Science
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 |
