  We calculate the spectra of ultra-high-energy cosmic rays (UHECRs) in an
explicit top-down model based on the decays of metastable neutral `crypton'
states in a flipped SU(5) string model. For each of the eight specific
10th-order superpotential operators that might dominate crypton decays, we
calculate the spectra of both protons and photons, using a code incorporating
supersymmetric evolution of the injected spectra. For all the decay operators,
the total UHECR spectra are compatible with the available data. Also, the
fractions of photons are compatible with all the published upper limits, but
may be detectable in future experiments.
