If there are only two CMGs in the cluster, as in our first example, then anti-parallel alignment will inevitably occur if the total stored angular momentum reaches zero. The remedy is to keep it away from zero, possibly by using RCS firings. This is not very satisfactory, and in practice all spacecraft using CMGs are fitted with at least three. However it sometimes happens that after malfunctions a cluster is left with only two working CMGs, and the control program must be able to deal with this situation.