The Extreme Ultraviolet Spectrophotometer (ESP) instrument, part of the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) instrument suite is a direct descendent of the Solar and Heliospheric Observatory/Solar Extreme Ultraviolet Monitor (SOHO/SEM) instrument now orbiting around the First Lagrangian point (L1) between the Earth and Sun one million miles from Earth. ESP uses the same Extreme Ultraviolet (EUV) transmission grating technology developed at MIT that is used by SOHO/SEM. (Click on the images to enlarge)

SDO is the first mission for the NASA's Living with a Star (LWS) program. SDO was launched on Feb 11, 2010 at 10:23 am EST. The SDO mission will provide measurements and models of solar radiation and its dynamics, which affect Earth's space weather environment.

ESP with 5 wavelength bands covering 0.1nm-39 nm will provide a fast, stable and accurate data product with 0.25 second cadence for Space Weather and will serve as a stable reference for EVE's Multiple EUV Grating Spectrograph (MEGS) Spectrometers. The instrument is based on well proven and highly reliable optical elements including high ruling density transmission gratings (that are not susceptible to reflection degradation) and stable photodiode detectors. The ESP represents an evolution of the SEM with additional capabilities including coverage of more spectral lines, and the use of a quadrant detector in the central-order to provide in-flight pointing information.

The ESP instument configuration includes a high-voltage grid, a filter wheel with five filters, low-current electrometers, electrometer channel motherboard and an opto-mechanical assembly consisting of the diffraction grating, baffles, and the photo-diode detector assembly. All details of the ESP design and pre-flight calibrations are given in the Solar Physics (paper)