Introduction T HE ignition transient of a solid rocket motor (SRM) employing a pyrogen igniter can be defined as the time interval from the onset of the igniter flow to the time a quasisteady flow develops. A little-understood portion of the starting transient for (star) slotted head-end grain configurations is the time interval encompassing the initiation of the igniter flow, the first appearance of a flame on the star grain, and the subsequent flame spread over the star slot region. Previous analyses' for motors such as those used on the Space Shuttle agree quantitatively well with test data, except for the time period that directly involves burning of the headend star grain segment. Discrepancies during this time period are believed to arise from three factors: 1) the flowfield is assumed to be one-dimensional, 2) the star geometry in the head-end segment is approximated by variations in port area and grain burning perimeter, and 3) the igniter flowfield is not accounted for. The authors have previously presented a numerical calculation method utilizing the time-dependent, two-dimensional Navier-Stokes equations, which calculates the subsonic flow induced in the slot by the supersonic igniter plume. The focus of the present study is the calculation of the initial portion of the ignition transient, beginning with the start of igniter flow and ending when the head-end star slot segment of the motor is fully burning. The expanding igniter plume, the complex flow patterns within the star slot, heat transfer to the propellant grain, and subsequent propellant burning are considered.