  We describe the ``Monitor e Imageador de Raios-X'' (MIRAX), an X-ray
astronomy satellite mission proposed by the high energy astrophysics group at
the National Institute for Space Research (INPE) in Brazil to the Brazilian
Space Agency. MIRAX is an international collaboration that includes, besides
INPE, the University of California San Diego, the University of Tuebingen in
Germany, the Massachusetts Institute of Technology and the Space Research
Organization Netherlands. The payload of MIRAX will consist in two identical
hard X-ray cameras (10 -200 keV) and one soft X-ray camera (2-28 keV), both
with angular resolution of ~ 5-6 arcmin. The basic objective of MIRAX is to
carry out continuous broadband imaging spectroscopy observations of a large
source sample (~ 9 months/yr) in the central Galactic plane region. This will
allow the detection, localization, possible identification, and
spectral/temporal study of the entire history of transient phenomena to be
carried out in one single mission. MIRAX will have sensitivities of ~ 5
mCrab/day in the 2-10 keV band (~2 times better than the All Sky Monitor on
Rossi X-ray Timing Explorer) and 2.6 mCrab/day in the 10-100 keV band (~40
times better than the Earth Occultation technique of the Burst and Transient
Source Experiment on the Compton Gamma-Ray Observatory). The MIRAX spacecraft
will weigh about 200 kg and is expected to be launched in a low-altitude (~ 600
km) circular equatorial orbit around 2007/2008.
