LISA Pathfinder can measure nanometer motion at a distance of 1.5 million kilometers from Earth
LISA Pathfinder advances on schedule and today we are now a little closer to the key moment of the mission: the release of the test masses in free-fall to test if we can detect gravitational waves. The lock fingers that kept the two test masses on LISA Pathfinder secure during the launch and cruise phase were successfully unlocked. As planned, the two cubes are still attached to the spacecraft via an additional mechanism that will hold them in place until mid-February.

“Until now,” explained the researcher Miquel Nofrarias “Each cube was held in position by eight launch lock fingers pressing the cube’s eight corners. So, this mechanism protected the masses of the forces to which they were subjected during launch”.


Now an additional mechanism called GPRM (Grabbing Position and Release Mechanism) is softly holding the two opposite faces of each cube. This mechanism is also responsible of the test masses release in the vacuum at the right time.

“Motion sensors around the masses are already operational” added Nofrarias “that allows us to measure nanometric movements within the satellite. In this case, however, now we are the responsible of moving the masses inside the aircraft”.

In mid-February, the masses will be released into the aircraft. Before that, all systems and the on-board computer, that will follow the test masses in free fall conditions, will be checked.

Miquel Nofrarias explained that “the release of the masses is a critical moment in the mission. All the previous steps have been tested in the laboratories but we cannot eliminate the gravitational field of the Earth and therefore this is the first time that we will performed this procedure in full”.

The mechanism must release each cube with a positional accuracy of approximately 200 ?m with respect to the geometrical centre in all three directions. To avoid reaching any of the walls, the masses must be released with a velocity of less than 5 ?m/s, or 18 mm/h, meaning that it would take them about a quarter of an hour to cover the space separating them from the surrounding walls.

Once the test masses are released and remain in freefall, scientific tests will begin on March 1st.

More information at the ESA website
Attached Documents
Generalitat de CatalunyaUniversitat de BarcelonaUniversitat Autònoma de BarcelonaUniversitat Politècnica de CatalunyaConsejo Superior de Investigaciones CientíficasCentres de Recerca de Catalunya