  We present Space Telescope Imaging Spectrograph (STIS) spectral images of the
HH~30 stellar jet taken through a wide slit over two epochs. The jet is
unresolved spectrally, so the observations produce emission-line images for
each line in the spectrum. This rich dataset shows how physical conditions in
the jet vary with distance and time, produces precise proper motions of knots
within the jet, resolves the jet width close to the star, and gives a spectrum
of the reflected light from the disk over a large wavelength range at several
positions. We introduce a new method for analyzing a set of line ratios based
on minimizing a quadratic form between models and data. The method generates
images of the density, temperature and ionization fraction computed using all
the possible line ratios appropriately weighted. In HH 30, the density declines
with distance from the source in a manner consistent with an expanding flow,
and is larger by a factor of two along the axis of the jet than it is at the
periphery. Ionization in the jet ranges from ~ 5% to 40%, and high
ionization/excitation knots form at about 100 AU from the star and propagate
outward with the flow. These high-excitation knots are not accompanied by
corresponding increases in the density, so if formed by velocity variations the
knots must have a strong internal magnetic pressure to smooth out density
increases while lengthening recombination times.
