The ACE Magnetometer (MAG) experiment consists of two triaxial fluxgate magnetometers mounted remotely on booms extending beyond the spacecraft solar panels at four meters from the spacecraft center. Each identical sensor (M1, M2) has a wide dynamic range of sensitivity at +- 0.004 to +- 65536 nT and measures the three vector components of the magnetic field. Usage of twin magnetometer sensors for measurements of weak interplanetary magnetic fields is a proven approach based on experience from many past space missions. The MAG sensors were originally built as spares for the MFI instrument on the WIND spacecraft and have been given minor modifications for inclusion on ACE. Readout of MAG data includes three data types: (1) average magnetic field vectors from the primary and secondary sensors, (2) "Snap-Shot Memory" data, and (3) Fast Fourier Transform (FFT) data. The average vector readout includes 216 bps corresponding to six vectors per second. These vector readouts can be split between M1 and M2 in the ratios of 3:3, 5:1, or 6:0. The "Snap-Shot Memory" stores field vectors at the maximum sampling rate of 30 vectors per second and is read out at 48 bps. The FFT readout includes 17 seconds accumulation of vector data transformed into spectral matrices of the components and total magnitude at a transmission rate of 32 bps. Prof. Norman F. Ness of the Bartol Research Institute at the University of Delaware is the MAG Experiment Manager.

Instrument description

Description of the ACE magnetometer design and instrument characteristics, with links to data and other documentation

NSSDC's Master Catalog

Information about the Magnetometer (MAG) experiment on the ACE mission.

The Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) instrument sensors measure solar wind electrons at 1 - 900 eV energy and ions at 0.26 - 35 keV. The instrument consists of separate electron and ion analyzers originally built as spares for the Ulysses mission. The two sensors both utilizes curved-plate electrostatic analyzers (ESAs) consisting of spherical sections cut into sectors. Biased channel electron multipliers (CEMS) are spaced along the exit apertures of the ESAs for ion and electron detection. Different CEMs sample different portions of the fan-shaped fields of view. The ion sensor consists of a 105-degree bending angle ESA with an average radius of 100 mm and a plate spacing of 2.84 mm. Sixteen CEMs contiguously spaced along the exit gap of the ESA give about 5-degree polar angular resolution over the approximately 70-degree opening angle of the acceptance fan. The electron sensor consists of a 120-degree bending angle ESA with an average radius of 41.9 mm and a plate spacing of 3.5 mm. Seven large-funnel CEMs along the exit gap give about 20-degree angular resolution over a 160-degree fan angle. The sensor geometric factors are 0.002 cm2-sr for isotropic response and 0.009 cm2 for unidirectional. Energy resolution is five percent for ions and twelve percent for electrons. SWEPAM data consists of ion and electron rates collected at each energy/charge (E/Q) step, polar lock direction, and azimuthal spin direction. A single spacecraft spin period of 12 seconds is sufficient for accumulation of count matricies to fully calculate the electron and ion distribution functions from which bulk moments (solar wind speed, density, temperature) can be calculated by ground data processing. Accumulated counts will actually be summed over one-minute intervals for increased statistical accuracy and for reduction of telemetry requirements. Limited data from single spins will be provided for timing of the passage of transient solar wind structures.

SWEPAM home page at LANL

Information about the SWEPAM instrument, with links to data and other documentation

NSSDC's Master Catalog

Information about the Solar Wind Electron, Proton and Alpha Monitor (SWEPAM) experiment on the ACE mission.

The magnetic field experiment on WIND provides data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) on the WIND Spacecraft is a boom-mounted dual triaxial fluxgate magnetometer and associated electronics. The dual configuration provides redudancy and also permits accurate removal of the dipolar portion of the spacecraft magnetic field. The instrument provides:

(1) near real-time data at nominally one vector per 92 s as key paramter data for broad dissemination, (2) rapid data at 10.9 vectors/s for standard analysis, (3) occasionally, snapshot (SS) memory data and Fast Fourier Transform data (FFT), both based on 44 vectors/s.

These measurements are precise (0.025%), accurate, ultra-sensitive (0.008 nT/step quantization), and where the sensor noise level is <0.006 nT r.m.s for 0-10 Hz. The digital processing unit utilizes a 12-bit microprocessor controlled analogue-to-digital converter. The instrument features a very wide dynamic range of measurement capability, from 4 nT up to 65 536 nT per axis in eight discrete ranges. (The upper range permits complete testing in the Earth's field.) In the FFT mode power spectral density elements are transmitted to the ground as fast as once every 23 s (high rate), and 2.7 min of SS memory time series data, triggered automatically by pre-set command, requires typically about 5.1 hours for transmission. Standard data products are the following vector field averages: 0.0226 s (detail data from SS), 0.092 s ('detail' in standard mode), 3 s, 1 min, and 1 hour, in both GSE and GSM coordinates, as well as the FFT spectral elements. High instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs.

The instrument was turned on on 1994-11-12.

References: Lepping, R. P., et al., The WIND Magnetic Field Investigation, Space Science Reviews, 71, 207-229, 1995.

WIND Magnetic Field Investigation (MFI) Home Page

A web site hosting WIND MFI instrument information as well as web utilities for plotting and downloading data

User will acknowledge the WIND MFI instrument team in any publication resulting from the use of these data.

This investigation is designed to provide complete, accurate specification of solar wind flow parameters in real time. The instrument is a six-axis ion-electron spectrometer which provides three-dimensional velocity distribution functions for ions and electrons, with high time resolution. The energy range covered extends from 7 eV to 30 keV for electrons in four different modes, and from 30 eV to 30 keV in four different ion modes. In addition, two Faraday cups are used to obtain three-dimensional measurements of ions in 15-s periods, in the energy range 5 eV to 5 keV.

NSSDC's Master Catalog

Information about the Solar Wind Experiment (SWE) experiment on the Wind mission.

The magnetic field experiment on the IMP-8 spacecraft utilizes a tri-axial fluxgate (saturable inductor) magnetometer. The instrument originally had three, automatically determined, ranges, ±12 nT, ±36 nT, and ±108 nT, full scale. Because of a range-change circuit failure occurring in early July 1975, the experiment was commanded into a fixed ±36 nT range on July 11, 1975 at 12:55:09 UT and has been in that range ever since. The measurements are A-to-D converted onboard, to an 8-bit resolution, yielding ±0.14 nT quantization sensitivity, which is larger than the intrinsic sensor noise level of 0.025 nT RMS. The data from the two-bit (per component) adaptive delta modulator, incorporated into the instrument, and applied to the intrinsic sample rate of 25 vectors/sec., was never utilized, and hence the rate of the full (8-bit) vector words, which occur every 320 ms, represents the effective sample period of the instrument. The sampling rate is synchronized to the spacecraft clock; the basic spacecraft clock frequency is 6.4 kHz. The sensor unit is mounted on the end of a boom approximately 4 m from the center of the spacecraft.

IMP-8 Magnetometer Home Page

A web site hosting IMP-8 magnetic experiment instrument information as well as web utilities for plotting and downloading data.

NSSDC's Master Catalog

Information about the Magnetic Field Experiment experiment on the IMP 8 mission.

User will acknowledge the IMP-8 magnetometer team in any publication resulting from the use of these data.

A modulated split-collector Faraday cup, perpendicular to the spacecraft spin axis, was used to study the directional intensity of positive ions and electrons in the solar wind, transition region, and magnetotail. The collector plate split is perpendicular to the spacecraft spin axis in order to measure the flow angle of the ions in a meridional plane; the flow angle in the spacecraft equatorial plane is determined from the fluxes measured as the spacecraft rotates.

Electrons are measured using 21 logarithmically-spaced energy windows covering the energy/charge range between 23 and 1935 volts. Positive ions are studied using 24 energy windows covering the range between 50 and 7000 volts.

The instrument has three operating modes. The tracking mode yields the best time resolution which is about 1 minute. A single energy window is used during a spacecraft rotation. The ion spectrum is obtained in eight spacecraft revolutions using a subset of the energy windows that track the peak of the solar wind. In this mode, fluxes are measured during 11.25-degree sectors of the spacecraft spin while the instrument is looking within the 90 degree sector centered on the sun direction and during 45 degree sectors for the remainder of the rotation. The other modes yield a spectrum using all 24 windows (with the same angular sectors described above) or a spectrum that results from integrating the observed fluxes over 45 degree sectors for the entire spacecraft rotation.

Electron data are obtained in all modes, but are not usually analyzed.

Parameters derived on a routine basis are proton velocity, number density, and temperature (most probable thermal speed). Those parameters are obtained from a non-linear, least-squares fit to the observed fluxes using a convected, isotropic Maxwellian model.

Key Parameters for the Plasma instrument are computed at MIT using Level Zero data that are staged to the ISTP/CDHF approximately two weeks after being received on Earth. Thus the plasma instrument's Key Parameters lag real time by something greater than 2 weeks, but less than four.

IMP 8 Home Page

NSSDC's Master Catalog

Information about the Solar Plasma Faraday Cup experiment on the IMP-J mission.

The objective of this experiment is to measure the magnetic field variation of the magnetotail in the frequency below 50 Hz. The MGF experiment consists of dual three-axis fluxgate magnetometers and a three-axis search coil magnetometer. Triad fluxgate sensors, which utilize a ring core geometry, are installed at the end and middle of a 6 m deployable mast. Three search coils are mounted approximately one-half of the way out on another 6 m boom together with search coils for the VLF wave in the PWI system.

The fluxgate magnetometers are of standard design and consist of an amplifier, filter, phase sensitive detector, integrator, and a voltage-current convertor. The fluxgate magnetometers operate in seven dynamic ranges to cover various regions of the Earth's magnetosphere and the solar wind: +/-16 nT, +/-64 nT, +/-256 nT, +/-1024 nT, +/-4096 nT, +/-16384 nT, and +/-65536 nT, and supply 16 vectors/sec.

The automatic range control of the fluxgate magnetometers failed in 1999 so the observable range was manually fixed in the +/-256 nT where it has remained ever since. On November 23, 2006, the fluxgate magnetometer at the end of the boom failed and data from the second magnetometer at the middle of the boom has been used ever since. Neither of the above changes substantially affect the data.

The search coil magnetometer system consists of three sensors, preamplifier, amplifier, filter, multiplexer, and an A/D converter. The search coil magnetometers operate in a frequency range of 0.5 kHz to 1 kHz, and supply 128 vectors/sec. The fluxgate magnetometer operates in both real time and record modes, while the search coil data are used only in real time mode.

NSSDC's Master Catalog

Information about the Magnetic Fields Measurement (MGF)

The objective of the Comprehensive Plasma Instrumentation (CPI) investigation is to make comprehensive observations of the three-dimensional velocity distribution functions of electrons and positive ions, with identification of ion species. The instrument contains three sets of quadrispherical analyzers with channel electron multipliers. These three obtain three-dimensional measurements for hot plasma and solar wind electrons, for solar wind ions, and for positive-ion composition measurements. The positive-ion composition measurement of the Ion Composition (IC) analyzer includes five miniature imaging mass spectrometers at the exit aperture of the analyzer, and covers masses from 1 to 550 u/Q at 100 eV, and 1 to 55 u/Q at 10 keV. The Hot Plasma (HP) analyzer measures electrons and ions in the range 1-50,000 eV/Q. The Solar Wind (SW) analyzer measures ions from 150 to 7,000 eV/Q. Sequencing of the energy analyzers and mass spectrometers, and other control functions, are provided by two microprocessors.

NSSDC's Master Catalog

Information about the Comprehensive Plasma Instrument (CPI)