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.
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.
• 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