Small unmanned aircraft system (sUAS) as defined by the Federal Aviation Administration (FAA) refers to a small unmanned aircraft weighing less than 55 pounds on takeoff, and its associated elements that are required for the safe and efficient operation of the small unmanned aircraft in the national airspace system. The unmanned aircraft system (UAS) traffic management (UTM) system is envisioned by the National Aeronautics and Space Administration (NASA) to enable civilian low-altitude airspace and UAS operations by providing services such as airspace design, corridors, dynamic geofencing, severe weather and wind avoidance, congestion management, terrain avoidance, route planning and re-routing, separation management, sequencing and spacing, and contingency management. Trajectory modeling and prediction methods are foundational capabilities in support of UTM to achieve its goals. This paper presents a framework for the development and validation of trajectory modeling and prediction methods for diverse types of sUASs under nominal environment and under a variety of realistic potential hazards, including adverse environmental conditions, and vehicle and system failures. Results from initial analysis of major components of the framework are also presented. Detailed results from the development and validation will be reported in subsequent papers as the research progresses.