to be solar powered. On March 17, 2008 it logged its 50th year in Earth orbit.
A U.S. and Russian satellite played chicken, both lost. The worst collision between space objects occurred on February 10, 2009 when an operational U.S. Iridium satellite and defunct Russian satellite above northern Siberia, creating an estimating 1,700 pieces of debris in the process.
The Hubble Space Telescope routinely captures detailed images of space and planet phenomenon, including asteroid collisions. The Hubble had its own close encounter in 2009 when an impact with space debris completely penetrated the antenna dish leaving of hole in the size of a .22-caliber bullet.
On July 11, 1979, Skylab, NASA's 85-ton space station returned to Earth burning up over the Indian Ocean and Western Australia. A few large pieces survived re-entry, making landfall southeast of Perth and elsewhere. Nobody was hurt, but the Australian town of Esperance slapped NASA with a $400 fine for littering. It was eventually paid by a California radio DJ in 2009 after collecting donations from his listeners.
Orbital debris radars like Haystack and HAX located in Tyngsborough, MA., collect orbital debris data by sampling the debris population by "staring" at selected pointing angles and detecting debris that fly through its field-of-view. The data are used to characterize the debris population by size, altitude, and inclination.
In June 2011, six astronauts evacuated the Space Station to avoid space junk hurtling towards them. It ended up passing within 820 feet of the ISS while the astronauts took refuge in a Russian spacecraft.
Japan is working on a plan to sweep up damaged satellites and space shuttles. They'll attach a thin metal net, which is several miles wide, to a satellite and then launch the pair into space where it will start picking up space junk in its path during a journey that is expected to last several weeks.