Crucial parts of a Canadian space instrument riding aboard a de-orbiting satellite may survive re-entry into the atmosphere and fall toward earth, according to its York University designers.
NASA reports that most of its 6.5-ton Upper Atmosphere Research Satellite (UARS) will burn up in the atmosphere, but says dozens of small pieces could strike earth when the satellite drops from orbit on Friday. The satellite, launched by the space shuttle in 1991, has been gradually losing 
altitude since 2005. On board is Canada’s Wind Imaging Interferometer (WINDII), an experiment led by York’s Gordon Shepherd (right). The 320-pound instrument was designed and built in Canada with the assistance of France.
“The heart of WINDII – the Michelson interferometer – is made of glass pieces cemented together. The glass would not evaporate and should reach the surface [of the earth],” says Shepherd, Professor Emeritus of Space Science in York’s Faculty of Science & Engineering. “The possibility that debris could land in Toronto is, of course, miniscule, but this is still very exciting,” he says.
Sponsored by the Canadian Space Agency and France’s Centre National d’Etudes Spatiales (CNES), the $40-million instrument is one of ten on board UARS. It was used to measure winds between altitudes of 80 and 300 km, discovering hurricane-force gales high above the earth. At the time, winds in the upper atmosphere were largely unknown territory (see YFile, Jan. 5, 2006).
WINDII used a technique, conceived by Shepherd and colleagues, called Doppler Michelson imaging, which allowed them to “see” the wind, even though the satellite orbited hundreds of kilometres above where such winds occur. It measured “airglow” – emitted by oxygen atoms and molecules in the atmosphere during the release of stored chemical energy – which tracked the 
movement of these atoms by measuring shifts in the wavelengths of light they emit.
Left: WINDII was used to measure winds in the upper atmosphere
NASA will issue updates on the satellite’s progress from its Joint Space Operations Center at Vandenberg Air Force Base in California, which works around the clock detecting, identifying and tracking all man-made objects orbiting earth, including space junk. It has emphasized that the satellite’s re-entry poses no real threat to the public.
“The joke is that on Friday you should make sure you travel north of 57 North or south of 57 South [latitude]” Shepherd says. “Viewed against the earth, UARS travels northeast up to a latitude of 57 degrees, near Churchill, Manitoba, and then heads south to 57 degrees, around the tip of South America, then heads north again. So, most of the world population lives in the danger zone.”
Your chances of being struck by space junk? “You’re probably a lot more likely to win the lottery,” he says.