19 Dec 2008 16:21

The vibration tests were set out to verify the science module's compliance with specified requirements, and to assure that the module is able to withstand the conditions that will be encountered during the launch phase of the mission, as well as handling and transportation loads. The technique of "sine burst" vibration excitation has been used for this purpose.

The sine burst is a short sinusoidal vibration which quickly ramps in amplitude to an established level, remains on the highest levels for a very short time and then quickly ramps down. 25 cycles of the sinusoidal waves were applied for the ramps, and only 5 for the highest level, with a frequency of 25 Hz used throughout the test.

For the earlier separation shock tests, performed at the end of October 2008, the STM science module had been mated with the proto flight model (PFM) of the propulsion module and the Launch Vehicle Adapter (LVA). For the recent vibration tests the two spacecraft modules were separated again on 3 November.

These tests have been successfully performed on the ESTEC new 640kN Quad shaker for the longitudinal axis and on the 320kN Multi shaker (MSH) for the lateral axes. The test campaign lasted from the middle of November until the middle of December.

Figure 1 & 2: The LISA Pathfinder science module ready for tests on the vibration test facility in the ESTEC test centre. Credit: ESA

Arrival of flight model science module

On 9 December the flight model (FM) of the science module arrived at ESTEC in its transport and storage container. After careful unloading from the container the FM science module was transferred into the cleanroom for storage.

While the STM test campaign was used to qualify the structural design for static acceleration, the FM science module will under go a workmanship verification in January and February 2009.