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The accurate measurement of the magnetic field along the orbits of the four Cluster spacecraft is a primary objective of the mission. The magnetic field is a key constituent of the plasma in and around the magnetosphere, and it plays an active role in all physical processes that define the structure and dynamics of magnetospheric phenomena on all scales. With the four-point measurements on Cluster, it has become possible to study the three-dimensional aspects of space plasma phenomena on scales commeasurable with the size of the spacecraft constellation, and to distinguish temporal and spatial dependences of small-scale processes. We present an overview of the instrumentation used to measure the magnetic field on the four Cluster spacecraft and an overview the performance of the operational modes used in flight. We also report on the results of the preliminary in-orbit calibration of the magnetometers; these results show that all components of the magnetic field are measured with an accuracy approaching 0.1 nT. Further data analysis is expected to bring an even more accurate determination of the calibration parameters. Several examples of the capabilities of the investigation are presented from the commissioning phase of the mission, and from the different regions visited by the spacecraft to date: the tail current sheet, the dusk side magnetopause and magnetosheath, the bow shock and the cusp. We also describe the data processing flow and the implementation of data distribution to other Cluster investigations and to the scientific community in general.Key words. Interplanetary physics (instruments and techniques) – magnetospheric physics (magnetospheric configuration and dynamics) – space plasma physics (shock waves)

The properties of low frequency magnetotail waves observed during CASSINI’s Earth swing-by are examined. A maximum in the distribution of the waves about half the proton cyclotron frequency and a peak at linear polarisation are found and their implications are analysed in detail. Data on the fluid plasma velocity for the observation interval are not available and thus no unique conclusions about Doppler shift influence on the properties of the waves can be made. This determines the need to analyse different hypotheses in order to understand the origin of the waves. The plausibility of competing interpretations, such as off-resonance proton cyclotron waves and bi-ion cyclotron waves at the gyrofrequency of a heavy ion component of the magneto-tail plasma in the form of He ++ ions of solar wind origin is questioned.Key words. Space plasma physics (waves and instabilities) – Magnetospheric physics (plasma waves and instabilities; magnetotail)

Deep Space 1 (DS1) is the first interplanetary spacecraft (s/c) using ion propulsion and aims at investigating the compatibility of innovative technology with scientific measurements. DS1 performed a successful flyby at the asteroid Braille on July 29th, 1999. This closest-ever encounter allowed for the first time a direct measurement of an asteroidal magnetic field. The manifold magnetic disturbances caused by the ion propulsion onboard DS1, however, required an elaborate data processing scheme in order to extract the magnetic signature of Braille. Its successful application to the magnetometer data of the asteroid flyby reveals a magnetic moment of 2.1 · 1011Am² for Braille.

Planet Mars is currently an object of increasing scientific and public interest. Several spacecraft are on their way or planned to be sent to our neighbour planet to unravel its secrets. One of the most unknown properties of planet Mars is whether it possesses a planetary magnetic field of dynamo origin. Observed weak surface magnetic fields seem to argue against a currently operating planetary dynamo. However, weak surface fields are also expected if a polarity reversal occurs. We shall discuss arguments in favour and against the speculation that Mars still operates an active dynamo with the weak surface magnetic fields pointing towards an ongoing reversal. As the possible way to validate this speculation we discuss the importance of a spherical harmonic expansion of the Martian magnetic field. The planned NetLander project and its anticipated magnetic field measurements are a powerful tool to provide at least a low-order spherical harmonic expansion coefficient determination of the Martian magnetic field, thereby allowing to study characteristics of crustal magnetic field anomalies as well as giving clues to the question whether Mars is a planet in magnetic transition.

In this paper we present the measurements and interpretations of the Tethered Magnetometer (TEMAG) experiment flown on the Tethered Satellite Mission Reflight TSS-IR. Data were taken during the active operating phase when current steps of variable amplitude were injected along the electrically conducting tether. The magnetic field shows clear signatures in the components and amplitude, dependent upon the orientation of the magnetometer boom with respect to the spacecraft ram velocity vector. In the eight events studied, current effects could be observed in the magnetic field data only when the boom was pointing toward the ram side hemisphere of the satellite. The picture emerging from the observed results suggests the formation of a current sheet on the ram side, possibly associated with the aerodynamic shock and compression of the geomagnetic field ahead of the satellite. Although the limited data do not allow full description of the phenomenology, they place important observational constraints on any theoretical model.

International audience; The NetLander Mission will deploy four landers to the Martian surface. Each lander includes a network science payload with instrumentation for studying the interior of Mars, the atmosphere and the subsurface, as well as the ionospheric structure and geodesy. The NetLander Mission is the first planetary mission focusing on investigations of the interior of the planet and the large-scale circulation of the atmosphere. A broad consortium of national space agencies and research laboratories will implement the mission. It is managed by CNES (the French Space Agency), with other major players being FMI (the Finnish Meteorological Institute), DLR (the German Space Agency), and other research institutes. According to current plans, the NetLander Mission will be launched in 2005 by means of an Ariane V launch, together with the Mars Sample Return mission. The landers will be separated from the spacecraft and targeted to their locations on the Martian surface several days prior to the spacecraft's arrival at Mars. The landing system employs parachutes and airbags. During the baseline mission of one Martian year, the network payloads will conduct simultaneous seismological, atmospheric, magnetic, ionospheric, geodetic measurements and ground penetrating radar mapping supported by panoramic images. The payloads also include entry phase measurements of the atmospheric vertical structure. The scientific data could be combined with simultaneous observations of the atmosphere and surface of Mars by the Mars Express Orbiter that is expected to be functional during the NetLander Mission's operational phase. Communication between the landers and the Earth would take place via a data relay onboard the Mars Express Orbiter.

The Rosetta spacecraft will rendez-vous with comet Wirtanen round 2011 and will study it for a period of nearly two years, thus providing a unique opportunity to monitor its behaviour over a wide range of distances from the Sun. A plasma and wave package, the Rosetta Plasma Consortium, RPC, will be part of the Rosetta orbiter payload. RPC is a highly integrated package that consists of five sensors: the Langmuir Probe, LAP, the Ion and Electron Sensor, IES, the Ion Composition Analyzer, ICA, the Fluxgate Magnetometer, MAG, and the Mutual Impedance Probe, MIP. RPC also includes the common instrument control, spacecraft interface, and power management unit, PIU, plus the Electrical Ground Support Equipment, EGSE. The prime objectives of RPC are to investigate: (1) the physical properties of the cometary nucleus and its surface, (2) the inner coma structure, dynamics, and aeronomy, (3) the development of cometary activity, and the microscopic and macroscopic structure of the solar-wind interaction region as well as the formation and development of the cometary tail. In addition, the planned asteroid, possibly Otawara and Siwa, flybys will provide an excellent opportunity to study in detail the physics of the solar wind-asteroid interaction. The magnetic and electric conductivity properties of the asteroid will also be studied.

A mission to Mars including two Small Stations, two Penetrators and an Orbiter was launched at Baikonur, Kazakhstan, on 16 November 1996. This was called the Mars-96 mission. The Small Stations were expected to land in September 1997 (Ls approximately 178 degrees), nominally to Amazonis-Arcadia region on locations (33 N, 169.4 W) and (37.6 N, 161.9 W). The fourth stage of the Mars-96 launcher malfunctioned and hence the mission was lost. However, the state of the art concept of the Small Station can be applied to future Martian lander missions. Also, from the manufacturing and performance point of view, the Mars-96 Small Station could be built as such at low cost, and be fairly easily accommodated on almost any forthcoming Martian mission. This is primarily due to the very simple interface between the Small Station and the spacecraft. The Small Station is a sophisticated piece of equipment. With the total available power of approximately 400 mW the Station successfully supports an ambitious scientific program. The Station accommodates a panoramic camera, an alpha-proton-x-ray spectrometer, a seismometer, a magnetometer, an oxidant instrument, equipment for meteorological observations, and sensors for atmospheric measurement during the descent phase, including images taken by a descent phase camera. The total mass of the Small Station with payload on the Martian surface, including the airbags, is only 32 kg. Lander observations on the surface of Mars combined with data from Orbiter instruments will shed light on the contemporary Mars and its evolution. As in the Mars-96 mission, specific science goals could be exploration of the interior and surface of Mars, investigation of the structure and dynamics of the atmosphere, the role of water and other materials containing volatiles and in situ studies of the atmospheric boundary layer processes. To achieve the scientific goals of the mission the lander should carry a versatile set of instruments. The Small Station accommodates devices for atmospheric measurements, geophysical and geochemical studies of the Martian surface and interior, and cameras for descent phase and panoramic views. These instruments would be able to contribute remarkably to the process of solving some of the scientific puzzles of Mars.

The paper presented is a comprehensive description of the MARS-96 SAS (small autonomous station) magnetometer experiment. Starting with a detailed discussion of what is known about the magnetic field on and around Mars as well as the Moon and Earth in comparison, the scientific objectives clearly lead to the design goals for a magnetic field instrument to be part of the scientific payload of a Mars lander. The magnetometer is presented in general and partly in more detail e.g. how to achieve a fairly good temperature stability over the expected temperature range of −80°C–+40°C, or with respect to the design of the attitude determination devices. In a final part, a discussion of the magnetic cleanliness of spacecrafts (S/C) in general, and the SAS in detail, is given. As a result it is shown, that despite the reduced Mars-96 magnetic cleanliness programme as for the SASs only, a distortion field of less than 10 nT at the magnetometer's sensor position was achieved. This gives strong confidence for the magnetic field measurements.

During the TSS-1R flight, conditions occurred under which very intense currents flowed through the tether wire system. The effect of these currents during the active phases of operation was clearly seen by the TEMAG sensor assembly located on the short, fixed satellite boom. Magnetic signatures appeared on the field components parallel to the boom and to the spin axis with a strong peak when the boom points closer to the ram direction. While a toroidal current flowing on the ram side of the plasma sheath may explain the main features seen by the TEMAG outboard sensor, further studies are needed for the physical interpretation of the complex electrodynamic interactions of the TSS-ionosphere system.

The transient variations of the magnetic field at the surface of a planet has a primary external source, the interaction between the environment of the planet and solar radiation, and a secondary source, the electric currents induced in the conductive planet. The continuous recording of the time variations of the magnetic fields at the surface of Mars by means of three component magnetometers installed onboard landers would therefor allow the study of both the internal structure of Mars and the dynamic of its ionized environment.

Zero-level determination is an important aspect of the processing of magnetometer observations made onboard spacecrafts. Due to the presence of instrument offset drift as well as magnetic fields produced by the spacecraft, such a zero-level determination requires in-flight methods in addition to preflight calibration. Two different such techniques have been studied, taking advantage of observations made by instruments other than the magnetometer. The first is based on measurements obtained by electron drift instruments, originally designed to measure electric fields. The authors discuss the applicability of such instruments to determine magnetometer offsets. The second method is based on particle pressure tensor measurements, where pressure anisotropy is used to determine the magnetic field direction.

The Giotto spacecraft was reactivated in February 1990 and performed the first-ever earth gravity-assisted maneuver on July 2, 1990 to be retargeted for Comet P/Grigg-Skjellerup. This swing-by is of unique scientific interest due to Giotto's hyperbolic, high-inclination orbit. This paper reports on scientific results of the Giotto magnetic field experiment. Due to the high fly-by velocity and the relative quietness of the magnetosphere during the swing-by period, these measurements present a snapshot view of the earth magnetosphere with clearly identified inbound and outbound bow shock and magnetopause crossings. The outbound crossings are of particular interest as surface waves at the polar magnetopause at a distance of 28 earth radii as well as a strong quasi-perpendicular bow shock at a distance of about 64 earth radii are observed.

The authors report thirteen very short events in the magnetic field of the inner magnetic pile-up region of comet Halley observed by the Giotto magnetometer experiment together with simultaneous plasma data obtained by the Johnstone plasma analyzer and the ion mass spectrometer experiments. The events are due to dust impacts in the milligram range on the spacecraft at the relative velocity between the cometary dust and the spacecraft of 68 km/sec. They are generally consistent with dust impact events derived from spacecraft attitude perturbations by the Giotto camera (Curdt and Keller, private communication). Their characteristic shape generally involves a sudden decrease in magnetic field magnitude, a subsequent overshoot beyond initial field values and an asymptotic approach to the initial field somewhat reminiscent of the magnetic field signature after the AMPTE releases in the solar wind. These observations give a new way of analyzing ultra-fast dust particles incident on a spacecraft.

International audience; The Rosetta Plasma Consortium (RPC) will make in-situ measurements of the plasma enviromnent of comet 67P/Churyumov-Gerasimenko. The consortium will provide the complementary data sets necessary for an understanding of the plasma processes in the inner coma, and the structure and evolution of the coma with the increasing cometary activity. Five sensors have been selected to achieve this: the Ion and Electron Sensor (IES), the Ion Composition Analyser (ICA), the Langmuir Probe (LAP), the Mutual Impedance Probe (MIP) and the Magnetometer (MAG). The sensors interface to the spacecraft through the Plasma Interface Unit (PIU). The consortium approach allows for scientific, technical and operational coordination, and makes Optimum use of the available mass and power resources.

The fluxgate magnetometer experiment onboard the ROSETTA spacecraft aims to measure the magnetic field in the interaction region of the solar wind plasma with comet 67P/Churyumov-Gerasimenko. It consists of a system of two ultra light (about 28 g each ) triaxial fluxgate magnetometer sensors, mounted on the 1.5 m long spacecraft boom. The measurement range of each sensor is ±16384 nT with quantization steps of 31 pT. The magnetometer sensors are operated with a time resolution of up to 0.05 s, corresponding to a bandwidth of 0–10 Hz. This performance of the RPC-MAG sensors allows detailed analyses of magnetic field variations in the cometary environment. RPC-MAG furthermore is designed to study possible remnant magnetic fields of the nucleus, measurements which will be done in close cooperation with the ROSETTA lander magnetometer experiment ROMAP.

[1] The NASA DS1 spacecraft flew past comet P/Borrelly on September 22, 2001, on the sunward side of the comet. Dust impacts were detected by sharp increases (or decreases) in electric fields measured by the plasma wave dipole antennae. Electric pulses from as small as 0.014 Vm−1 to saturation (∼±0.8 Vm−1) were detected. Pulse overshoots were noted in the largest electric pulses. No simultaneous dc magnetic signatures >1 nT were detected in the magnetometer data. Assuming that cometary dust grains propagating in the sunward direction were decelerated by solar radiation pressure, arguments are made that the size of the earliest dust particles detected were probably ∼0.4 μm in radius. Elaboration of the characteristics of these electric pulses and pulse overshoots and their interpretations will be reserved for a subsequent work.

The Deep Space One mission is demonstrating the long-duration use of an Ion Propulsion Subsystem (IPS). The NASA Solar Electric Propulsion Technology Applications Readiness Project developed the NSTAR Diagnostics Package (NDP) to monitor the effects of the IPS on the spacecraft environment. The NDP measures contamination, plasma characteristics, electric fields, and magnetic fields. This paper describes the NDP requirements, development process, and flight systems' functionality. NDP functionality exceeded expectations; it became an effective tool in the detection and diagnosis of spacecraft functionality and system anomalies. NDP detects hydrazine thruster firings (planned and not planned), ion engine gimbal stepper motor currents, solar array currents, spacecraft charging, as well as a number of other phenomena. Examples of selected ion engine and spacecraft signatures and their interpretations are discussed.

International audience; In the frame of the international cooperation for Mars exploration, a set of 4 NetLanders developed by an European consortium is expected to land on the planet during the forthcoming years. Among other instruments, the geophysical package of each lander will include a magnetometer. The different possible contributions of magnetic measurements onboard the NetLander stations are presented. Intrinsic planetary field and remanent magnetisation investigations by means of magnetometers onboard a network of landers are first considered, and the information that can be thus derived on the Martian core dynamo and surface rocks, soil, and dust is discussed. The contribution of permanent recording of the magnetic transient variations at a network of surface stations is then discussed. The transient variations of the magnetic field at the surface of a planet has a primary external source, the interaction between the environment of the planet and solar radiation, and a secondary source, the electric currents induced in the conductive planet. The continuous recording of the time variations of the magnetic field at the surface of Mars by means of three component magnetometers installed onboard NetLander stations will therefore allow study of both the internal structure of Mars and dynamics of its ionised environment. The expected characteristics of transient magnetic variations, and their relation with plasma flow and current in the Mars ionised environment are discussed. The use of the network magnetic data to probe the internal structure of Mars is also considered. The used techniques are presented, and the information that can be thus obtained on the Mars permafrost, lithosphere and mantle structure illustrated by numerical simulations. Finally, the specifications of the instrument allowing to achieve these objectives are discussed, and the instrument described.

The Cluster mission provides a new opportunity to study plasma processes and structures in the near-Earth plasma environment. Four-point measurements of the magnetic field will enable the analysis of the three dimensional structure and dynamics of a range of phenomena which shape the macroscopic properties of the magnetosphere. Difference measurements of the magnetic field data will be combined to derive a range of parameters, such as the current density vector, wave vectors, and discontinuity normals and curvatures, using classical time series analysis techniques iteratively with physical models and simulation of the phenomena encountered along the Cluster orbit. The control and understanding of error sources which affect the four-point measurements are integral parts of the analysis techniques to be used. The flight instrumentation consists of two, tri-axial fluxgate magnetometers and an on-board data-processing unit on each spacecraft, built using a highly fault-tolerant architecture. High vector sample rates (up to 67 vectors s-1) at high resolution (up to 8 pT) are combined with on-board event detection software and a burst memory to capture the signature of a range of dynamic phenomena. Data-processing plans are designed to ensure rapid dissemination of magnetic-field data to underpin the collaborative analysis of magnetospheric phenomena encountered by Cluster.

This paper describes the magnetometer instrument (MAG) to be flown on the Cassini spacecraft. The instrument consists of two magnetometers and an on-board data processing unit. One magnetometer is a Vector Helium device of a type previously flown on Ulysses and several other missions which has been modified to operate in a Scalar mode providing measurements of the magnitude of the local magnetic field with very small absolute error. This is the first flight of such an instrument. The other magnetometer is a Fluxgate device of similar design to that flown on Ulysses and on many previous missions but with newly developed electronics. Both magnetometers can provide vector measurements of the three components of the magnetic field with a sensitivity of about 10pT. The unique combination of Fluxgate/Scalar or Fluxgate/Vector Helium operation offers increased possibilities for scientific investigation of the magnetic field environment in the Saturnian system. The data processing unit contains dual redundant systems based on the 80C86 microprocessor. It features sophisticated on-board data processing, large internal data storage capability and internal failure detection and recovery, giving the instrument the capability to operate autonomously for extended periods. The MAG instrument development team is drawn from institutes in four countries reflecting the multi-national flavor of the Cassini/Huygens mission.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Helios search coil experiment provides accurate low background noise measurements of interplanetary magnetic fluctuation spectra from about 4 Hz to 2.2 kHz adjacent to the frequency band from 0 to 4 Hz of the Technical University of Braunschweig flux-gate magnetometer. Apart from a slowly varying fluctuation component ranging up to 100 Hz near 1 AU and beyond 500 Hz near 0.3 AU the following superposed ‘events’ can be discerned in the fluctuation spectra which also have a distinct signature in the slowly varying magnetic field: (1) directional discontinuities acting as wave guide boundaries, (2) directional discontinuities producing whistler wave fields because of instability, (3) reversible magnetic field variations, mostly dips of about 1 min duration associated with whistler wave fields, (4) interplanetary shocks, where, for example, the oblique shock of January 8, 1975, has a thickness of about 1 proton gyroradius and produces an increase in whistler wave fields by more than 2 orders o′ magnitude in power spectral density leading to a power spectrum of 1 γ²/Hz f−3.64 in the wake region.

On Milos island, the Institute for Geophysics, Technical University of Braunschweig, performed measurements with Active Audiomagnetotellurics (AAMT) at 41 sites and with passive magnetotellurics at 3 sites. The frequency range covered is 0.05 Hz to 2500 Hz. Comparison with well logs shows that it is possible to assign an increase of resistivity at depths of 200 – 500M to the top of the crystalline basement at many sites. This surface is compared with the gravity measurement for a profile across the Zephyria Graben. AAMT far-field data and long period MT data fit well and can be used for a common interpretation with a frequency range of more than six decades.

One of the most important goals of the HELIOS-1 and -2 missions is the investigation of discontinuities with strong variations in the magnetic-field magnitude as, for example, shock waves. Observational studies of such events with high time resolution at low telemetry rates require an on-board automatic identification system and a big core memory. For this purpose a quality index is calculated on board using both a long and short time average of the magnetic-field data. By this quality index the memory read in is triggered. The principle of operation and the technical layout is discussed.

The Giotto magnetometer experiment employs a low-mass (1.357 kg), low-power (818 mW) instrument in a dual magnetometer configuration using flux gate sensors of the ring core type. It has provided accurate vector magnetic field measurements on its way to and near Comet Halley, working flawlessly from switch-on on 22 August 1985 to the formal end of the mission on 15 March 1986.

In October 1981 the AAMT method was tested in the geothermal field of Travale. This method is based on the MT method, but uses artificial EM fields excited by a transmitter some kilometres from the receiving station. The transmitter consists of a switch mode amplifier for the lower frequency band (

The Giotto magnetometer experiment at comet Halley has for the first time provided magnetic field measurements in all the important spatial regions characterizing the front-side interaction between the solar-wind magnetoplasma and a cometary atmosphere. Upstream waves of cometary origin have been observed at distances greater than two million km from the comet, both inbound and outbound. A cometary bow shock has been identified at 1.15 million inbound on the dawn side and a thick quasi-parallel cometary bow shock outbound. A turbulent magnetosheath has been observed further inside. A magnetic pile-up region has been identified inside 135,000 km, inbound, and 263,000 km, outbound, with fields up to 57 and 65 nT, respectively. A cavity region with essentially zero magnetic field has been discovered, with a width of 8500 km along the trajectory around closest approach.

A digital coding scheme for colour television signals is presented that uses a transmission rate of 34 Mbit/s and does not show any picture quality degradations when compared with pictures of the 625-line PAL standard. The luminance and chrominance signals are coded separately by extended differential pulse-code modulation (DPCM). For the example of the luminance decoder an implementation in ECL gate array technology is described.

It was the aim of this investigation to develop and test a probe for in-situ thermal conductivity measurements also applicable for rocks. First a new theory for a spherical probe for absolute measurements was developed. A sensor including the spherical probe (heater) and a downhole hydraulic drilling mechanism for drilling well defined special side boreholes was constructed and tested in limestone clay and slate. A first application of the sensor was done in flat drillings around Lake

In 1978 and 1979 a total of 9 geoelectric Schlumberger soundings and 14 magnetotelluric soundings were carried out along a 10 km profile across Lake Laach in the Eifel volcanic area.

The existence of hydromagnetic waves in the mass-loaded solar wind upstream from the bow shock of a comet is well-established both for comet Giacobini-Zinner and for comet Halley. Whereas previous reports have been concerned either with the magnetic field observations or with plasma observations, here we combine observations of the magnetic field with the solar wind proton and alpha particle distributions. This allows the three possible modes of propagation for these waves to be separated. The magnetic component is predominantly transverse to the magnetic field and linearly polarised. The flow vector also has a substantial amount of power parallel to the magnetic field. A examination of the pressure variations shows that slow magnetosonic waves are more common than the fast mode.