SAGE III on ISS

SAGE III on ISS is the fourth generation of a series of NASA Earth-observing instruments, known as the Stratospheric Aerosol and Gas Experiment. The first SAGE III instrument was launched on the Russian Meteor (satellite) spacecraft. The recently revised SAGE III will be mounted to the International Space Station where it will use the unique vantage point of ISS to make long-term measurements of ozone, aerosols, water vapor, and other gases in Earth's atmosphere. SAGE III on ISS is the fourth generation of a series of NASA Earth-observing instruments, known as the Stratospheric Aerosol and Gas Experiment. The first SAGE III instrument was launched on the Russian Meteor (satellite) spacecraft. The recently revised SAGE III will be mounted to the International Space Station where it will use the unique vantage point of ISS to make long-term measurements of ozone, aerosols, water vapor, and other gases in Earth's atmosphere. The first SAGE instrument was launched February 18, 1979, to collect data on the various gases in the atmosphere, including ozone. The data collected on SAGE I and the following instrument SAGE II, which began taking measurements in October 1984, were critical to the discovery of the Earth's ozone hole and the creation of 1987 Montreal Protocol, which banned ozone-depleting substances, such as chlorofluorocarbon (CFC). SAGE III on ISS is a nearly exact replica of SAGE III Meteor-3M, sent into orbit in 2001 on a Russian satellite. SAGE III Meteor-3M went out of service in March 2006 when the satellite's power supply stopped working. The new instrument was built in anticipation of being attached to the space station in 2005. A change in ISS design, however, put those plans on hold. The instrument was stored in a Class 100 clean room in a sealed shipping container under a continuous gaseous nitrogen purge. The purge kept clean dry 'air' inside the instrument. Recently, the opportunity arose for SAGE III to be placed on ISS, and build on the long record of stratospheric gas data that its ancestors created. The week of February 14, 2011, scientists at NASA Langley Research Center pulled the instrument from storage to begin initial testing and calibrations in preparation prepping it for launch. The 76-kilogram (168 lb) SAGE III instrument is a grating spectrometer that measures ultraviolet and visible energy. It relies upon the flight-proven designs used in the Stratospheric Aerosol Measurement (SAM I) and first and second SAGE instruments. The SAGE III design incorporates Charge Coupled Device (CCD) array detectors and a 16 bit A/D converter. Combined, these devices allow for wavelength calibration, a self-consistent determination of the viewing geometry, lunar occultation measurements, and expanded wavelength coverage. The SAGE III sensor assembly consists of pointing and imaging subsystems and a UV/visible spectrometer. The pointing and imaging systems are employed to acquire light from either the Sun or Moon by vertically scanning across the object. The spectrometer uses an 800 element CCD linear array to provide continuous spectral coverage between 290 and 1030 nm. Additional aerosol information is provided by a discrete photodiode at 1550 nm. This configuration enables SAGE III to make multiple measurements of absorption features of target gaseous species and multi-wavelength measurements of broadband extinction by aerosols. The SAGE III mission is an important part of NASA's Earth Observation System and is designed to fulfill the primary scientific objective of obtaining high quality, global measurements of key components of atmospheric composition and their long-term variability. The primary focus of SAGE III on ISS will be to study aerosols, clouds, water vapor, pressure and temperature, nitrogen dioxide, nitrogen trioxide, and chlorine dioxide. Aerosols play an essential role in the radiative and chemical processes that govern the Earth's climate. Since stratospheric aerosol loading has varied by a factor of 30 since 1979, long-term monitoring of tropospheric and stratospheric aerosols is crucial. SAGE III aerosol measurements will provide important contributions in the area of aerosol research. Clouds play a major role in determining the planet's solar and longwave energy balance and, thus, are important in governing the Earth's climate. SAGE III will provide measurements of mid and high level clouds including thin or 'sub-visual' clouds that are not detectable by nadir-viewing passive remote sensors. These observations are important because while low clouds primarily reflect incoming solar radiation back into space (acting to cool the planet), mid and high level clouds enhance the 'greenhouse' effect by trapping infrared radiation (acting to warm the planet). Also, the presence of thin cloud near the tropopause may play a significant role in heterogeneous chemical processes that lead to ozone destruction in mid-latitudes.