Free Astronomy Magazine January-February 2016

ASTRONAUTICS even less than the size of an atom! To record the passage of a gravitational wave it is there- fore necessary to build a sensor capable of detecting move- ments on the scale of billionths of a millimetre. Even Einstein and other eminent scientists of that time were very sceptical about the possibility of discov- ering gravitational waves, due both for the weakness of these S ide video, re- presentation of the complex trajectory fol- lowed by the LISA Pathfinder. Below, an illustra- tion showing the probe’s main com- ponents. [ESA/ ATG medialab] radiations and because any instrument used and the environment surround- ing them could in turn generate a grav- itational field stronger than the sought signal and thus hide it. Since in ground experiments such limi- tations have proved harmful, already a couple of decades ago researchers had begun to design experiments to be con- ducted in space. The aim was to observe the behaviour of “test masses” float- ing freely in the cosmic void. The most difficult task from the engineering standpoint was precisely to ensure that on such test masses there weren’t any forces acting outside the gravitational one. Clearly, the probe laboratory in- tended to contain the experiment had to be made so as to not generate any “gravitational noise"; in short, it was essential that its mass was uniformly distributed around the test masses with such precision that even the dis- placement of a thin copper wire would upset the equilibrium. Back in the ‘90s, NASA and ESA decid- ed to cooperate in developing a fore- runner mission capable of testing the technologies needed for detecting gravitational waves, and in 2000, the ESA's Science Programme Committee approved the design of the LISA Path- finder mission (where LISA stands for Laser Interferometer Space Antenna), whose launch was scheduled for 2008, as part of the ESA’s SMART program (Small Missions for Advanced Research