The primary instrument on Munin is MEDUSA (Miniaturized Electrostatic DUal-tophat Spherical Analyzer), a combined electron and ion spectrometer. The instrument sensor is provided by the Southwest Research Institute, San Antonio, Texas. Electrons and ions with energies up to 17 keV/q will be measured simultaneously, with a maximum time resolution of 4 energy sweeps per second for electrons, and 2 sweeps per second for ions. Particles are measured in 16 sectors in the plane of acceptance, which is aligned with the Earth's magnetic field.

Particles enter the spectrometer aperture at any angle in the plane of incidence, electrons and ions are then deflected into their respective spectrometer unit by a spherical electrostatic analyser. The particles hit a microchannel plate after being filtered in energy in the electrostatic analyser, the hits are counted by preamplifiers connected to registers, and the hits per sample interval are then further processed by the data processing unit (DPU).

The MEDUSA sensor represents a completely new development in terms of highly compact sensor design. MEDUSA has also been flown on the Swedish microsatellite Astrid-2, launched on December 10, 1998.

Wiev images of the Medusa instrument.

Dr. David Winningham at Southwest Research Institute

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