A sub-scale solid rocket motor designed to mimic NASA's Space Launch System, or SLS, booster design successfully was tested today by engineers at NASA's Marshall Space Flight Center in Huntsville, Ala.  The 20-second firing tested new insulation materials on the 24-inch-diameter, 109-inch-long motor.  The motor is a scaled down, low-cost replica of the solid rocket motors that will boost SLS off the launch pad.