Extreme Ultraviolet Photometer System (XPS)
Rarely do these shorter wavelengths penetrate the lower layers of the atmosphere, so they have little effect anywhere below 70 kilometers in altitude where weather develops and life is found. These wavelengths do, however, impact the very outermost regions of the atmosphere such as the mesosphere, the thermosphere, and the ionosphere. Changes in these wavelengths due to solar cycles can affect the chemical composition and the temperature of these regions, which in turn can disrupt satellite operations and radio and satellite communications.
The readings can also give scientists detailed information about what goes on in the Suns atmosphere. The Suns atmosphere consists of two zones known as the corona and the transition zone. The corona is a cloud of ions that burns at 1 million degrees Celsius, or roughly 200 times hotter than the temperature at the surface of the Sun. Between the Sun and the corona is a transition zone. Though the corona and the transition zone have been studied in increasing detail since the 1970s, their complex variations during the solar cycle are not adequately characterized. SORCE will provide further insight into these fluctuations in the outer solar atmosphere. The 1-31 nm range of XPS is sensitive to changes in the corona, and the Lyman-alpha monitors the transition zone.
Calibration of the XPS will be completed in part by the six diodes that do not take daily measurements. Three of these diodes will not be covered by filters, and they will be used to check on the condition of the silicon window that covers the photodiodes. The three remaining diodes will be covered by filters, and they will take redundant measurements of the Sun once a week. These readings will be compared to those taken daily by the six diodes measuring ultraviolet and x-ray radiation. Finally, sub-orbital flights will be launched once a year with identical XPS photodiodes on board. By contrasting these measurements taken by the sub-orbital flights with those of the instrument aboard SORCE, the scientists should be able to tell if the SORCE instruments performance has changed. If so, they can then make the compensating adjustments to the data they receive.
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