The solar X-ray photometer (SXP) was part of the SNOE mission, and measured the solar irradiance at wavelengths from soft X-ray to hard EUV (or “XUV”) portion of the solar spectrum. Each photometer channel consisted of a silicon photodiode; wavelength selection is accomplished by thin metallic films deposited directly onto the diode surface. A door with a fused silica window covered the diodes. When it was open, the diodes measure solar X-rays plus some visible light contamination. When it was closed, the X-rays were blocked and only the visible light was measured. By subtracting the door-closed measurement from the door-open measurement, the X-ray fluxes are obtained.