Space Debris
Collection of Objects in Orbit Around Earth



Space Debris
Collection of Objects in Orbit Around Earth

Human activities are not only leaving wastes on the Earth, but also polluting space. Space debris has posed a great concern in the countries which pursue space exploration.

SPACE IS NO LONGER A CLEAN PLACE

Since the former Soviet Union sent the first satellite into space in 1957, human exploration of space has left numerous debris, or rubbish, in the vast space.


Space debris refers to artificial objects or fragments cast off in space, whether on purpose or not. A total of 29,000 larger pieces of space debris have been tracked in the past 48 years of space activities. About 20,000 of them have fallen to the Earth.

Currently, 9,600 pieces of space debris which are larger than 10 cm are monitored. Only the United States and Russia conduct monitoring all such debris, said Gong Jiancun, a research fellow with the space technology and application center under the Chinese Academy of Sciences.

The pieces bigger than one mm but smaller than 10 cm cannot be monitored, Gong said, and those smaller than one mm pose no disastrous threat to space vehicles.

There are some 500 pieces of space debris passing through the orbit of Shenzhou-6 spacecraft, which is flying in a circular orbit 343 km above the Earth. It is able to resist the hit by debris less than one mm in size, said Gong.

About 45 percent of space debris was produced by the United States and 48 percent by Russia or former Soviet Union. China produced only 1.2 percent.

GROWING THREAT TO SPACE MISSIONS

The average speed of space debris is 10 km per second and the maximum speed can be 16 km per second.

Explosion or disassembly could happen if the craft is hit by a large piece of space debris.So far, three disastrous collisions have occurred, according to Gong.


Even a 10-gram piece of debris can generate a collision force in space equaling to the crash of a car running at 100 km per hour,said Du Heng, chief scientist with China's space debris action program.

On the average, a space shuttle has to reinstall 1.41 windows after each flight, according to the National Aeronautics and Space Administration of the United States. In July 1999, 64 collision traces were found on the American space shuttle "Discovery" after it returned to the Earth.

Most debris float in a zone 300 to 2,000 km from the Earth, where most space activities are carried out, and the number of debris larger than 10 cm is increasing by 200 each year.

Therefore, some scientists warn that if not controlled, the quantity of space debris will rise twice in 100 years, and no space vehicles can exist in space in a few centuries.

MONITORING, IMPROVING, AVOIDING

So far no effective way to collect space rubbish or avoid them from collision has been worked out. Satellite and spacecraft launchers can only try producing as less debris as possible while monitoring large debris and improving solidity of space vessels.


In 1993, the US, Japanese and European space authorities initiated the Inter-Agency Space Debris Coordination Committee. China joined the committee in 1995.

Today, less debris is produced by the explosion of abandoned rockets with surplus fuel. The committee is working on the design and production standards of space vehicles in the effort to reduce debris, according to Du Heng.

Improvement in spacecraft has also been made, including strengthening solidity and designing special protection areas. The measures on the International Space Station seem effective in resisting the collision with small debris, said Du.

Space powers are also trying to enhance monitoring abilities, wanting to lower the size of traceable debris to one cm.

China's task in the next five years is to independently monitor large debris, he said.

However, to avoid approaching large debris is the best way. The United States requires its space vessels to have an orbit maneuver when a piece of space debris is monitored 25 km ahead. China sets the safety distance at 100 km for Shenzhou-6, said Gong.

According to figures released by the US National Aeronautics and Space Administration, in the 50-odd flights from 1988 to 1997, its space shuttles changed orbit to avoid space debris at least five times.


Tracking Space Debris
Video courtesy of ESA (European Space Agency)
Tracking space debris for collision avoidance and human flight safety has been a priority for government space agencies since the launch of Sputnik 1 in 1957.

Yet the most recent satellite collision has revealed a dangerous void in tracking capabilities, proving that without a comprehensive system, the number of space objects in orbit will only continue to increase.

A comprehensive catalog of space objects being developed now for the U.S. Air Force, using Objectivity's object-oriented database management solution (Objectivity/DB), could be the key to predicting and preventing catastrophic collisions in the future.

Using the Objectivity/DB-powered system, the U.S. Air Force will be able to track space objects in real-time, so that decisions about spacecraft placement and collision avoidance can be made in seconds, rather than hours or days. Objectivity/DB will also allow the system to scale nearly infinitely as the catalog grows larger.

EOS Tracking Space Junk
Electro Optic Systems (EOS)
In less than 50 years of space travel you wouldn't believe the amount of galactic garbage we've created. There are millions of man-made pieces of junk including pieces of satellites, rocket bodies, even chips of paint!

All of them become potential lethal weapons against spacecraft because they are traveling at such high speeds. Something the size of a golf ball is enough to wipe out the entire space station!


Well, an Australian company has developed a state of the art tracking system to help avoid collisions with space junk. It's a laser system accurate enough to track junk only one centimeter in size.


The vast majority of space debris consists of small particles, from microns up to 1 centimetre (0.39 in).

Although there are an estimated 100 million such particles in orbit, they represent a tiny fraction of the total mass of human-made objects in space: perhaps 1%.


On impact, these particles cause damage similar to that from a micrometeorite and the widespread use of Whipple shields is effective against the damage they would otherwise cause.

Many parts of spacecraft, however, cannot be protected with Whipple shields and are subject to constant wear and tear. As these sorts of smaller debris represent the minority of the mass, and cause little damage, much of the focus on space debris risks centres on larger debris.

The exact definition of "larger" generally means "the size that can be tracked using current technology" and thus changes as tracking technologies improve.

In general, these objects are on the order of 10 centimetres (3.9 in) or larger and mass from about 1 kilogram (2.2 lb) and up. Collision with a fragment of this size at the average speed of 10 kilometres per second (6.2 mi/s) would be catastrophic.

As a result, space missions have to consider a number of operational factors and risk mitigation strategies.

 
Space debris is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose.

These objects consist of everything from spent rocket stages and defunct satellites to explosion and collision fragments.


Out of the estimated 600,000 objects above 1 centimeter (0.39 in) diameter, only 19,000 can be tracked as of today. This leads to wide uncertainties in the estimated quantities of debris, and the predicted path of their orbits.

If a collision with larger debris does occur, many of the resulting fragments from the damaged spacecraft will also be in the 1 kilogram (2.2 lb) mass range, and these objects become an additional collision risk.

As the chance of collision is a function of the number of objects in space, there is a critical density where the creation of new debris occurs faster than the various natural forces that remove these objects from orbit.

Beyond this point a runaway chain reaction can occur that quickly reduces all objects in orbit to debris in a period of years or months.

This possibility is known as the "Kessler Syndrome", and there is debate as to whether or not this critical density has already been reached in certain orbital bands.


The human race is known for causing vast amounts of pollution in the water that we drink, ground that we step on and air that we breathe, but it is also polluting the final frontier, space.

Most people are aware of the amount of garbage on Earth but many would be surprised just how much debris and junk is within space. There is so much junk that NASA has attempted to take some control over this issue.

Although most debris will burn up in the atmosphere, larger objects can reach the ground intact and present a risk.

The original re-entry plan for Skylab called for the station to remain in space for 8 to 10 years after its final mission in February 1974. Unexpectedly high solar activity pushed the space station's orbit closer to Earth than planned.

On July 11th, 1979, Skylab re-entered the Earth's atmosphere and disintegrated, raining debris harmlessly along a path extending over the southern Indian Ocean and sparsely populated areas of Western Australia.


On January 12th, 2001, a Star 48 Payload Assist Module (PAM-D) rocket upper stage re-entered the atmosphere after a "catastrophic orbital decay". The PAM-D stage crashed in the sparsely populated Saudi Arabian desert. It was positively identified as the upper-stage rocket booster for NAVSTAR 32, a GPS satellite launched in 1993.

The Columbia disaster in 2003 demonstrated this risk, as large portions of the spacecraft reached the ground. In some cases entire equipment systems were left intact. NASA continues to warn people to avoid contact with the debris due to the possible presence of hazardous chemicals.

On March 27th, 2007, wreckage from a Russian spy satellite was spotted by Lan Chile (LAN Airlines) in an Airbus A340, which was traveling between Santiago, Chile, and Auckland, New Zealand carrying 270 passengers.

The pilot estimated the debris was within 8 km of the aircraft, and he reported hearing the sonic boom as it passed.

The aircraft was flying over the Pacific Ocean, which is considered one of the safest places in the world for a satellite to come down because of its large areas of uninhabited water.


Woman hit by Space Junk
There has only been one recorded incident of a person being hit by human-made space debris.

In 1997 an Oklahoma woman named Lottie Williams was hit in the shoulder by a 10 x 13 centimetres (5.1 in) piece of blackened, woven metallic material that was later confirmed to be part of the fuel tank of a Delta II rocket which had launched a U.S. Air Force satellite in 1996.

She was not injured.