  The surface composition of S-type asteroids can be determined using band
parameters extracted from their near-infrared (NIR) spectra (0.7-2.50 $\mu$m)
along with spectral calibrations derived from laboratory samples. In the past,
these empirical equations have been obtained by combining NIR spectra of
meteorite samples with information about their composition and mineral
abundance. For these equations to give accurate results, the characteristics of
the laboratory spectra they are derived from should be similar to those of
asteroid spectral data (i.e., similar signal-to-noise ratio (S/N) and
wavelength range). Here we present new spectral calibrations that can be used
to determine the mineral composition of ordinary chondrite-like S-type
asteroids. Contrary to previous work, the S/N of the ordinary chondrite spectra
used in this study has been decreased to recreate the S/N typically observed
among asteroid spectra, allowing us to obtain more realistic results. In
addition, the new equations have been derived for five wavelength ranges
encompassed between 0.7 and 2.50 $\mu$m, making it possible to determine the
composition of asteroids with incomplete data. The new spectral calibrations
were tested using band parameters measured from the NIR spectrum of asteroid
(25143) Itokawa, and comparing the results with laboratory measurements of the
returned samples. We found that the spectrally derived olivine and pyroxene
chemistry, which are given by the molar contents of fayalite (Fa) and
ferrosilite (Fs), are in excellent agreement with the mean values measured from
the samples (Fa$_{28.6\pm1.1}$ and Fs$_{23.1\pm2.2}$), with a maximum
difference of 0.6 mol\% for Fa and 1.4 mol\% for Fs.
