The United States is another contributor to the high levels of radiation in near-Earth space. In April 1964, its Transit-SB navigation satellite with a radio isotope generator aboard failed to enter orbit and broke into pieces. While burning up in the atmosphere, it scattered about a kilogram of plutonium-238 over the western part of the Indian Ocean north of Madagascar. The result has been a 15-fold increase in background radiation around the world.

A few years later, the Nimbus-B weather satellite with a uranium-235 reactor crashed into the Indian Ocean. Today, there are seven American radiation sources circling the Earth in orbits ranging from about 497 to 683 miles, and two more in near-geostationary ones.

The lurking threat of both Russian and American nuclear satellites is that, should they fall apart upon collision with space debris, vast expanses of near-Earth space would be contaminated.

Additionally, if some of the fragments had a velocity after collision and destruction that was below orbital speed, they would fall out of orbit and pollute some parts of the Earth's surface. In the worst-case scenario, the atmosphere could be heavily contaminated.

Now that we have ascertained the threat, it is necessary to think of ways to confront it and, if that is impossible, to deal with its effects.

For a start, it is important to cut the number of craft launched by increasing their useful life and using multipurpose satellites. Once they have served their purpose, they can be brought to the denser layers of the atmosphere using their remaining fuel, where they will burn up or enter less "populous" orbits. The second option is preferable. The satellite cemetery is expected to lie 124-186 miles above the area of geostationary orbits.

Directly cleaning up accumulated garbage from near-Earth space appears problematic for the foreseeable future. One idea is to use lasers. But complete evaporation of even a relatively small bit of substance would require considerable energy. Besides, some of the materials exposed to laser action will simply break up into smaller pieces, increasing the total number of fragments.

Lastly, this method is dangerous because it releases enormous energy into the environment. This energy might not only upset the environment's heat balance but also alter its chemical composition.

Unfortunately, no effective practical techniques exist today to protect against space pollution at altitudes where the cleaning-up effect of atmospheric drag on a satellite is absent.

On the other hand, the piling up of man-made debris in space poses the threat that once some critical level is achieved, an avalanche-like buildup may begin as pieces of rubbish start multiplying in mutual collisions.

After a time this may make working in space impossible.

(Yury Zaitsev is an expert with the Space Research Institute of the Russian Academy of Sciences. This article is reprinted by permission of the RIA Novosti news agency. The opinions expressed in this article are the author's and do not necessarily represent those of RIA Novosti.)

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