Geostationary-Orbit Trapped Radiation Environment Facility
The facility's primary asset is a database that provides a broad compilation of information about the ambient radiation environment at geostationary orbit. Knowledge of the radiation environment at geostationary orbit is important to spacecraft design, communications, and operations, and to such scientific purposes as understanding the structure and dynamics of the earth's magnetosphere.
Data have been available from several different satellites since 1976, with typically more than one operating at any given time. The geostationary-orbit, energetic-particle detectors aboard first generation of these satellites (prior to 1989) were called CPAs (charged particle analyzers), and similar instrumentation on the later generation (post-1989) were called SOPAs (synchronous orbit particle analyzers). Each of the post-1989 satellites also included a lower-energy instrument called MPA (magnetospheric plasma analyzer). While these instruments are primarily environmental monitors for the spacecraft on which they reside, they also generate a good deal of the geostationary-orbit, charged-particle data available to the community of users of such data. They provide information about the charged-particle distributions at the spacecraft every 10 seconds.
Currently we continue to receive particle data from five SOPA and MPA detectors, and archival data from 1976 to the present is available from our web sites: Geosynchronous EP Data and MPA data. At the latter site it is possible to view daily plots of electron and proton fluxes and request digital data for downloading to your computer. Investigators concerned with satellite anomalies, design, magnetospheric dynamics, and space weather are likely users of the database. [A satellite placed in a geostationary orbit appears to remain above a fixed point on the earth's geographic equator because it has an orbital speed exactly matched to the earth's rotation at that point. The satellite's stationary position, as seen from earth, gives it important practical applications in such diverse fields as weather observation, communication, navigation, and military use.]
The CPA detectors cover electrons in 12 channels over the range of energies from 30 to 2000 kiloelectron volts (keV) and in 26 ion channels covering the range of about 100 keV to 160 million electron volts (MeV).
The SOPA detectors monitor not only electrons (50 keV to 2 MeV) and protons (50 keV to 50 MeV), but also helium (0.5 MeV to 1.5 MeV), carbon + oxygen + nitrogen (1.5MeV to 3.5 MeV), carbon (5 MeV to 13 MeV), nitrogen (6 MeV to 14 MeV), and oxygen (7.2 MeV to 15 MeV). In addition, the SOPAs have the ability, in principal, to monitor ion composition by means of a dual parameter pulse-height-analysis scheme. More detailed descriptions of the CPA and SOPA instruments can be found here.
The MPA detectors measure the full 3-dimensional velocity distribution of ions and electrons over the range 1 eV to 45 keV, with an acquisition time of 10 s and a repetition rate of one every 86 sec. A more complete description of the instrument is provided by Bame et al. [Rev. Sci. Instr., 64, p. 1026, 1993]. Numerically integrated moments of the distribution are routinely computed and are also available on the MPA website.
Last Update: 23 January 2007