It is widely argued that today's largely reactive, “respond and patch” approach to securing cyber systems must yield to a new, more rigorous, more proactive methodology. Achieving this transformation is a difficult challenge. Building on insights into requirements for cyber science and on experience gained through 8 years of operation, the DETER project is addressing one facet of this problem: the development of transformative advances in methodology and facilities for experimental cybersecurity research and system evaluation. These advances in experiment design and research methodology are yielding progressive improvements not only in experiment scale, complexity, diversity, and repeatability, but also in the ability of researchers to leverage prior experimental efforts of others within the community. We describe in this paper the trajectory of the DETER project towards a new experimental science and a transformed facility for cyber-security research development and evaluation.