spase://SMWG/Instrument/SDO/EVE

The SDO (Solar Dynamics Observatory) EVE
ExtremeUltraviolet Variability Experiment) measures the solar
extreme ultraviolet irradiance variations based on the Sun's
magnetic features. With improved spectral resolution,
temporal cadence, accuracy, and precision, data will
supersede measurements made by TIMED SEE, SOHO and SORCE XPS.
It helps scientists to understand the Sun's role in driving
the outer atmosphere of Earth. The EUV radiation includes
the 0.1-105 nm range, which provides the majority of the
energy for heating Earth's thermosphere and creating Earth's
ionosphere. This wide spectral range requires the use of
multiple channels. Some key requirements for EVE are to
measure the solar EUV irradiance spectrum with 0.1 nm
spectral resolution and with 20 sec cadence. These drive the
EVE design to include grating spectrographs with array
detectors so that all EUV wavelengths can be measured
simultaneously. Another key requirement for EVE is to
measure the EUV radiation with an accuracy of 25% or better,
thus on-board calibration channels are included to go with
underflight calibration experiments to be conducted during
the SDO mission.

The EVE instrument is a fairly large instrument with its
size being 100 cm (39") long by 61 cm (24") wide by 36 cm
(14") high and weighing 61 kg (135 lbs). Its average power
is 60 Watts, but can peak up to 137 Watts. The engineering
data are output at a low rate of 2 kilobits per sec (kbps),
but the science data rate is at 7 megabits per sec (Mbps)
in order to download both MEGS CCD images every 10 seconds.

There are three instrument subsystems, MEGS, ESP, and EEB:

1. MEGS (Multiple Euv Grating Spectrograph): set of 2
   Rowland-circle grating spectrographs that measure the
   5-105 nm spectral irradiance with 0.1 nm spectral
   resolution and with 10-second cadence. Each spectrograph
   uses a back-illuminated 2048 x 1024 CCD camera from MIT
   Lincoln Laboratory. The CCD Electronics Box (CEB) is also
   part of MEGS. MEGS has 4 channels: MEGS-A: grazing incidence
   grating spectrograph for 5 nm to 37 nm range; MEGS-B: double
   normal-incidence grating spectrograph for 35 nm to 105 nm;
   MEGS-SAM: pinhole camera used with MEGS-A CCD to measure
   individual X-ray photons in the 0.1 nm to 7 nm range;
   MEGS-P: photodiode used with the first grating in MEGS-B
   to measure the bright H I Lyman-alpha emission

2. ESP (Euv SpectroPhotometer): transmission grating
   spectrograph that measures 4 bands in the 17-38 nm range
   and also 0.1-7 nm in zeroth order. ESP provides calibrations
   for MEGS sensitivity changes and higher time cadence
   (0.25-second). The ESP is very similar to the SOHO SEM
   instrument.

3. EEB (EVE Electronics Box): electronics that control the
   MEGS and ESP instruments and provides an interface to/from
   the SDO spacecraft.