Wednesday, May 25, 2005

Space Junk

*Space Junk**

**Orbiting junk, from old satellites to space gloves, has scientists
worried for spacecraft - and engineers working on ways to clean it up.*
*
*Thousands of nuts, bolts, gloves and other debris from space missions
form an orbiting garbage dump around Earth, presenting a hazard to
spacecraft. Some of the bits and pieces scream along at 17,500 mph.

The distribution of space junk around Earth.

*Profile of space junk*

*> 8,927 *man-made objects officially tracked* *(up from 8,841 in July 1999)

*> 4 million *pounds of stuff

*> 110,000 *total objects* *1 centimeter and larger

Space Junk Highlights

*. Oldest debris still in orbit*

The US Vanguard 1 satellite, which was launched on March 17, 1958, and
worked for six years.

*. Most dangerous garment*

US astronaut Edward White's glove, lost during a Gemini-4 spacewalk in
1965, orbited Earth for a month at 17,398 miles per hour.

*. Heftiest garbage disposal*

The Mir space station, where cosmonauts jettisoned more than 200
objects, most of them bags full of garbage, during the station's first
10 years of operation.

*. Most debris from the destruction of a single spacecraft*

The explosion in 1996 of a Pegasus rocket used in a 1994 launch. The
blast generated 300,000 fragments bigger than 4 millimeters (0.15
inches). Some 700 of these objects were big enough to earn entries in
catalogs of large space debris. The explosion doubled the Hubble Space
Telescope's risk of colliding with a large piece of space junk.

*. Most heavily shielded spacecraft in history*

The International Space Station.

Source: European Space Agency

Further study:
http://www.orbitaldebris.jsc.nasa.gov/

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An article from CSMonitor on this subject (worth reading):

Lots in space

*Orbiting junk, from old satellites to space gloves, has scientists
worried for spacecraft - and engineers working on ways to clean it up.*

*By Peter N. Spotts
<http://www.csmonitor.com/cgi-bin/encryptmail.pl?ID=D0E5F4E5F2A0CEAEA0D3F0EFF4F4F3A0ADA0E2F9ECE9EEE5>
*/| Staff writer of The Christian Science Monitor/

If you want to get rid of an old fridge or an obsolete TV, you could
call for curbside pickup. But an obsolete satellite? Or a spent rocket?

Increasingly, the space about Earth is getting cluttered with such junk.
And it's not just messy, it's dangerous. Full-size rocket bodies can
destroy. Even smaller pieces - such as a 1965 space glove that zipped
around for a month at 17,000 miles per hour - amount to more than a
smack in the face. They can puncture space suits and cripple satellites.

Fortunately, the aerospace community is giving the problem increasing
attention. Engineers are considering everything from techniques for
rendering derelict satellites and boosters less harmful, to an
international "space traffic control" system, to Earth-based lasers that
can zap the stuff.

But the problem is expected to get worse as governments and companies
prepare to triple the satellite population over the next two decades and
send more people into space.

"If we don't change our ways, this could become a serious problem," says
William Ailor, who heads the Center for Orbital Reentry Debris Studies
at the Aerospace Corporation in El Segundo, Calif.

As if to underscore the concern over space-junk hazards, over the past
year the United States government has adopted spacecraft and
mission-design rules to minimize the contribution its spacecraft make to
the space-debris problem. Now, the International Bureau of the US
Federal Communications Commission (FCC) is putting the finishing touches
on proposed debris-reduction rules that would govern commercial
satellites as well. The drafts could hit the commissioners' in-boxes as
early as December, notes Karl Kensinger, associate chief of the bureau's
satellite division.

Ever since Sputnik, humans have lobbed more than 20,000 metric tons of
hardware into orbit. In addition, Dr. Ailor notes that the number of
operating satellites is expected to grow from 700 today to as many as
3,000 in 2020.

This hardware can yield space junk in several ways: When satellites
separate from their boosters, they shed shrouds and other bits and
pieces. They can collide. Boosters can malfunction and explode. Or spent
booster segments with still-pressurized fuel tanks can explode when hit
by debris or after joints weaken from the constant freezing and thawing.
Solid-fuel motors can give off "slag" as part of their exhaust plumes.

Even satellites parked in "graveyard" orbits can shed material over
time. Defunct nuclear-powered spy satellites launched by the former
Soviet Union are slowly leaking their sodium-based coolant. The lumps
have been tracked to lower and lower altitudes.

All of this junk can travel at sizzling speeds and packs a wallop,
according to Richard Crowther, a space consultant with the British
research and development firm QinetiQ. He notes that for an object to
remain in orbit at altitudes below 620 miles (1,000 km), it must travel
at speeds of nearly 18,000 miles per hour. It's within this region of
space that critical satellites and craft, including the International
Space Station and the shuttle, operate. A small coin hurtling along at
22,000 miles an hour hits with the impact of a small bus traveling at 62
miles an hour on Earth.

So far, spacecraft operators have experienced only one confirmed hit
from space junk and several near misses. The hit came in July 1996, when
a small French military satellite was struck by debris from an Ariane
rocket that had been launched in 1986. The debris hit the satellite's
altitude-control arm at more than 33,500 m.p.h. and knocked the craft
into a different orbit. Space shuttles have been guided out of the way
of potentially threatening debris at least eight times. The
International Space Station has performed orbital duck-and-weave
maneuvers at least three times.

In low-earth orbit, gravity and atmospheric drag help sweep a good
portion of humanity's leavings - from abandoned space stations and
rocket stages to astronauts' gloves and lens caps - back into the
atmosphere to burn up or break up. Many more of these objects at higher
orbits could remain in space for thousands of years or more.

In all, more than 9,000 objects larger than about 4 inches have been
cataloged. Within 1,200 miles of Earth, some 2,200 tons of debris
orbits. If smaller but still-lethal objects were included, the catalog
could number more than 100,000. Ailor adds that the figure is likely to
grow as the number of satellites mushrooms.

Confronted with growing space debris, the FCC is proposing that
applicants for new commercial satellites show that the craft is robust
enough to prevent fragmenting in the face of any remaining fuel,
pressurization, or sudden discharge of the crafts batteries. Ideally,
leftover fuel would be vented, as would any pressurized system. And
batteries would be discharged. The proposed rules also set guidelines
for moving an over-the-hill spacecraft into a disposal orbit.

But additional shielding or fuel add weight and thus cost. European
Space Agency engineers, for example, calculate a $2 million price tag
for the additional fuel needed to steer a 1-ton satellite from
geosynchronous orbit toward reentry into Earth's atmosphere.

Others suggest more high-tech approaches, such as using ground-based
lasers to zap orbital debris - a plan that also could have space-weapon
implications. The idea, which NASA reportedly pronounced workable after
studying the approach in the late 1990s, relies on high-powered lasers
to vaporize small bits of material from the surface of a hunk of space
junk. The vapor emitted acts like a tiny rocket motor, propelling the
junk either into a less threatening orbit or on a path toward a fiery
reentry.

Others have proposed using space tethers, which a satellite could lower
at the close of its career. Taking advantage of electrical properties
induced at each end by its motion through Earth's magnetic field, the
tether would slow the satellite, dropping it into ever-lower orbits
toward reentry.

Even if these approaches prove practical, Ailor maintains that space
debris and growing traffic raise the need for an international
space-traffic control system. Currently, the US Air Force maintains the
9,000-entry catalog of large objects. But it warns the relevant agency
only if a manned vehicle is threatened.

Unfortunately, Ailor concludes, it may take a high-profile collision to
jump-start the kind of system he envisions.

:-)
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