Each cube is 1.96 kg of polished perfection, a 46-mm-sided regular hexahedron of gold-platinum alloy. This material is used because it has a low magnetic susceptibility, not just to make a prize higher than Olympic gold for shot put far above and beyond the call of gravity.
The cubes will float inside LISA-P. Lasers will track how far it is from them to within a billionth of a meter, firing liquid metal ion thrusters to maintain the correct distance. This will be the Solar System's only smart game of "not touching you, can't get mad or inaccurate." Laser interferometry will also track the distance between the cubes down to the picometer. Flying through the heavens while measuring things accurate to trillionths of a meter. If angels did dance on the head of a pin, this system could read their shoe size.
ESA, Albert Einstein Institute
This is just the housing for the cubes, and it makes a wedding ring box look like a greasy taco wrapper.
The cubes will fly in almost perfect free fall, protected from everything else in existence, their motion tracing geodesics across the surface of spacetime. We're throwing stones not to see the splash but to surf the shape of reality itself. So LISA will go up high, find something precious inside itself, create an inner calm so that nothing can disturb it, feel the harmonics of light bouncing back and forth between the shining centers, and use this inner harmony to map the shape of the universe. This is a Zen spacecraft.