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Laboratory for Atmospheric and Space Physics


The XPS measures the solar soft x-ray (XUV) irradiance from 1 to 34 nm and the bright hydrogen emission at 121.6 (H I Lyman-alpha). The solar XUV radiation is mostly emitted from the hot, highly-variable corona of the Sun, and these high-energy photons are a primary energy source for heating and ionizing Earth’s upper atmosphere. Of all the SORCE instruments, the XPS is most sensitive to flare events on the Sun as the solar XUV radiation often changes by a factor of 2 to 10, or more, during flares.

Table 1: XPS Properties

Instrument Type Filter Photometer
Wavelength Range 1-27 nm, 121-122 nm
Wavelength Resolution 1-10 nm
Optics Thin Film Filters (deposited on Si photodiodes) and Interference Filter for 121.5nm channel
Detector 12 Si photodiodes: 8 XUV, 1 Ly-alpha, 3 bare
Absolute Accuracy 12-24%
Long-term Accuracy 1%/year
Field-of-View 4° cone
Dimensions (H×W×D) (without GCI) 15.6 cm × 18.7 cm × 17.2 cm
Mass (with GCI) 3.6 kg
Orbit Average Power 9 W
Peak Power 14 W peak (~30 sec/orbit)
Orbit Average Data Rate 0.3 kbits/s
Redundancy 3 redundant XUV diodes
Heritage TIMED SEE, SNOE, and rocket XPS
In-flight Cal Redundant Channels, TIMED SEE claibration rockets
Pre-flight Cal. Std. NIST SURF-III, ref. Si diode