The Micro-X sounding rocket payload will be launched on January 18, 2011 to make the first observation of an astronomical target with Transition-Edge Sensor (TES) X-ray microcalorimeters. The 128 pixel TES array lies at the focus of a 2.165 m focal length conical imaging mirror with a 0.2-3.0 keV bandpass. The spectral resolution of the TES array will be between 2 and 4 eV at 1 keV. Our scientific program is focused on high-spectral resolution observations of extended sources. For supernova remnants (SNRs) our scientific objectives are to map the velocity structure of the ejecta, and study both elemental abundances and the thermodynamic and ionization state of the plasma through plasma line diagnostics. For clusters of galaxies, Micro-X can uniquely study turbulence, velocities, and the temperature phases of the plasma. For our initial flight, we have changed our target from the bright eastern knot to a recently discovered ejecta region in the Puppis A SNR. The target of the second flight in mid-2012 is M87, the center of the Virgo Cluster. The third flight, in early 2014, will make an observation of the Cas A SNR. In this contribution we discuss the science objectives of our first flight.