This article discusses the developmental challenges of the low-thrust, long-duration solid rocket motor for the launch of the experimental Reusable Launch Vehicle-Technological Demonstrator (RLV-TD). The main challenges were: (1) developing a motor case and subsystems with low inert mass; (2) design of an optimum nozzle such that the motor can have maximum specific impulse at atmospheric conditions, but with no flow separation at low operation pressures; (3) developing a slow-burning propellant (3 mm/s) to meet the mission requirements; (4) design of propellant grain for the motor so that it has long burning time, the vehicle experiences low dynamic pressure at the transonic regime, and the motor is without combustion instability; (5) developing necessary thermal protection system to take care of long-duration operations, and (6) developing the igniter to ensure the ignition of the motor, especially when easy ignition is difficult with slow-burning propellants and that there should be sufficient overlap of igniter functioning with motor initiation. Performance of the motor in flight indicated that the design met all the required criteria within the expected tolerance.