Magnetic moment testing of LISA Pathfinder flight-model units

10 Nov 2009

Illustration of the LISA Technology Package on LISA Pathfinder which carries the two test masses (each a Gold/Platinum alloy cube of 46 mm on a side and weighing almost 2 kg). Credit: ESA

The LISA Pathfinder mission objective is to verify that a test mass onboard the spacecraft can be kept 'free-floating', subject to unwanted accelerations of less than 3×10^-14 m/s². Practically, free-floating means that the 2 test masses inside the spacecraft must not be subject to forces originating from mechanical contact and must only be subject to electrical, magnetic, thermal and internal gravitational forces leading to accelerations of less than 3×10^-14m/s². This in turn leads to stringent requirements on the magnetic characteristics of the spacecraft to prevent spurious magnetic fields affecting the two test masses that form the heart of the mission.

To minimise the magnetic disturbance arising from individual elements careful attention is paid to the selection of materials and tools that are used during the construction process. However, even under the best conditions some residual magnetic field is associated with each unit on the spacecraft.

The purpose of the magnetic moment test programme, which began in June this year and will continue until the end of 2009, is to characterise the magnetic field arising from each unit and to determine that the magnetic cleanliness requirements of the mission will be met.

Some of the LISA Pathfinder flight-model payload units that have been tested in the Magnetic Coil Facility (MCF) at ESTEC.  Clockwise from top left: the Inertial Sensor Front End Electronics Power Converter, Inertial Sensor Sensing and Actuation Unit, Data Management Unit (all pictured in the MCF), laser modulator electronics unit, laser modulator unit, and ultraviolet lamp unit (one element of the charge management device).

The tests are being performed using 'Magnetic Coil Facilities' at ESA's European Space Research and Technology Centre (ESTEC), in Noordwijk, the Netherlands, at EADS Astrium Stevenage, in the UK, and at EADS Astrium Friedrichshafen, in Germany.

Magnetic moment test programme summary
Unit	Provided by	Test site
Laser Modulator Electronics (LME)	RUAG (CH) / APC Université Paris	ESTEC
Laser Modulator Unit (LMU)	Kayser Threde (D) / Max Planck Albert Einstein Institute	ESTEC
Inertial Sensor Front End Electronics (IS FEE)	RUAG (CH) / ETH	ESTEC
Phase Meter Unit (PMU)	University of Birmingham (UK) / STFC	EADS Astrium Stevenage
Charge Management Device (CMD)	Imperial College London (UK) / STFC	ESTEC
Data and Diagnostic Subsystem (DDS)	NTE - SENER (E) / Institut d’Estudis Catalans	ESTEC
Caging Control Unit (CCU)	Thales Alenia Space (I) / ESA	ESTEC
Reference Laser Unit (RLU)	Tesat (D) / Max Planck Albert Einstein Institute	EADS Astrium Friedrichshafen

Upon successful completion of the complete environmental test programme - these magnetic moment tests are amongst the final tests in the programme - the individual units will be delivered to the payload architect, EADS Astrium Friedrichshafen, in order to begin the electrical integration and flat-bed testing campaign.

Contact

Bengt Johlander, LISA Pathfinder Senior Instrument System Engineer
Science and Robotic Exploration Directorate, ESA, The Netherlands.
Email: Bengt.Johlanderesa.int