The Extreme Solar Ultraviolet Monitor (ESUM) experiment made absolute broadband
spectro-radiometric measurements of the solar EUV flux from 200 A to Lyman-alpha at 1216 A and
made precise measurements of the temporal variability. The instrument consisted of two identical
windowless EUV photodiodes with aluminum oxide cathodes and a filter wheel containing two sets of
unbacked metallic filters (aluminum, tin, indium) and an open position. A visible light diode
measured the pinhole transmittance of the filters to determine the white light background. The
tilt angle of the instrument relative to the +Z spacecraft axis was optimized for the maximum
viewing time of the sun in both spinning and despun spacecraft modes. The instrument field of view
was 60 deg. The nominal bandwidths in Angstroms for 50% of the signal were 270 to 550, 570 to 584,
800 to 935, and 1216 A. More experiment details can be found in D. F. Heath and J. F. Osantowski,
Radio Sci., v. 8, n. 4, p. 361, 1973.