Humans throw incredible amount of trash on Earth. Because we have so many environmental issues on Earth, we may not think much about space junk. The landing of "Curiosity" last week on the Mars aroused my curiosity to research about Space debris. Hold your breath, NASA claims there are millions of objects, both small and large, orbiting Earth in a giant cloud of junk.

A few hours after the Curiosity successfully landed on Mars and began transmitting images of the Red Planet, a Russian rocket launched from Kazakhstan failed to deliver the satellites into orbit adding $2 million worth of space junk into Earth's orbit.

Space junk started during the 20^th century. The Soviet Union launched Sputnik I, the first satellite in history during 1957 and flagged off a space race. The event led Congress to create the National Aeronautics and Space Administration, or NASA. Subsequently Governments, cell phone, television and GPS receiver companies, have launched hundreds of satellites.

Space Debris includes

Abandoned spacecraft, that does not work anymore and is left to float around space. It is too expensive to retrieve these objects, so they are left there to circle the Earth until they fall back down or collide with other space junk.

Upper stages of launch vehicles - Space shuttles are launched using more than one rocket boost to get them high enough into space, and these rockets are fired off in stages. The final stages are called upper stages; they fire so late and get trapped in the Earth's orbit. They are some of the largest space junk.

Solid rocket motor effluents - Solid rocket fuel used for propulsion, can be left over and will float around in whatever container it flew up. This poses a great risk for collisions and creates more space junk after an explosion.

Tiny flecks of paint - There are millions of tiny pieces of paint floating around Earth's orbit. Heat or impacts with other small particles usually chip off paint specks from spacecraft and turn them into space junk.

It may be funny to note that there are even a few dead animals that were sent in the early years of space research and never came back to Earth.

For fifty years, the main source of all of the junk came from objects that exploded by accident. However, in 2007, the intentional destruction of the Chinese weather satellite Fengyun-1C as part of an anti-satellite missile test created significant amounts of space debris. Two years later, a defunct Russian military satellite struck an operational American Iridium satellite over northern Siberia, blowing even more trash into space. "We've lost control of the environment," said retired NASA senior scientist Donald Kessler during 2011 after heading the National Academy of Sciences report. "Those two single events doubled the amount of fragments in Earth orbit and completely wiped out what we had done in the last 25 years," Kessler said.

Some of this junk floats in space, while most of it orbits Earth at speeds of up to 36,000 km per hour. There are approximately 20,000 objects in orbit that are big enough for officials on the ground to track, and countless smaller ones.

Earth's gravitational field pulls a lot of space trash into lower and lower orbits until it finally reaches Earth's atmosphere. Most of the trash burns up when it enters Earth?s atmosphere. The higher the altitude at which it orbits the longer the space trash will remain in orbit. Space trash moving in orbits lower than 600 km normally falls back to Earth within a few years. Space trash orbiting at altitudes higher than 1,000 km can continue circling Earth for a century or more.

The Dangers of Space Junk

The main problem with space trash is the danger it poses to working satellites and manned spacecraft like the International Space Station (ISS). The ISS performs frequent collision avoidance maneuvers to reduce the risk of this happening. The danger was highlighted when astronauts on ISS were forced to take shelter inside two Soyuz capsules when debris came within 1,000 feet.

NASA frequently replaces Space Shuttle windows damaged by orbiting flakes of paint! Because of the very great speeds at which space trash travels, small pieces between 1 and 10 centimeters in size can penetrate and damage most spacecraft. A ten-centimeter long piece of space trash can cause as much damage as twenty-five sticks of dynamite!

For these reasons, NASA (together with the Department of Defense) has created a space surveillance network. Ground stations track larger pieces of space trash so that collisions with working satellites or the Space Shuttle can be avoided.

In the 2007 the General Assembly of the United Nations adopted measures to limit the production of more space debris. These include limiting the potential for break-up by venting fuel at the satellite's end of life and limiting the long-term presence of spacecraft at the end of their mission, either by de-orbiting or by moving to a "Graveyard orbit".Future plans include a cooperative effort among the governments of many nations to stop littering space and to possibly clean up the trash already there.

Ozone depletion

Fortunately, most debris burns up during reentry. The impact of the chemical reactions during reentry of space leftovers made of tungsten, beryllium, aluminum and lots of composite materials on Earth's atmosphere is still being researched.

One study team that studied the impact of de-orbiting space debris on stratospheric ozone for the Environmental Management Division of the Space and Missile Systems Center reported that objects re-entering the atmosphere can affect ozone in several ways, but not on a significant level globally. During re-entry, a shock wave is created that produces nitric oxide, a known cause of ozone depletion. Spacecraft and rocket motors are composed of materials that melt during re-entry. The researchers found that these materials undergo intense heating and form chemicals that react directly or indirectly to consume ozone.

Ross, along with Darin Toohey of the University of Colorado, Boulder's Atmospheric and Oceanic Sciences Department has reported that rocket launches may need regulation to prevent ozone depletion.

Some progress has been made on an International Code of Conduct for Outer Space Activities, which builds on the 1967 Outer Space Treaty. It will help maintain the long-term sustainability, safety, stability, and security of space by establishing guidelines for the responsible use of space.

Space Tourism

Environmentalists are disturbed to note that Virgin Galactic is soon going to launch commercial Space tourism. There is lot of concern that these flights would emit large amounts of black carbon soot and become a reason to alter global atmospheric circulation and distributions of ozone in the stratosphere. Currently, commercial rockets burn a mixture of kerosene and liquid oxygen that release large amounts of carbon. But several companies are attempting to change this by developing a more economical hybrid rocket engine that ignites synthetic hydrocarbon with nitrous oxide. Studies show that these new hybrid engines emit even more black carbon than a kerosene and oxygen engine.

Speaking about the potential impact last year, Martin Ross, an atmospheric scientist at the Aerospace Corporation in Los Angeles, California, said that over 1,000 space flights a year could increase polar surface temperatures by 1 degree centigrade and reduce polar sea ice by 5-15 percent. "There are fundamental limits to how much material human beings can put into orbit without having a significant impact", he said.

It is altogether another question whether the world needs this kind of luxury at all.

IS THE HUMAN RACE OF 7 BILLIONS DESTINED TO PAY HEAVILY IN THE NEXT MILLENNIUM?

To end this with a joke, at least let us hope the Spaceships do not end up leaving plastic covers and food in stratosphere, left there by the tourists !!