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| Solar Mesosphere Explorer | |
|---|---|
| Name | Solar Mesosphere Explorer |
| Names list | SME |
| Operator | National Aeronautics and Space Administration (NASA) |
| Manufacturer | Goddard Space Flight Center |
| Launch date | 1981-10-07 |
| Launch vehicle | Delta 3914 |
| Launch site | Vandenberg Air Force Base |
| Mission duration | 11 years (operational until 1990) |
| Orbit type | Low Earth orbit |
| Programme | Explorer program |
Solar Mesosphere Explorer was a NASA satellite mission designed to study the chemistry and dynamics of the upper atmosphere, with particular emphasis on the mesosphere and stratospheric ozone. Operated by Goddard Space Flight Center as part of the Explorer program, the spacecraft carried ultraviolet and visible spectrometers to measure ozone, water vapor, and related species affected by solar ultraviolet radiation and energetic particles. The mission provided multi-year, global coverage that informed atmospheric chemistry models used by research centers and international panels.
The mission was conceived at Goddard Space Flight Center in response to emerging concerns about stratospheric ozone and coupled solar-terrestrial influences highlighted by investigations at Jet Propulsion Laboratory, National Center for Atmospheric Research, and research groups at Harvard University and Massachusetts Institute of Technology. Managed by NASA Headquarters and funded under programs involving Office of Space Science and Applications collaborations, SME aimed to resolve discrepancies between ground-based ozone trends reported by observatories such as Mauna Loa Observatory and balloon-borne measurements from NOAA campaigns. The project interfaced with international efforts including the World Meteorological Organization and panels such as the International Ozone Commission to provide observational constraints for global assessments.
The spacecraft bus was developed at Goddard Space Flight Center incorporating heritage from earlier Explorer program platforms and engineering techniques refined during missions like Nimbus 7 and Orbiting Geophysical Observatory. Power was supplied by solar arrays and batteries used on contemporaneous spacecraft such as IUE and Solar Maximum Mission. Attitude control systems employed sensors and gyros similar to those on Landsat and communications subsystems used TDRSS-era design principles for data relay through ground stations at Wallops Flight Facility and the European Space Operations Centre.
Instrument payloads included a suite of ultraviolet and visible spectrometers developed in collaboration with laboratories at University of Colorado Boulder, University of Toronto, and industry partners including Ball Aerospace. Principal sensors were a radiometer and multiple spectrometers optimized for limb and solar occultation viewing to measure ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), water vapor (H2O), and aerosols. Detector technologies drew on photon-counting techniques advanced at Stanford University and cryogenic detector research from Caltech groups. Calibration standards referenced protocols from National Institute of Standards and Technology.
Launched on a Delta 3914 vehicle from Vandenberg Air Force Base on 7 October 1981, SME was inserted into a sun-synchronous low Earth orbit enabling frequent terminator and occultation geometries used for limb sounding. Mission operations were conducted from Goddard Space Flight Center mission control with support from the Air Force Satellite Control Network and international ground stations including Kiruna Geophysical Observatory and Svalbard Satellite Station to maximize polar coverage. Routine commanding, thermal management, and instrument sequencing followed operational practices developed during Nimbus missions and the Earth Radiation Budget Satellite era.
The spacecraft remained operational through 1990, surviving space environment challenges such as enhanced solar activity during the early 1980s and micrometeoroid environment assessments performed by teams at University of Colorado and NASA Ames Research Center. An end-of-mission decommissioning plan coordinated with United States Space Command procedures to mitigate orbital debris, leading to final passivation and telemetry termination.
Primary objectives were to quantify vertical profiles and temporal variability of ozone and related minor constituents in the mesosphere and upper stratosphere, to investigate photochemical processes driven by solar ultraviolet flux variations, and to assess the role of energetic particle precipitation in catalytic ozone loss cycles. SME measurements provided critical validation for photochemical models developed at Harvard-Smithsonian Center for Astrophysics, Max Planck Institute for Chemistry, and research consortia at NOAA and European Space Agency laboratories.
Key findings included characterization of mesospheric ozone depletion linked to solar UV changes and observations of nitric oxide increases associated with geomagnetic storms analyzed in conjunction with data from Ionospheric Research Group and magnetospheric missions like Dynamics Explorer. SME detected seasonal and latitudinal patterns in water vapor and aerosol distributions that improved representation in climate and chemistry models used by Intergovernmental Panel on Climate Change assessment teams. The dataset helped resolve discrepancies between satellite and balloon ozone retrievals reported by World Ozone and Ultraviolet Data Centre partners.
Raw telemetry and calibrated science products were processed by pipelines at Goddard Space Flight Center using algorithms developed with contributions from University of Michigan and University College London researchers. Level 1 radiance calibration referenced solar irradiance standards maintained by National Institute of Standards and Technology, while Level 2 retrievals employed inversion techniques refined at Jet Propulsion Laboratory and validated against correlative measurements from balloon-borne sondes and ground-based lidar networks at facilities like Ames Research Center and International Ozone Observatory sites.
Processed datasets were archived in federated repositories coordinated with National Aeronautics and Space Administration data centers and international archives accessed by researchers at institutions including Scripps Institution of Oceanography, University of Cambridge, and University of Tokyo. The SME archive has been used for reanalysis projects and cross-mission syntheses involving UARS, ERS-2, and Aura datasets.
The mission influenced subsequent mission design and instrument suites on projects such as UARS and Aura and informed policy-relevant assessments by the World Meteorological Organization and environmental science committees at United Nations Environment Programme. SME-derived insights advanced atmospheric chemistry theory at academic centers including Massachusetts Institute of Technology and University of California, Berkeley and contributed to operational algorithm development at NOAA and European Centre for Medium-Range Weather Forecasts. The mission legacy persists in long-term ozone records and methodological practices for limb occultation that underpin contemporary remote sensing efforts.