Latest News Overview Mission
Spacecraft Scientific
Mission &

MAM Magnetic Field
DC to 64 Hz
Flux-Gate Magnetometers
on 1.8-m Booms
128 Samples/s
EDI Electric Field
DC to 25Hz
Electron Beam Sensing
2 Guns/Detectors
Energy 0.5/1.0 keV
Currents < 1µA
3DA 3D Electron & Ion
and Moments
10eV - 25 keV
Top-Hat E/q Analyzers
24 Energy Sweeps/Spin
8 Polar-Angle Channels
EPI Electrons & Ions
20-225/400 keV
16 Channels
Array of Solid-State
ICI H+,He+, He++, O+
3D Distributions
and Moments
ToF Spectrometer
with E/q Analysis
and RPA at Front
20kV Post-Acceleration
PCD Control of
Indium Ion Emitters
Currents < 50µA
Fixed or Variable
SFD Electrons
> 0.26 MeV
> 6.3 MeV
3 Scintillating Fibers
Photo-Diodes for


The science instruments on board EQUATOR-S will measure the ambient magnetic and electric fields and the density, velocity, temperature and composition of the charged particles that surround the spacecraft. Total data rates can be switched between a low rate (LR) of 32 kbps and a high rate (HR) of 131 kbps. Table 2 lists the instruments and some of their key properties. Measurements of high-frequency electric fields had to be sacrificed because the high spin-rate, low mass, and intended simplicity of the spacecraft ruled out the extension of long booms needed for such measurements. Although this restricts the measurement of the electromagnetic wave-field to below 50 Hz, such a compromise was considered acceptable since the processes effecting plasma transport across boundaries appear to involve field fluctuations at lower frequencies, near the proton gyrofrequency.

Magnetic Field Instrument (MAM)

The magnetic field instrument consists of three-axes flux-gate magnetometers, one mounted at the end of a 1.8-m boom, the other 50 cm further inboard, to reduce (and determine) the amount of interference from the spacecraft. The sampling rate is 128 vectors/s when only one of the magnetometers is utilized, and 64 vectors/s when both are utilized. Resolution is 16 bits, and ranges can be selected (automatically or manually) in steps of 4, between 250 and 64000 nT.

W. Baumjohann (MPE Garching, Germany) is the Lead Investigator (LI).

First measurement (December 12, 1997).

Electron Drift Instrument (EDI)

The electron drift instrument measures the displacement of a weak (< 1 µA) beam of test electrons, after one gyration in the ambient magnetic field, that is induced by electric fields or magnetic gradients. This displacement causes the beam to return to a detector on the spacecraft only when emitted in one of two precisley determined directions. By employing two beams and two detectors, these directions can be monitored continuously and the displacement obtained by triangulation. For small magnetic fields the triangulation degenerates and the displacement is obtained instead from the difference in the travel times of the electrons in the two beams. As a by-product, the measured times-of-flight provide a precise measurement of the magnetic field magnitude. To separately determine the electric fields and the magnetic field gradients, the electron energy is varied betwen 1.0 and 0.5 keV. Time-resolution varies with ambient conditions, but should typically be 100 ms or better. The electron drift instrument on EQUATOR-S is identical to the instrument developed for CLUSTER.

G. Paschmann (MPE Garching, Germany) is the LI.

Routine measurement example (April 28, 1998).

3D-Plasma Analyzer (3DA)

The instrument consists of an electron electrostatic analyzer (EESA) and an ion electrostatic analyzer (PESA). The analyzer is a symmetrical spherical-section electrostatic analyzer (top-hat design) with a disc-shaped field of view (FOV) of 180° directed perpendicular to the spacecraft body. The complete solid-angle sphere is thus covered in one spin period of 1.5 s. The analyzers measure electron and ion distribution functions in 192 angle and 56 energy channels, in the energy-per-charge range 10 eV - 25 keV. Moments of the distributions are computed on board. The 3DA instrument (together with the EPI instrument) is a derivative of the 3D Plasma and Energetic Paricle Instrument on the WIND spacecraft.

G. Parks (U. of Washington, Seattle, USA) is the LI.

Energetic Particle Instrument (EPI)

Physically part of the 3DA instrument, EPI consists of an array of solid-state telescopes measuring electrons and ions in the energy range 20 - 226 keV and 20 - 400 keV, respectively, in 6 energy channels and 4 angle channels at a time. During each spacecraft spin the telescopes trace out a large fraction (70%) of the solid-angle sphere.

T. Sanderson (ESTEC, The Netherlands) is the LI.

First EPI result (December 16, 1997).

Ion Composition Instrument (ICI)

ICI measures the 3D distribution functions of the major ion species, H+, He+, He++, and O+. It consists of a retarding-potential analizer (RPA), followed by a toroidal energy-per-charge (E/q) analyzer with disc-shaped field of view, followed by a 20 kV post-acceleration into a time-of-flight (ToF) analysis section. Without RPA operation, the E/q range is 15 V to 40 kV, otherwise it starts at essentially zero volts. To accommodate the large dynamic range in ion fluxes, the instrument has split the 360° FoV into two 180° sections whose sensitivities differ by a factor 100. Moments of the distributions of all 4 ion species are computed on board and are available every 4 spins, i.e., every 6 s. The instrument is identical to the CODIF portion of the CIS instrument on CLUSTER.

L. Kistler (UNH Durham, USA) is the LI.

First ICI result (January 8, 1998)

Potential Control Device (PCD)

The purpose of the PCD is to reduce the spacecraft potentials to a few volts, levels sufficiently low to allow plasma particle measurements down to very low energies. For this purpose, the PDC emits beams of 6 keV indium ions to compensate the positive charging that would otherwise exist under most circumstances. The emission principle is field evaporation and ionisation of the liquid metal covering a needle by applying a high voltage. Beam currents are variable and can either be set to fixed values, or are adjusted automatically based on the electron energy spectrum measured by the 3DA instrument that is transmitted to PCD in real-time. PCD is identical to the ASPOC instrument dveloped for CLUSTER.

K. Torkar ( IWF Graz, Austria) is the LI.

First PCD result (January 27, 1998)

Scintillating Fiber Detector (SFD)

SFD is based on the light emission property of some materials when hit by ionising radiation. Optical fibers guide the emitted light to a photodiode operated in current mode. A logarithmic amplifier converts this detector current to an analog output voltage. Energy discrimination is achieved by using three differently shielded channels. This way electrons above 0.26, 0.4, and 1.9 MeV are measured, and protons above 6.3, 9.5, and 35 MeV, with a time resolution of 64 s. A constant current is added periodically to calibrate the system.

L. Adams (ESTEC, The Netherlands) is the LI.

Last update of this page 2004-12-13 by Helmut Steinle . Please send comments to !

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