Roamy here. With the impending splashdown of the Upper Atmosphere Research Satellite in the news, you might wonder what NASA was doing with the satellite in the first place. I found a NASA video explaining UARS, but it’s kinda dry. So I thought I’d give it a shot and hopefully not get too bogged down in the details.
The big atmosphere worry in the 1980’s was the hole in the ozone layer, which led to the banning of chlorofluorocarbons (CFCs). UARS was delayed by the Challenger accident and was launched in September 1991. At least one of the instruments on UARS was mapping the ozone layer, another was looking at chlorine monoxide in the atmosphere, and others observed methane, water vapor and nitrogen compounds. Many of the instruments onboard UARS looked at the limb, or the edge of Earth with the thin blue line of atmosphere, sometimes with the Sun occulting. That’s where the UARS was looking through the atmosphere at the Sun. (I tried to word that better, but my brain is still suboptimal.)
UARS was launched in time to see some of the atmospheric effects due to the Mt. Pinatubo eruption in June 1991. Also, the second generation of an instrument flown on the Solar Max Mission measured the irradiance of the Sun, especially the ultraviolet wavelengths (data I use in my work). UARS operated long enough to see the differences in all of the above from solar maximum to solar minimum.