page_title: Upper Atmosphere Research Satellite
section_title: Active Cavity Radiometer Irradiance Monitor II (ACRIM2)
hierarchical_section_title: Upper Atmosphere Research Satellite / Instruments / Energy inputs / Active Cavity Radiometer Irradiance Monitor II (ACRIM2)
caption_attribution_description: English: ACRIM II instrument aboard the Upper Atmosphere Research Satellite
context_page_description: The Upper Atmosphere Research Satellite was a NASA-operated orbital observatory whose mission was to study the Earth's atmosphere, particularly the protective ozone layer. The 5,900-kilogram satellite was deployed from Space Shuttle Discovery during the STS-48 mission on 15 September 1991. It entered Earth orbit at an operational altitude of 600 kilometers, with an orbital inclination of 57 degrees.
  The original mission duration was to be only three years, but was extended several times. When the mission finally ended in June 2005 due to funding cuts, 14 years after the satellite's launch, six of its ten instruments were still operational. A final orbit-lowering burn was performed in early December 2005 to prepare the satellite for deorbit. On 26 October 2010, the International Space Station performed a debris-avoidance maneuver in response to a conjunction with UARS.
  The decommissioned satellite re-entered Earth's atmosphere on 24 September 2011. Considerable media attention surrounded the event, largely due to NASA's predictions that substantial parts of the satellite might reach the ground, potentially endangering inhabited areas.
context_section_description: The ACRIM2 instrument on the UARS satellite measured the total solar irradiance (TSI), the total solar radiant energy reaching Earth, continuing the climate change database begun in 1980 by the ACRIM1 experiment on the Solar Maximum Mission (SMM). The ACRIM1 experiment's results provided the first discoveries of intrinsic variations in the TSI and their relationships to solar magnetic activity phenomena. ACRIM experiments have confirmed TSI variation occurs on virtually every timescale from their 2-minute observation cadence to the decades-long length of the TSI record to date. A precise knowledge of the TSI and its variation over time is essential to understanding climate change. Recent findings indicate that instrinsic TSI variation has had a much larger role (up to 50%) in global warming during the industrial era than previously predicted by global circulation models (GCM's). The profound sociological and economic implications of understanding the relative climate change contributions of natural and anthropogenic forcings makes it essential that the TSI database, a critical component of climate change research, be carefully sustained into the foreseeable future. The UARS/ACRIM2 experiment was an important part of providing the long term TSI database.
caption: A photo of the UARS/ACRIM2 Total Solar Irradiance monitoring instrument.
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