Magnetic Field Experiment on the Freja Satellite

Freja is a Swedish scientific satellite mission to study fine scale auroral processes. Launch was October 6, 1992, piggyback on a Chinese Long March 2C, to the present 600 × 1750 km, 63° inclination orbit. The JHU/APL provided the Magnetic Field Experiment (MFE), which includes a custom APL-designed Forth language microprocessor. This approach has led to a truly generic and flexible design with adaptability to differing mission requirements and has resulted in the transfer of significant ground analysis to on-board processing. Special attention has been paid to the analog electronic and digital processing design in an effort to lower system noise levels, verified by inflight data showing unprecedented system noise levels for near-Earth magnetic field measurements, approaching the fluxgate sensor levels. The full dynamic range measurements are of the 3-axis Earth’s magnetic field taken at 128 vector samples s-1 and digitized to 16 bit resolution, primarily used to evaluate currents and the main magnetic field of the Earth. Additional 3-axis ‘AC channels are bandpass filtered from 1.5 to 128 Hz to remove the main field spin signal, the range is ±650 nT. These vector measurements cover Pc waves to ion gyrofrequency magnetic wave signals up to the oxygen gyrofrequency (~40 Hz). A separate, seventh channel samples the spin axis sensor with a bandpass filter of 1.5 to 256 Hz, the signal of which is fed to a software FFT. This on-board FFT processing covers the local helium gyrofrequencies (~160 Hz) and is plotted in the Freja Summary Plots (FSPs) along with disturbance fields. First data were received in the U.S. October 16 from Kiruna, Sweden via the Internet and SPAN e-mail networks, and were from an orbit a few hours earlier over Greenland and Sweden. Data files and data products, e.g., FSPs generated at the Kiruna ground station, are communicated in a similar manner through an automatic mail distribution system in Stockholm to PIs and various users. Distributed management of spacecraft operations by the science team is also achieved by this advanced communications system.

[1]  M. H. Acuna,et al.  The MAGSAT vector magnetometer: A precision fluxgate magnetometer for the measurement of the geomagnetic field , 1978 .

[2]  S. Grahn,et al.  The Freja science mission , 1994 .

[3]  B. Mauk,et al.  Magnetospheric electric fields and currents , 1987 .

[4]  L. Zanetti,et al.  Large‐scale characteristics of magnetospheric equatorial currents , 1990 .

[5]  M. Acuna,et al.  Fluxgate magnetometers for outer planets exploration , 1974 .

[6]  R. Huffman,et al.  Multiple auroral arcs and Birkeland currents: evidence for plasma sheet boundary waves , 1986 .

[7]  M. Acuna,et al.  Harmonically structured ULF pulsations observed by the AMPTE CCE Magnetic Field Experiment , 1986 .

[8]  W. J. Burke,et al.  Electrodynamic structure of the late evening sector of the auroral zone , 1980 .

[9]  R. Lundin,et al.  Observations of large‐scale Birkeland currents with Viking , 1987 .

[10]  R. Erlandson,et al.  Magnetic-field fluctuations from 0 to 26 Hz observed from a polar-orbiting satellite , 1989 .

[11]  H. Koskinen,et al.  The Freja Hot Plasma Experiment—Instrument and first results , 1994 .

[12]  John Hayes,et al.  An architecture for the direct execution of the Forth programming language , 1987, ASPLOS 1987.

[13]  B. Anderson,et al.  Auroral currents during the magnetic storm of November 8 and 9, 1991: Observations from the Upper Atmosphere Research Satellite Particle Environment Monitor , 1993 .

[14]  Ben Ballard.  FORTH direct execution processors in the Hopkins ultraviolet telescope , 1984 .

[16]  R. Erlandson,et al.  Viking magnetic and electric field observations of Pc 1 waves at high latitudes , 1990 .

[17]  D. Gordon,et al.  Recent advances in fluxgate magnetometry , 1972 .

[18]  L. Blomberg,et al.  Plasma characteristics determined by the Freja electric field instrument , 1994 .

[19]  B. Anderson,et al.  Pc1 pulsations observed by AMPTE/CCE in the Earth's outer magnetosphere , 1990 .

[20]  R. Lundin,et al.  Resonant geomagnetic field oscillations and Birkeland currents in the morning sector , 1988 .