The XRS is an x-ray telescope that observes and measures solar x-ray emissions in two
ranges—one from 0.05 to 0.3 nanometers (nm) and the second from 0.1 to 0.8 nm. In real-time,
it measures the intensity and duration of solar flares in order to provide alerts and warnings of
potential geophysical responses, such as changes in ionospheric conditions, that can disrupt
radio communications and Global Positioning System (GPS) signals. XRS data is also used to
estimate solar flare parameters such as rise-time (how quickly a flare grows) and the length and
temperature of a flare for use in energetic proton predictions.

The five-channel EUV telescope is new on the GOES-N,O,P satellites. It measures solar
extreme ultraviolet energy in five wavelength bands from 10 nm to 126 nm. The EUV sensor
provides a direct measure of the solar energy that heats the upper atmosphere and creates the
ionosphere. Changes in solar EUV output can change the density of the upper atmosphere by a
factor of 10, which will cause increased drag for satellites in low-Earth-orbit.
Similarly, these changes in EUV level can increase the density of the ionosphere by a
factor of 10, which will affect radio communications and satellite navigation.

Both the XRS and EUV are provided by Assurance Technology Corporation, and
are part of the sun-observing package mounted on the solar panel yoke
assembly. The entire package (including the SXI) continually points at the sun by
using a Precision Sun Sensor (PSS) to control the solar panels to track the sun in
azimuth and the x-ray positioner (XRP) to track the sun in elevation.