  We study a space-based gravity gradiometer based on cold atom interferometry
and its potential for the Earth's gravitational field mapping. The instrument
architecture has been proposed in [Carraz et al., Microgravity Science and
Technology 26, 139 (2014)] and enables high-sensitivity measurements of gravity
gradients by using atom interferometers in a differential accelerometer
configuration. We present the design of the instrument including its subsystems
and analyze the mission scenario, for which we derive the expected instrument
performances, the requirements on the sensor and its key subsystems, and the
expected impact on the recovery of the Earth gravity field.
