  The requirements on space missions designed to study Terrestrial exoplanets
are discussed. We then investigate whether the design of such a mission,
specifically the Darwin nulling interferometer, can be carried out in a
simplified scenario. The key element here is accepting somewhat higher levels
of stellar leakage. We establish detailed requirements resulting from the
scientific rationale for the mission, and calculate detailed parameters for the
stellar suppression required to achieve those requirements. We do this
utilizing the Darwin input catalogue. The dominating noise source for most
targets in this sample is essentially constant for all targets, while the
leakage diminishes with the square of the distance. This means that the stellar
leakage has an effect on the integration time only for the nearby stars, while
for the more distant targets its influence decreases significantly. We assess
the impact of different array configurations and nulling profiles and identify
the stars for which the detection efficiency can be maximized.
