Detection limits in space-based transit observations
  From simulations of transit observations, it is found that the detectability of extrasolar planets depends only on two parameters: The signal-to-noise ratio during a transit, and the number of data points observed during transits. All other physical parameters describing transit configurations (planet and star size, orbital period, orbital half axis, latitude of the transit across star) can be reduced to these two parameters. In turn, once the dependency between transit detectability and these two parameters has been determined, predictions for an instrument's ability to detect transits by any combination of physical parameters can be derived with ease. These predictions are applied to the Eddington proposal of a combined Astroseismology/Transit-detection space mission currently under study by ESA, which is described briefly. 
H.J. Deeg, F. Favata, and Eddington Science Team