  We introduce a stellar velocity survey of dwarf spheroidal galaxies,
undertaken using the Michigan/MIKE Fiber System (MMFS) at the Magellan/Clay 6.5
m telescope at Las Campanas Observatory. As of 2006 November we have used MMFS
to collect 6415 high-resolution (R= 20000-25000) spectra from 5180 stars in
four dwarf spheroidal galaxies: Carina, Fornax, Sculptor and Sextans. Spectra
sample the range 5140-5180 Angstroms, which includes the prominent magnesium
triplet absorption feature. We measure radial velocity (RV) to a median
precision of 2.0 km/s for stars as faint as V ~ 20.5. From the spectra we also
are able to measure the strength of iron and magnesium absorption features
using spectral indices that correlate with effective temperature, surface
gravity and chemical abundance. Measurement of line strength allows us to
identify interloping foreground stars independently of velocity, and to examine
the metallicity distribution among dSph members. Here we present detailed
descriptions of MMFS, our target selection and spectroscopic observations, the
data reduction procedure, and error analysis. We compare our RV results to
previously published measurements for individual stars. In some cases we find
evidence for a mild, velocity-dependent offset between the RVs we measure using
the magnesium triplet and previously published RV measurements derived from the
infrared calcium triplet. In companion papers we will present the complete data
sets and kinematic analyses of these new observations.
