  We studied asteroid clusters suggesting a possibility of at least two
disruption events in their recent history (< 5 Myr). We searched for new
members of known asteroid pairs and clusters and we verified their membership.
We found four asteroid clusters, namely the clusters of (11842) Kap'bos,
(14627) Emilkowalski, (63440) 2001 MD30 and (157123) 2004 NW5 that show at
least two secondary separation events that occurred at significantly different
times. We considered a possible formation mechanism for these clusters: The
parent of an asteroid cluster was spun up to its critical rotation frequency,
underwent a rotation fission and was slowed down by escape of the newly formed
secondary/ies. Then the YORP effect spun up the primary again and it reached
its critical rotation frequency and underwent another fission. We created a
simple model to test whether this scenario is possible for the four clusters.
We obtained a good agreement between the model and the cluster properties for
the clusters of Kap'bos and (63440). For the cluster of Emilkowalski, the time
needed for the primary to reach its critical frequency after the first fission
event was predicted to be too long by a factor of several. We suspect,
considering also its D type taxonomic classification and the existence of a
dust band associated with the cluster, that the asteroid Emilkowalski may
actually be a cometary nucleus. For the cluster of (157123), the final
rotational frequency of the primary after the last fission event predicted by
our model is in a good agreement with the observed rotation frequency of
(157123). However, a separation of the older secondary is not possible in our
model due to the deficiency of free energy needed for an escape of the large
secondary. This could be due to an error in the H value of the secondary or the
possibility that we did not find the real primary of this cluster.
