BackForwardInstrument:  MEP-i 

Instrument details
Acronym MEP-i
Full name Medium-energy particle experiments - ion mass analyzer
Purpose Measurement of medium-energy ions through the magnetosphere, specifically the Van Allen belts
Short description Spectrometer to observe ions in the energy range 10-200 keV. Detailed description not yet available
Background Part of a package to measure low, medium, high and extremely-high energy electrons (LEP-e, MEP-e, HEP-e and XEP-e) and low and medium energy ions (LEP-i and MEP-i)
Scanning Technique Volumetric exploration of the magnetosphere as the satellite travels along the HEO with perigee 300 km and apogee 30,000 km whilst spinning at 1 round / 8 s
Coverage / Cycle Full magnetospheric volume, more frequently in low-middle latitudes, consistently with the 31° orbital inclination
Mass Power Data Rate


Providing Agency JAXA
Instrument Maturity Flown on an R&D satellite
Utilization Period: 2017 to 2033
Last update: 2021-12-16
Detailed characteristics
Satellites this instrument is flying on

Note: a red tag indicates satellites no longer operational, a green tag indicates operational satellites, a blue tag indicates future satellites

Instrument classification
  • Solar and space environment monitors
  • Energetic particle spectrometer
WIGOS Subcomponents
  • Subcomponent 2
  • Magnetospheric energetic particles and magnetometers
  • Proton sensor [cross magnetosphere]
  • Alpha-particle sensor [cross magnetosphere]
  • Heavy ion sensor [cross magnetosphere]
  • Subcomponent 3
  • Neutral and Ion Mass Spectrometer
  • Heavy ions mass spectrometer [from LEO and HEO]
Mission objectives
Primary mission objectives
  • Alpha particles differential directional flux
  • Heavy ion flux energy and mass spectrum
  • Proton differential directional flux
Evaluation of Measurements

The following list indicates which measurements can typically be retrieved from this category of instrument. To see a full Gap Analysis by Variable, click on the respective variable.

Note: table can be sorted by clicking on the column headers
Note: * Primary mission objective.
VariableRelevance for measuring this variableOperational limitationsExplanation
Proton differential directional flux*2 - very highNo specific limitation.Magnetosphere, low and medium energy (up to 1000 keV)
Alpha particles differential directional flux*2 - very highNo specific limitation.Interplanetary space. Low-medium energy range (<10 up to 100 MeV/n)
Heavy ion flux energy and mass spectrum*2 - very highNo specific limitation.Cross-magnetosphere. Low-medium energy range (<10 up to 100 MeV/n)