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Stratospheric Aerosol and Gas Experiment III - International Space Station

Phase: Development

Launch Date: March 2016

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The SAGE III instrument is used to study ozone, a gas found in the upper atmosphere that acts as Earth’s sunscreen. More than 25 years ago, scientists realized there was a problem with Earth’s thin, protective coat of was thinning. The SAGE family of instruments was pivotal in making accurate measurements of the amount of ozone loss in Earth's atmosphere. SAGE instruments have also played a key role in measuring the onset of ozone recovery resulting from the internationally mandated policy changes that regulated chlorine-containing chemicals, the Montreal Protocol, which was passed in 1987.

Today, the SAGE technique is still the best for the job, and NASA scientists are preparing to send a SAGE III instrument to the International Space Station (ISS). Instead of flying on an un-manned satellite, SAGE III will be mounted to the ISS where it will operate alongside experiments from all over the world in the space-based laboratory. The orbital path of ISS will help maximize the scientific value of SAGE III observations.

SAGE III - ISS is scheduled to board one of NASA's first commercial Space X flights in 2014 for a ride to its new home. Once on ISS, SAGE III will do what it does best – Earth observations to extend a long record of atmospheric measurements for the continued health of Earth and its inhabitants.

More specifically, SAGE III - ISS will provide global, long-term measurements of key components of the Earth's atmosphere. The most important of these are the vertical distribution of aerosols and ozone from the upper troposphere through the stratosphere. In addition, SAGE III also provides unique measurements of temperature in the stratosphere and mesosphere and profiles of trace gases such as water vapor and nitrogen dioxide that play significant roles in atmospheric radiative and chemical processes.

To take these measurements, SAGE III relies upon the flight-proven designs used in the Stratospheric Aerosol Measurement (SAM I) and SAGE I and II instruments. SAGE III, like its predecessors, is a grating spectrometer that measures ultraviolet/visible energy. However, SAGE III has a few upgrades. The new 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, which is illustrated below, 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 them. 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.

These measurements are vital inputs to the global scientific community for improved understanding of climate, climate change and human-induced ozone trends.

Three copies of SAGE III were produced. One instrument was mounted on the Meteor-3M spacecraft that launched in 2001 and a second was carefully packed away awaiting a flight of opportunity. The SAGE III - ISS and the other two SAGE III instruments were developed and managed by NASA's Langley Research Center and built by Ball Aerospace in Boulder, Colo.