  The pre-launch event simulation and reconstruction performed beyond our
expectations for real data, essentially without modification, and made possible
the immediate start of science analysis. But the on-orbit data exhibit
unanticipated features that necessitate upgrades to both the simulation
(essentially complete) and the reconstruction (ongoing). The major new effect
encountered on orbit is the presence of "ghosts," that is, remnant detector
response to particles passing through the detector before the particle that
triggered the event. These ghosts appear primarily in the form of extra tracks
and/or energy deposits. As part of this upgrade, we plan to enhance our ability
to discriminate against background particles by introducing additional analysis
during the reconstruction phase. We present a description of the effect of
ghosts, and of the work needed to deal with them, done and planned, as well as
some other ideas for improving the reconstruction.
