ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-19-593-2001 The MEDUSA electron and ion spectrometer and the PIA ultraviolet photometers on Astrid-2 Norberg O. 1 Winningham J. D. 2 Lauche H. 3 Keith W. 2 Puccio W. 1 Olsen J. 1 Lundin K. 1 Scherrer J. 2 Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden Southwest Research Institute, P. O. Drawer 28510, San Antonio, Texas 78228-0510, USA Max-Plank-Institut für Aeronomie, Postfach 20, D-37189 Katlenburg-Lindau, Germany 30 06 2001 19 6 593 600 Copyright: © 2001 O. Norberg et al. 2001 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/19/593/2001/angeo-19-593-2001.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/19/593/2001/angeo-19-593-2001.pdf

The miniature electron and ion spectrometer MEDUSA on Astrid-2 consists of two "top-hat"-type spherical electrostatic analyzers, sharing a common top-hat. Fast energy sweeps (16 electron sweeps and 8 ion sweeps per second) allow for very high temporal resolution measurements of a two-dimensional slice of the particle distribution function. The energy range covered, is in the case of electrons, 4 eV to 22 keV and, in the case of ions, 2 eV to 12 keV. MEDUSA is mounted with its aperture close to the spin plane of Astrid-2, which allows for good pitch-angle coverage when the local magnetic field is in the satellite spin plane. The PIA-1/2 spin-scanning ultraviolet photometers measure auroral emissions. Using the spacecraft spin and orbital motion, it is possible to create two-dimensional images from the data. Spin-scanning photometers, such as PIA, are low-cost, low mass alternatives to auroral imagers, but place constraints on the satellite attitude. Data from MEDUSA are used to study processes in the auroral region, in particular, electrodynamics of aurora and "black aurora". MEDUSA is also a technological development, paving the way for highly capable, miniaturized particle spectrometers.<br><br><b>Key words. </b>Ionosphere (instruments and techniques) – Magnetospheric physics (auroral phenomena; instruments and techniques)