From volcanic eruptions to ozone holes, a NASA instrument that monitors Earth’s upper atmosphere marks twenty years in orbit.

The Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument was deployed October 5, 1984, from the Space Shuttle Challenger aboard the Earth Radiation Budget Satellite (ERBS.) Originally scheduled for a two-year mission, SAGE II continues to give scientists a wealth of data on the chemistry and motions of the upper troposphere and stratosphere.

“The importance of the SAGE II data is helping to solve some exceedingly important societal issues like ozone depletion and greenhouse warming,” said SAGE II principal investigator Dr. M. Patrick McCormick, Co-Director of the Center for Atmospheric Sciences at Hampton University, Hampton, Va. “SAGE II has been a defining experience for my career and me.”

Managed by NASA Langley Research Center in Hampton, Va., SAGE II is part of NASA’s Earth Radiation Budget Experiment (ERBE.) The series of satellites launched in the mid -1980s were designed to investigate how energy from the Sun is absorbed and re-emitted by the Earth – one of the main processes that drive weather patterns. Observations from the ERB satellite are also used to study the effects on the Earth’s radiation balance from human activities — burning fossil fuels and the use of chemicals — and natural occurrences such as volcanic eruptions.

“While SAGE II is probably not the household name that say a Hubble is, it has had an impact on the average person, said Joe Zawodny, SAGE II Science Mission Manager at NASA Langley. “The international ozone assessments have brought the international community to action in a rare and unified way via the Montreal Protocol, and subsequent amendments. One result of this action is the virtual elimination of CFCs (chemicals harmful to ozone) and the subsequent adoption of the new technology in consumer devices such as auto and home air conditioning, refrigeration, and industrial uses.”

SAGE II has measured the decline in the amount of stratospheric ozone globally and over the Antarctic since the ozone hole was first described in 1985.

“The number one impact SAGE II data have had on the global scientific community is most certainly the 20 years of high quality ozone measurements and the ability to monitor the ozone profile for trends and changes throughout the stratosphere,” added Zawodny. “The understanding of the mechanisms behind the Antarctic Ozone Hole was derived partly from SAGE II ozone and polar stratospheric cloud data.”

Polar stratospheric clouds (PSCs) act as a medium to create ozone-destroying chemicals. And similar to ozone, SAGE II aerosol data have been important for determining the impact of volcanic aerosols on temperatures in the stratosphere and at the Earth’s surface. Three months after the 1991 Mt. Pinatubo eruption in the Philippines, scientists found that the stratospheric region at latitudes near Mt. Pinatubo had warmed 2.5-3o Centigrade (4.5- 5.4o Fahrenheit) due to the increased concentrations of aerosols.

SAGE II, built by (then) Ball Aerospace Systems Group, has added 18 years to the original mission life of twenty-four months on ERBS. However, the SAGE II experiment literally had a shaky start. After deployment from the Space Shuttle Challenger (STS-41G,) one of the ERBS’ solar arrays – the panels that provide power to the satellite – failed to deploy. Challenger mission specialist, Astronaut Sally Ride, had to shake the satellite with the remote manipulator arm and then finally place the stuck panel into sunlight for the panel to extend.

“The public should appreciate the investment they made into a satellite mission that has exceeded all predictions and hopes of a long life,” added McCormick. “And for its contributions to making Earth a better place now and for subsequent generations.”

SAGE II is part of the Earth science research heritage under the NASA’s Science Mission Directorate. Its Sun-Earth Mission is dedicated to understanding the Earth as an integrated system and applying Earth system science to improve the prediction of climate, weather, and natural hazards using the unique vantage point of space.