BM3 periods in the 2005 tail constellation

This page describes the algorithm used to schedule BM3 periods during the 2005 tail constellation of the Cluster spacecraft. The basic principle is the same as that for the 2002 tail constellation. Thus we place these periods in the lobes, away from both (a) the perigee/interior cusp region and (b) the tail neutral sheet. Thus we place one BM3 period in the northern lobe between perigee and the neutral sheet crossing and one in the southern lobe between the neutral sheet and the next perigee. This is illustrated in the figure below, which uses a Bryant plot format to show the locations of the predicted neutral sheet crossing (s/c 1) and the BM3 periods.

The figure shows that the orbit phase of the Cluster neutral sheet crossing has a systematic trend towards earlier orbit phases, with some scatter due to the diurnal motion of the model neutral sheet (driven by the diurnal motion of the geomagnetic dipole). The correlation coefficient (R2=0.628) and trendline for a linear fit are given in the figure.

The BM3 periods follow this trendline with one period scheduled 10 hours before the trendline and the other 28.5 hours (half an orbit) after the first. This approach yields two BM3 periods per orbit with adequate time margins to avoid overlap with key targets such as the neutral sheet and the cusp. In the worst cases, the BM3 periods are scheduled about 5 hours from perigee.

Caveats

Last updated 28 June 2005 by Mike Hapgood