Overview Solar Stellar Irradiance Comparison Experiment Solstice

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The Solar Stellar Irradiance Comparison Experiment (SOLSTICE) is one of four measurement processes launched with the Solar Radiation and Climate Experiment (SORCE) mission for NASA, engineered and provided by the University of Colorado on January 25, 2003.  This specialized equipment follows up a previous SOLSTICE launched aboard the Upper Atmosphere Research Satellite (UARS) in 1991.

The new instruments measure the daily solar ultraviolet emissions (115-320nm) and compare these to the irradiance from a group of 18 stable bright blue early-type stars. The blue spectra emitted by these selected stars are measured as the satellite enters its nighttime section of orbit.  These stars are known to remain constant in time.  If there is any variation, then adjustments can be made to the data, knowing the instruments have changed their response. Instrument in-flight performance is thus monitored and a basis for comparison established for the future. The calibration for these instruments is unique in that it establishes these long-term corrections to sensitivity. 

There are actually two SOLSTICE instruments on board, known as SOLSTICE A and SOLSTICE B, for redundancy and for cross-calibration.  The very same stars are observed and results recorded as the earlier UARS satellite.  The mechanics are similar to the older optics and detectors, but with greatly improved accuracy and stability. Technical details and illustrations are available on the websites, linked below.

These inventions were designed, built, calibrated and tested by the University of Colorado’s Laboratory for Atmospheric and Space Physics (LASP). This department was overseen and supported by NASA’s Goddard Space Flight Center. LASP is responsible for all the data collection, processing, management and distribution of information, while NASA, of course, is responsible for the launches from Kennedy Space Center. As some of the SORCE functions were sub-contracted to Orbital Sciences Corporation in Dulles, VA, this entire project is a good example of how universities, NASA, and private industry can combine to advance the sciences and to help find solutions for Earth climate changes.

The focus for the SOLSTICE data is the stratospheric ozone layer and how it is affected by the solar radiation. The measurement of atmospheric ozone and UV-B radiation is critical to studies of the Sun and its effect on Earth, and the influence on human survival. LASP maintains several websites that explain and detail this project, SOLSTICE, as well as the overall mission of SORCE. The overall mission, of which SOLSTICE is a vital part, is to address long-term climate change, natural variability, and enhanced climate prediction.

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