Overview of the Solar Radiation and Climate Experiment (SORCE) Seventeen-Year Mission

Abstract

The Solar Radiation and Climate Experiment (SORCE) was a NASA mission that operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). Three important accomplishments of the SORCE mission are i) the continuation of the 42-year-long TSI climate data record, ii) the continuation of the ultraviolet SSI record, and iii) the initiation of the near-ultraviolet, visible, and near-infrared SSI records. All of the SORCE instruments functioned well over the 17-year mission, which far exceeded its five-year prime mission goal. The SORCE spacecraft, having mostly redundant subsystems, was also robust over the mission. The end of the SORCE mission was a planned passivation of the spacecraft following a successful two-year overlap with the NASA Total and Spectral Solar Irradiance Sensor (TSIS) mission, which continues the TSI and SSI climate records. There were a couple of instrument anomalies and a few spacecraft anomalies during SORCE’s long mission, but operational changes and updates to flight software enabled SORCE to remain productive to the end of its mission. The most challenging of the anomalies was the degradation of the battery capacity that began to impact operations in 2009 and was the cause for the largest SORCE data gap (August 2013 – February 2014). An overview of the SORCE mission is provided with a couple of science highlights and a discussion of flight anomalies that impacted the solar observations. Companion articles about the SORCE instruments and their final science data-processing algorithms provide additional details about the instrument measurements over the duration of the mission.

Characteristics of solar-irradiance spectra from measurements, modeling, and theoretical approach

“…The composite SORCE SSI data product, downloaded from the LISIRD web page ( http://lasp.colorado.edu/lisird ) in January 2020, was used in this analysis. Figure 2 shows time series from instruments aboard SORCE 17 for selected wavelengths from the extreme ultraviolet to the infrared. The selected wavelengths are 1.5 nm, 16.5 nm, Ly α (Lyman α at 121 nm), 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 500 nm, 1000 nm, 2000nm, and 2400 nm.…”

“…Likely, this variation is of instrumental origin. Above 300 nm, SSI variations are from instrumental origin rather than solar origin 17 .…”

“… SOLAR3 44 based on reprocessed SOLSPEC-ISS measurements. SOlar Radiation and Climate Experiment (SORCE 17 ): EUV to IR daily average irradiances. X-ray Photometer System 45 version 11, SOLar-Stellar Irradiance Comparison Experiment 45 version 17, and Spectral Irradiance Monitor 46 version 25 are used in this study.…”

“…The far ultraviolet (FUV, 115–200 nm) range has been regularly observed since the early 1980’s with only a small gap between the Solar Mesosphere Explorer (SME 15 ) and the Upper Atmosphere Research Satellite (UARS 16 ) missions. With the end of the Solar Radiation and Climate Experiment (SORCE 17 ) mission in January 2020, the only available FUV data now come from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED 18 ) mission. When TIMED (launched in 2002) ends, there will be a gap in FUV observations.…”

Universal Scaling Laws for Solar and Stellar Atmospheric Heating

“…To measure the X-ray and Extreme UV fluxes, we used the spectral irradiance data obtained by the XUV Photometer System (XPS; 3 Since its launch in 2003, the spacecraft and the instruments were overall stable and well calibrated, but the degradation of the battery capacity caused some observation gaps (Woods et al 2021). The daily spectral irradiance data of SORCE/XPS (level 4, version 12), which covers the wavelengths from 1 to 400 Å with a spectral resolution of 1 Å, were used to measure the fluxes of X-ray 5.2-124 Å (the ROSAT heritage band ;Truemper 1982;Güdel 2007), Fe XV 284 Å, Fe XIV 211 Å, Fe XII 193+195 Å (combined), and He II 256 Å.…”