NASA Satellite Falls Back to Earth This Weekend

A satellite the size of a school bus is expected to fall back to Earth sometime this weekend, NASA reports.

NASA's Upper Atmosphere Research Satellite, or UARS, is expected to re-enter Earth's atmosphere late this month or early next month, almost six years after the end of a productive scientific life, the space agency reported. Although the spacecraft will break into pieces during re-entry, not all of it will burn up in the atmosphere, the agency warned.

However, in a statement NASA claimed the risk to public safety or property is "extremely small" and reiterated that safety is NASA's top priority. As of Friday morning, the orbit of UARS was 100 miles by 105 miles. Re-entry is expected late today or early Saturday, Sept. 24. The agency said solar activity is no longer the major factor in the satellite's rate of descent and the satellite's orientation or configuration apparently has changed, and that is now slowing its descent.

"There is a low probability any debris that survives re-entry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent," NASA said in a statement posted on its Website. "It is still too early to predict the time and location of re-entry with any certainty, but predictions will become more refined in the next 12 to 18 hours."

NASA's UARS satellite, launched in 1991 from the space shuttle Discovery, was the first multi-instrumented satellite to observe numerous chemical constituents of the atmosphere with a goal of better understanding atmospheric photochemistry and transport. The school bus-sized satellite, which is 35 feet long and 15 feet in diameter, weighs 13,000 pounds, and carries 10 instruments, also provided key data on the amount of light that comes from the sun at ultraviolet and visible wavelengths. UARS ceased its productive scientific life in 2005.

In addition to numerous other scientific accomplishments, UARS data also marked the beginning of numerous long-term data records for many key chemical species in the atmosphere. This data is now being combined with more recent data sets (especially from NASA's Aura satellite) to better understand how the atmosphere reacts to the policies set down by the Montreal Protocol (an international treaty to protect the ozone layer by phasing out production of substances responsible for ozone depletion) as well as changes in climate drivers.

Since the beginning of the Space Age in the late-1950s, there have been no confirmed reports of an injury resulting from re-entering space objects, nor is there a record of significant property damage resulting from a satellite re-entry, according to NASA. That didn't stop late-night TV comedian Stephen Colbert, host of the satirical news program "The Colbert Report," from poking fun at NASA's advisory. "Let's just pray it lands somewhere where it can't do any damage-like Detroit," he quipped.