Scientific instruments for challenging and cost-optimized space missions have to reduce their resource requirements while keeping the high performance levels of conventional instruments. In this context the development of an instrument front-end ASIC (0.35 mu m CMOS from austriamicrosystems) for magnetic field sensors based on the fluxgate principle was undertaken. It is based on the combination of the conventional readout electronics of a fluxgate magnetometer with the control loop of a sigma-delta modulator for a direct digitization of the magnetic field. The analogue part is based on a modified 2-2 cascaded sigma-delta modulator. The digital part includes a primary (128 Hz output) and secondary decimation filter (2, 4, 8,..., 64 Hz output) as well as a serial synchronous interface. The chip area is 20 mm(2) and the total power consumption is 60 mW. It has been demonstrated that the overall functionality and performance of the magnetometer front-end ASIC (MFA) is sufficient for scientific applications in space. Noise performance (SNR of 89 dB with a bandwidth of 30 Hz) and offset stability (< 5 pT degrees C-1 MFA temperature, < +/- 0.2 nT within 250 h) are very satisfying and the linear gain drift of 60 ppm degrees C-1 is acceptable. Only a cross-tone phenomenon must be avoided in future designs even though it is possible to mitigate the effect to a level that is tolerable. The MFA stays within its parameters up to 170 krad of total ionizing dose and it keeps full functionality up to more than 300 krad. The threshold for latch-ups is 14 MeV cm(2) mg(-1).

This paper describes the concept and development of an innovative combination of conventional fluxgate magnetometer readout electronics with the control loop of a sigma-delta modulator in order to achieve a new magnetometer design that provides direct digital output without the use of a separate analogue-to-digital converter chip. The new concept is especially aimed at the measurement of extraterrestrial magnetic fields within a dynamic range of approximately +/-2000 nT aboard scientific space missions which are affected by high radiation doses.A digital domain model of the new magnetometer electronics is presented, which is essential for a successful hardware implementation, and the test results of a single-axis prototype are discussed.The test results show that the fluxgate and sigma-delta modulator control loops can be merged for dynamic ranges up to +/-2000 nT without significant deterioration of the overall performance of the magnetometer. The remaining quantization noise in the signal bandwidth (10 Hz) was minimized to below the sensor's noise level (7 PT Hz(-1/2) at 1 Hz) due to the noise-shaping effect of the sigma-delta principle. An offset stability of 0.25 nT over four days was achieved and the linearity error is less than +/-3.3 x 10(-5) even though the fluxgate sensor is not kept at near-zero field as for traditional fluxgate magnetometers.A technological model of this new fluxgate magnetometer concept will be built for a test flight aboard the NASA discovery mission DAWN.

MERIDIAN is a 120° east ground based multi-station and multi-instrument project proposed in China. IWF/ÖAW in Graz, Austria in cooperation with IGPP/UCLA in Los Angeles, USA and CSSAR/CAS in Beijing, China has developed variometers for magnetic field observations along this MERIDIAN chain. The variometer (CHIMAG) is a fluxgate magnetometer especially for Earth field variation and pulsation measurements. Three variometer stations have been installed in Beijing (40° N), Hainan (19° N) and Wuhan (30.5° N), respectively. Two more will be installed in 1999. In this paper we will present the design and the scientific objectives of the CHIMAG as well as the results of the first observations.

The Space Research Institute of the Austrian Academy of Sciences took part in the experiment MAREMF (MARtian Electrons and Magnetic Field) which consists of a dual fluxgate magnetometer (MAREMF-OS and MAREMF-IS) and a 3D electron spectrometer (MAREMF-ES). MAREMF was part of the plasma payload of the Russian MARS-96 mission which unfortunately failed half an hour after launch because of a rocket problem. Digital electronics and firmware of the MAREMF-OS magnetometer were developed at the Space Research Institute, Graz, Austria. The sensor was supplied by the Institute of Geophysics and Planetary Physics (IGPP), UCLA, USA. The sensor electronics were jointly developed with the IGPP. Due to the expected temperature conditions during cruise phase and the orbit around Mars, an improved low-field temperature test facility for magnetic field sensors was constructed at the Magnetometer Laboratory of the Space Research Institute. It enabled all basic test and calibration measurements for magnetic field sensors within a temperature range of C. Additionally, a three-layer magnetic shielding set generated a low-field environment. The same facility is now used for the development and calibration of a new generation of magnetic field sensors for the ROSETTA mission to comet P/Wirtanen.

The Space Research Institute of the Austrian Academy, of Sciences (Graz, Austria) in cooperation with MPE (Berlin, Germany), GFZ Potsdam (Obs. Niemegk, Germany) IZMIRAN/IOFAN (Moscow, Russian) and IGPP/UCLA (Los Angeles, USA) is designing the magnetic field experiment MAGIBAL (MAGnetic field experiment aboard a martian BALloon) to investigate the magnetic field on the surface of Mars. The dual sensor fluxgate magnetometer is part of the MARS-98/ MARS-TOGETHER balloon payload. During a ten days period the balloon will float over a distance of about 2000 km at altitudes between 0 and 4 km. Due to the limited power and telemetry allocation the magnetometer can transmit only one vector per ten seconds and spectral information in the frequency range from 2 - 25 Hz. The dynamic range is +/- 2000 nT.The main scientific objectives of the experiment are:Determination of the magnetism of the Martian rocksInvestigation of the leakage of the solar wind induced magnetosphere using the correlation between orbiter and balloon observationsMeasurement of the magnetic field profile between the orbiter and the surface of Mars during the descent phase of the balloon.Terrestrial test flights with a hot air balloon were performed in order to test the original MAGIBAL equipment under balloon flight conditions.

The magnetometer on the POLAR Spacecraft is a high precision instrument designed to measure the magnetic fields at both high and low altitudes in the polar magnetosphere in 3 ranges of 700, 5700, and 47000 nT. This instrument will be used to investigate the behavior of fieldaligned current systems and the role they play in the acceleration of particles, and it will be used to study the dynamic fields in the polar cusp, magnetosphere, and magnetosheath. It will measure the coupling between the shocked magnetosheath plasma and the near polar cusp magnetosphere where much of the solar wind magnetosphere coupling is thought to take place. Moreover, it will provide measurements critical to the interpretation of data from other instruments. The instrument design has been influenced by the needs of the other investigations for immediately useable magnetic field data and high rate (100+vectors s−1) data distributed on the spacecraft. Data to the ground includes measurements at 10 vectors per second over the entire orbit plus snapshots of 100 vectors per second data. The design provides a fully redundant instrument with enhanced measurement capabilities that can be used when available spacecraft power permits.