ESA Contract

Bartington takes part in the LISA project

Accurate measurements of magnetic field gradient is critical to many applications. LISA (Laser Interferometer Space Antenna) constitute a prominent example of spacecraft that demands very tight monitoring and control of the magnetic environment (more information can be found about LISA at http://www.esa.int/science/lisa).

The sensitivity goal for the LISA project requires that the test masses (TM – nominally 2kg) are kept in free fall with an acceleration noise limit in the order of 3.10-15m/s2/√Hz at 0.1mHz (s. Vitale & K. Danzmann, “Science Requirements and Top-level Architecture Definition for the Lisa Technology Package (LTP) on Board LISA Pathfinder”, LTPA-UTN-ScRD-Iss003-Rev1, 30 June 2005 http://www.lisa.aei-hannover.de/?page=search⊂=docs&type=all〈=en).

In order to achieve this high purity of geodesic motion, noisy environmental forces are screened by shielding the test masses in a drag-free satellite. Additionally, precision thrusters driven by a position sensor minimize the relative displacement between the satellite and test masses. Among the residual disturbance sources, magnetic effects play an important role. Fluctuations of magnetic fields and the magnetic field gradient will affect the test mass remanent dipole moment and its magnetic susceptibility to produce force noise (J. Hanson et al., “ST-7 gravitational reference sensor: analysis of magnetic noise sources”, Class. Quantum Grav. 20 (2003) S109-S116 http://stacks.iop.org/cp/20/S109).

Due to the need to measure the magnetic field gradient and, more important, its fluctuations down to sub-mHz frequencies, inside enclosures where little room is available and to the highly non-dipolar nature of the field (the inertial sensors are at the centre of the spacecraft, so close to the spurious magnetic field sources), compact gradiometers having a baseline of a few centimetres are desirable.

Magnetic gradiometers featuring low volume, low mass and low power consumption could also be ideally used as diagnostics payloads, as:
  • they can measure and distinguish the fluctuations of field gradients that are due to sources onboard the spacecraft from the fluctuations caused by the interplanetary field;
  • used in sufficient number, they allow a good field reconstruction at TM positions thereby enabling a calculation of magnetic force noise.

Compact and sensitive gradiometers are also valuable for missions requiring magnetic cleanliness, or as testing and investigation tools, or to complement or replace dedicated test facilities.

Bartington Instruments with NPL (National Physical Laboratory) and RAL (Rutherford Appleton Laboratory) have been chosen by ESA to:

  1. Identify the best magnetometer technologies (physical principles, noise reductions techniques, etc.) to meet the requirements of a Compact Low Noise Gradiometer (CLNG), which could be used as a measurement took on the ground or a s diagnostics payload monitoring magnetic cleanliness during space missions;
  2. Selecting the type of sensor, front-end electronics features and gradiometer topology for a suitable CLNG;
  3. Design, manufacture, calibrate and test the CLNG;
  4. Define the architecture of a Magnetic Diagnostics Spacecraft Payload to determine the magnetic field and its gradient (and their time variations) at a given location inside the Spacecraft.

This project started the 15th of October 2009 and is due to finish in November 2011.

 

 

 

 

 

 


Bartington Instruments R&D Department

 

 

 

 


LISA Project