In the paper we discuss the composition of a piece for prepared piano, Periplo del latte, that takes into account as its starting point the simulated gravitational wave data for the future LISA space mission. First, we introduce the LISA project and its output. Then, we present Einstein's Sonata, a multimedia project devoted to the artistic public display of the LISA data. Einstein's Sonata features as its main element the piece Periplo del latte. The latter is based on mapping astronomical data onto music. We thus detail a four-stage procedure for algorithmic composition, that features two data preprocessing stages, a mapping into an abstract control space and finally automatic notation generation.