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UARS Re-Entry Overview

UARS Satellite

NASA’s decommissioned Upper Atmosphere Research Satellite (UARS) fell back to Earth between 5:23 p.m. and 7:09 p.m. HST Friday, Sept. 23, 20 years and nine days after its launch on a 14-year mission that produced some of the first long-term records of chemicals in the atmosphere.

The precise re-entry time and location of debris impacts have not been determined. During the re-entry period, the satellite passed from the east coast of Africa over the Indian Ocean, then the Pacific Ocean, then across northern Canada, then across the northern Atlantic Ocean, to a point over West Africa. The vast majority of the orbital transit was over water, with some flight over northern Canada and West Africa.

Six years after the end of its productive scientific life, UARS broke into pieces during re-entry, and most of it up burned in the atmosphere. Data indicates the satellite likely broke apart and landed in the Pacific Ocean far off the U.S. coast. Twenty-six satellite components, weighing a total of about 1,200 pounds, could have survived the fiery re-entry and reach the surface of Earth. However, NASA is not aware of any reports of injury or property damage.

The Operations Center for JFCC-Space, the Joint Functional Component Command at Vandenberg Air Force Base, Calif., which works around the clock detecting, identifying and tracking all man-made objects in Earth orbit, tracked the movements of UARS through the satellite’s final orbits and provided confirmation of re-entry.

“We extend our appreciation to the Joint Space Operations Center for monitoring UARS not only this past week but also throughout its entire 20 years on orbit,” said Nick Johnson, NASA’s chief scientist for orbital debris, at NASA’s Johnson Space Center in Houston. “This was not an easy re-entry to predict because of the natural forces acting on the satellite as its orbit decayed. Space-faring nations around the world also were monitoring the satellite’s descent in the last two hours and all the predictions were well within the range estimated by JSpOC.”

UARS was launched Sept. 12, 1991, aboard space shuttle mission STS-48 and deployed on Sept. 15, 1991. It was the first multi-instrumented satellite to observe numerous chemical components of the atmosphere for better understanding of photochemistry. UARS data marked the beginning of many long-term records for key chemicals in the atmosphere. The satellite also provided key data on the amount of light that comes from the sun at ultraviolet and visible wavelengths. UARS ceased its scientific life in 2005.

Because of the satellite’s orbit, any surviving components of UARS should have landed within a zone between 57 degrees north latitude and 57 degrees south latitude. It is impossible to pinpoint just where in that zone the debris landed, but NASA estimates the debris footprint to be about 500 miles long.

More info at NASA’s UARS page: http://www.nasa.gov/mission_pages/uars/index.html

Frequently Asked Questions: Orbital Debris

What is orbital debris?

Orbital debris is any man-made object in orbit about Earth which no longer serves a useful purpose.

What are examples of orbital debris?

Derelict spacecraft and upper stages of launch vehicles, carriers for multiple payloads, debris intentionally released during spacecraft separation from its launch vehicle or during mission operations, debris created as a result of spacecraft or upper stage explosions or collisions, solid rocket motor effluents, and tiny flecks of paint released by thermal stress or small particle impacts.

How much orbital debris is currently in Earth orbit?

More than 22,000 objects larger than 4 inches (10 cm) are currently tracked by the U.S. Space Surveillance Network. Only about 1,000 of these represent operational spacecraft; the rest are orbital debris. The estimated population of particles between .4 inches and 4 inches (1 to 10 cm) in diameter is approximately 500,000. The number of particles smaller than .4 inches (1 cm) probably exceeds tens of millions.

Are orbital debris uniformly distributed about the Earth?

Most orbital debris reside within 1,250 miles (2,000 km) of Earth’s surface. Within this volume, the amount of debris varies significantly with altitude. The greatest concentrations of debris are found near 500-530 miles (800-850 km).

How fast are orbital debris traveling?

In low Earth orbit (below 1,250 miles, or 2,000 km), orbital debris circle the Earth at speeds of between 4 and 5 miles per second (7 to 8 km/s). However, the average impact speed of orbital debris with another space object will be approximately 6 miles per second (10 km/s). Consequently, collisions with even a small piece of debris will involve considerable energy.

How is the International Space Station protected against orbital debris?

The International Space Station, or ISS, is the most heavily shielded spacecraft ever flown. Critical components such as habitable compartments and external high pressure tanks normally will be able to withstand the impact of debris as large as .4 inches (1 cm) in diameter. ISS also can maneuver to avoid tracked objects. ISS executes a collision avoidance maneuver once a year on average.

How long will orbital debris remain in Earth orbit?

The higher the altitude, the longer the orbital debris will typically remain in Earth orbit. Debris left in orbits below 370 miles (600 km) normally fall back to Earth within several years. At altitudes of 500 miles (800 km), the time for orbital decay is often measured in decades. Above 620 miles (1,000 km), orbital debris normally will continue circling Earth for a century or more.

Is re-entering debris a risk to people and property on Earth?

A significant amount of debris does not survive the severe heating which occurs during re-entry. Components which do survive are most likely to fall into the oceans or other bodies of water or onto sparsely populated regions like the Canadian Tundra, the Australian Outback, or Siberia in the Russian Federation. During the past 50 years an average of one cataloged, or tracked, piece of debris fell back to Earth each day. No serious injury or significant property damage caused by re-entering debris has been confirmed.

What can be done about orbital debris?

The most important action today is to prevent the unnecessary creation of additional orbital debris. This can be done through prudent vehicle design and operations. Cleaning up the environment remains a technical and economic challenge that is currently being investigated by the United States and other countries.

What is the U.S. policy on orbital debris?

Since 1988 the official policy of the United States has been to minimize the creation of new orbital debris. The most recent National Space Policy (June 28, 2010) contains a section entitled “Preserve the Space Environment” that addresses orbital debris mitigation for both the near term and long term. In 2001 the United States adopted a set of measures for government agencies and departments called orbital debris mitigation standard practices. These standard practices became the foundation for the development of international orbital debris mitigation guidelines.

Do other countries have guidelines on orbital debris?

Yes, Russia, China, Japan, France, and the European Space Agency have all issued orbital debris mitigation guidelines. In addition, in 2007 the United Nations, through its Committee on the Peaceful Uses of Outer Space, created a set of orbital debris mitigation guidelines.

Where can I read more about orbital debris?

Visit the NASA orbital debris website at www.orbitaldebris.jsc.nasa.gov.