  The high time resolution observations of the X-ray sky hold the key to a
number of diagnostics of fundamental physics, some of which are unaccessible to
other types of investigations, such as those based on imaging and spectroscopy.
Revealing strong gravitational field effects, measuring the mass and spin of
black holes and the equation of state of ultradense matter are among the goals
of such observations. At present prospects for future, non-focused X-ray timing
experiments following the exciting age of RXTE/PCA are uncertain. Technological
limitations are unavoidably faced in the conception and development of
experiments with effective area of several square meters, as needed in order to
meet the scientific requirements. We are developing large-area monolithic
Silicon Drift Detectors offering high time and energy resolution at room
temperature, which require modest resources and operation complexity (e.g.,
read-out) per unit area. Based on the properties of the detector and read-out
electronics that we measured in the lab, we developed a realistic concept for a
very large effective area mission devoted to X-ray timing in the 2-30 keV
energy range. We show that effective areas in the range of 10-15 square meters
are within reach, by using a conventional spacecraft platform and launcher of
the small-medium class.
