Original approved PhD thesis, full-color paperback, 155 pages plus appendices. This PhD thesis shows how gravity is mediated by the deformation of spacetime. Accelerated matter produces gravitational radiation that travels in waves unimpeded throughout the entire universe. A detailed analysis of these waves will bring the next big revelations in astronomy, cosmology, and fundamental physics alike. The gravitational wave observatory planned by the European Space Agency covers the most rewarding range of frequencies and enables us to directly study black holes, neutron stars, and even the echo of the Big Bang itself. The PhD thesis further determines the sensitivity of spaceborne gravitational wave observatories. It considers the detailed instrument design and re-evaluates important requirements for different on-board systems. Within the limits of current technology, some of these requirements - like the timing stability of reference oscillators - cannot be met directly. For this reason, an additional system was developed that synchronizes all measurements between spacecraft. It was tested successfully and meets even the strictest timing requirements.