The payload of SWARM satellites is mainly composed of instruments measuring the magnetic field and satellite positionning and orientation instruments. The vector measurement of the magnetic field is ensured by a fluxgate magnetometer (VFM) but this measurement is not absolute (drift, offset). A second instrument (ASM) intended for the absolute and scalar measurement of the magnetic field is then necessary to calibrate the fluxgate.

ASM instrument developed by Leti and provided by the CNES to SWARM is a magnetometer with optical pumping which uses the Zeeman effect on Helium 4 atoms and which proved suitable for terrestrial applications (in particular for the DGA). This instrument operation is different from the Ørsted and Champ missions instruments (magnetometers with precession of protons) and is in fact a more accurate instrument. Moreover, thanks to a cofinanced thesis CNES/CEA, Leti showed the possibility of carrying out absolute and vector measurements (3D) with the same instrument at the same point in space at the same Time. This required two separate instruments so far. It is planned to operate the vector mode in a demonstration mode in order to validate in space this new instrumental concept which should open interesting possibilities for future space missions measuring the Earth or planetary magnetic fields.

Picture of the ASM sensors in their mount as well as the Digital Processing Unit (DPU) © LETI

More detailed information on this instrument are available in the following links:

ASM Instrument Description and Architecture
ASM Instrument Performances

The avalaible publications are as follow:

1st SWARM international science meeting that took place from May 3 to 5, 2006 at Nantes, France: abstract and poster
2nd SWARM international science meeting that took place from June 24 to 26, 2009 in Potsdam: LETI - CNES publication
Eurosensors XXIII that took place from September 6 to 9, 2009 in Lausane: LETI - CNES publication