Pollution

Government Regulations

In the United States and many other nations, government regulations are the first line of defense against these problems. These regulations control manufacturing-related pollution in industries, including space-related ones, and are designed to prevent or reduce the escape of toxic chemicals into the environment and protect groundwater, the air, and the quality of life.

The regulations cover routine releases of propellant combustion products during testing, which in addition to their effects on human health can contribute to the formation of acid rain. Also, noise levels generated by the testing are strictly limited to prevent harm and disruption to people, animals, and property. The regulations also cover the disposal of rockets and missiles at the end of their useful lives. This too can involve harmful air emissions and hazardous chemical spills.

These environmental protections extend even to the early launch period. For example, the heat, vapors, and intensity of the space shuttle launch pose problems for the environment around the launch pad. In response, the National Aeronautics and Space Administration (NASA) ensures that the coastal wetlands and estuaries surrounding the launch center are not stressed beyond recovery. Trenches at the launch facility divert the boiling, mildly toxic ground cloud made of water from the main engines, which use the energy that results when hydrogen and oxygen combine to form water, and the more complex and damaging cloud from the boosters, which burn a solid propellant. The solid propellant cloud damages vegetation, increases water and soil acidity, and kills fish, but alternating launches between two pads and treating the soil and water reduces these problems and keeps them from expanding. Innovative reprocessing programs also lessen the impact. At the shuttle launch facility some of the launch emissions are rendered into a fertilizer used in local orange groves. But there are some environmental hazards rarely found outside the space industry that are associated with rocket exhaust and space debris.

Rocket Exhaust

Chlorine, nitrogen, and hydrogen compounds in both liquid and solid rocket propellants, such as the propellant used in the shuttle's boosters, were recognized in the early 1970s as agents of ozone destruction. Ozone protects us by absorbing the Sun's harmful ultraviolet rays and is concentrated between 15 and 30 kilometers altitude (9.4 and 18.8 miles), in the stratosphere.

Recent work indicates that significant ozone destruction resulting from rocket exhaust is brief and short-lived because launches are infrequent. Instead, the ozone loss is dominated by other sources of atmospheric pollution, such as the chlorofluorocarbon compounds used as a refrigerant and to make plastic foam. But other aspects of rocket exhaust affect the climate. Combustion products in the exhaust such as carbon dioxide, nitrous oxide, and water vapor are greenhouse gases and may contribute to global warming.

Particulates in the exhaust can interfere with the passage of sunlight and promote cloud formation, leading to unforeseen effects on the climate. These particulates can provide sites for ozone-depleting chemical reactions and thus boost the destructive power of the reactions.

Some propellants are highly toxic. Spills of the propellant heptyl left over in Soviet booster stages that have fallen to the ground in Russia's Altai Republic for decades may have caused unexplained medical and environmental problems there. Solving problems related to propellant characteristics will be done on both regulatory and technological fronts. The best solution may be the creation of new, less harmful propellants and the transfer of bases of operation into space.

Space Debris

Space debris is space travel's other major pollution problem. Also called space junk, it fills the near-Earth orbit and poses a threat to current and future efforts above Earth. Missions to other worlds also have the potential for contamination.

Space debris is the accumulation of rubbish since 1957 from rockets and satellites, some exploded and some obsolete. It includes discarded hardware no longer needed by piloted missions and gumball-size spheres of coolant that escaped from satellite reactors and froze in space.

Because of high speeds relative to a passing satellite, spacecraft, or space station, collisions with even small bits of this debris can do serious damage. Shields offer protection from the smallest pieces, and ground-based tracking systems provide advanced warning of the biggest hunks, allowing time for evasive action. But the most troublesome pieces fall between these sizes, ranging from a 1 centimeter (a half inch) to 10 centimeters (4 inches). These pieces are hard to track and plentiful, numbering more than 150,000.

A ground-based laser that destabilizes the orbit of this intermediate-size junk is one promising solution to this problem. Studied since the late 1970s, this approach would vaporize a thin layer of a piece of space junk as it approached, effectively creating a retrorocket that would slow it down. The laws of physics, which dictate a lower altitude when a body's orbital speed drops, then drop the piece into the atmosphere, which slows it more, eventually causing it to burn up in the atmosphere. Studies of the concept, planned for a test by 2003, estimate that Earth orbit could be cleansed of junk this size within two years.

Current Protocols

Protocols exist for avoiding pollution of other worlds. Payloads are scrupulously sterilized. Rocket stages that loft probes toward these targets are diverted to avoid trajectories that would follow the probe.

SEE ALSO SPACE DEBRIS (VOLUME 2).

Richard G. Adair

Bibliography

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