  We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray timing
and spectroscopy of the three exceptionally energetic rotation-powered
millisecond pulsars PSRs B1821-24, B1937+21, and J0218+4232. By correcting the
NuSTAR onboard clock for phase and frequency drifts between observation
intervals, we are able to recover the intrinsic hard X-ray pulse profiles of
all three pulsars with a resolution down to < 15 microsec. The substantial
reduction of background emission relative to previous broadband X-ray
observations allows us to detect for the first time pulsed emission up to ~50
keV, ~20 keV, and ~25 keV, for the three pulsars, respectively. We conduct
phase-resolved spectroscopy in the 0.5-79 keV range for all three objects,
obtaining the best measurements yet of the broad-band spectral shape and
high-energy pulsed emission to date. We find extensions of the same power-law
continua seen at lower energies, with no evidence for a spectral turnover or
break. Extrapolation of the X-ray power-law spectrum to higher energies reveals
that a turnover in the 100 keV to 100 MeV range is required to accommodate the
high-energy gamma-ray emission observed with Fermi-LAT, similar to the spectral
energy distribution observed for the Crab pulsar.
