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.

SDO（太阳动力学观测站）的EVE（极端紫外变率实验）通过分析太阳的磁特征，对太阳极端紫外辐射亮度进行测量。该实验凭借其提升的光谱分辨率、时间采样率、准确度与精确度，将超越TIMED SEE、SOHO和SORCE XPS所进行的测量。EVE有助于科学家们深入理解太阳在驱动地球外部大气层中所扮演的角色。EUV辐射涵盖0.1-105纳米的波长范围，为地球热层加热和形成地球电离层提供了大部分能量。这一宽广的波长范围要求使用多个通道。EVE的关键要求包括以0.1纳米的光谱分辨率和20秒的时间间隔测量太阳EUV辐射光谱。这些要求推动了EVE的设计，包括阵列探测器与光栅光谱仪的结合，以便能够同时测量所有EUV波长。EVE的另一项关键要求是以25%或更高的精度测量EUV辐射，因此，在SDO任务期间， onboard校准通道与飞行前校准实验相结合。

EVE仪器体积相当庞大，其尺寸为100厘米（39英寸）长、61厘米（24英寸）宽、36厘米（14英寸）高，重量为61公斤（135磅）。其平均功耗为60瓦，但峰值可达137瓦。工程数据以每秒2千比特（kbps）的低速率输出，而科学数据则以每秒7兆比特（Mbps）的速度传输，以便每10秒下载一次MEGS CCD图像。

EVE仪器包含三个子系统：MEGS、ESP和EEB。

1. MEGS（多通道EUV光栅光谱仪）：由两套Rowland圆光栅光谱仪组成，用于测量5-105纳米光谱辐射亮度，具有0.1纳米的光谱分辨率和10秒的时间间隔。每套光谱仪都配备了来自麻省理工学院林肯实验室的背照式2048 x 1024 CCD相机。CCD电子箱（CEB）也是MEGS的一部分。MEGS拥有4个通道：MEGS-A：用于5纳米至37纳米范围的掠入射光栅光谱仪；MEGS-B：用于35纳米至105纳米范围的正常入射双光栅光谱仪；MEGS-SAM：与MEGS-A CCD配合使用的针孔相机，用于测量0.1纳米至7纳米范围内的单个X射线光子；MEGS-P：与MEGS-B的第一个光栅配合使用的光电二极管，用于测量明亮的H I莱曼-α发射。

2. ESP（EUV光谱光度计）：透射光栅光谱仪，用于测量17-38纳米范围内的4个波段，以及零级中的0.1-7纳米。ESP为MEGS的灵敏度变化提供校准，并具有更高时间采样率（0.25秒）。ESP与SOHO SEM仪器非常相似。

3. EEB（EVE电子箱）：用于控制MEGS和ESP仪器，并提供与SDO航天器之间的接口。