The SOLAR payload on the ISS.Fourth bridging operation.

The SOLAR payload, located on one of the four external platforms of the Columbus module on the International Space Station, is active since February 2008 and measures the solar spectral irradiance with two instruments : SOLSPEC which covers the spectral range of the Ultra-Violet (UV) to the near infrared and SOL-ACES, a set of spectrometers measuring the Extreme UV radiation (EUV).

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Due to the characteristics of the ISS orbit and the mechanical limitations for the platform, at most 20 minutes of measurements are possible per ISS revolution, and this for only 10 to 12 consecutive days per month. However, at the solstices, a small change of attitude of the ISS allows to bridge two of these so-called Sun Visibility Windows and thus to cover a full solar rotation which is about 27 days.

Now, around the solar maximum of Solar Cycle 24, four of these bridgings have been completed, the latest one lasted from June 29 to July 27 with a special attitude of the ISS between June 29 and July 10. All observations went according to schedule and no data at all were lost.

The scientific data are processed by the science teams at the Fraunhofer-Institut für Physikalische Messtechnik IPM (Germany), the Belgian Institute for Space Aeronomy (Belgium), and the “Laboratoire Atmosphères, Milieux, Observations Spatiales” (LATMOS, France). The rapid variations observed in the spectrum are especially important as they are correlated to the fluctuations of the solar input to the Earth system. In the case of EUV, the variations are much more important than in the visible and data of SOLAR are used to calculate the variation of the total electron content of the upper atmosphere.

These data are thus not only important for solar physics and earth climate, but they could also be used to determine upper atmospheric parameters directly relevant to both radio communications and the operation of Global Navigation Satellite Systems.