  The B-mode polarisation power spectrum in the Cosmic Microwave Background
(CMB) is about four orders of magnitude fainter than the CMB temperature power
spectrum. Any instrumental imperfections that couple temperature fluctuations
to B-mode polarisation must therefore be carefully controlled and/or removed.
We investigate the role that a scan strategy can have in mitigating certain
common systematics by averaging systematic errors down with many crossing
angles. We present approximate analytic forms for the error on the recovered
B-mode power spectrum that would result from differential gain, differential
pointing and differential ellipticity for the case where two detector pairs are
used in a polarisation experiment. We use these analytic predictions to search
the parameter space of common satellite scan strategies in order to identify
those features of a scan strategy that have most impact in mitigating
systematic effects. As an example we go on to identify a scan strategy suitable
for the CMB satellite proposed for the ESA M5 call. considering the practical
considerations of fuel requirement, data rate and the relative orientation of
the telescope to the earth. Having chosen a scan strategy we then go on to
investigate the suitability of the scan strategy.
