The Space Environmental Monitor (SEM-2) is a multi-channel, charged-particle spectrometer that 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 communication, high-altitude operations, damage to satellite circuits and solar panels, or cause changes in drag and magnetic torque on satellites.

SEM-2 consists of two separate sensor units (TED and MEPED) and a common Data Processing Unit (DPU). The Total Energy Detector (TED) measures electron and proton energy fluxes in the 0.05 to 20 keV energy range. The TED consists of eight Electrostatic Analyzers, that select particles according to their charge and energy, and which produce a pulse for each incident particle. The Medium Energy Proton and Electron Detector (MEPED) senses protons, electrons, and ions with energies from 30keV to levels exceeding 6.9MeV, using two proton telescopes with Solid State Detectors, two electron telescopes and four omni-directional sensors.

SEM Summary Budgets

SEM-2 is provided by NOAA and developed by Assurance Technology Corporation (formerly Panametrics), Waltham, Massachusetts, USA, under contract to NASA.