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SEM photo

The SEM/2 is a spectrometer and provides measurements to determine the intensity of the Earth's radiation belts and the flux of charged particles at the satellite altitude. It provides knowledge of solar terrestrial phenomena and also provides warnings of solar wind occurrences that may impair long-range communications, high-altitude operations, damage to satellite circuits and solar panels, or cause changes in drag and magnetic torque on satellites.

The SEM/2 consists of two separate sensor units and a common Data Processing Unit (DPU). The sensor units are the Total Energy Detector (TED) and the Medium Energy Proton and Electron Detector (MEPED).

The DPU serves as the interface between the sensors and the spacecraft. The TED senses and quantifies the intensity in the sequentially selected energy bands. The particles of interest have energies ranging from 0.05 keV to 20 keV. The MEPED senses protons, electrons, and ions with energies from 30 keV to levels exceeding 6.9 MeV.


SEM-2 Units
Performance Requirements
Energy Levels (keV)
Field of View
Determine heat energy input into upper atmosphere from absorption of electrons, protons and positive ions.
Electrons: 0.05 keV to 20 keV

Protons: 0.05 keV to 20 keV
Two at 15 degrees full angle,

-x -x + 30
Same as TED
> 03 integral
> 100 integral
> 300 integral
Combine outputs into a 2-second, 40-word format. Provide command, calibrate and timing interfaces.
System Summary (Maximums)
Mass: 18 kg
Power: 10 Watts
Volume: 0.0186 m3
Telemetry: Two (8-bit) words/TIP minor frame

Source: NOAA KLM User's Guide

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Goddard Space Flight Center