NASA Unmanned Traffic Management Program (UTM) and its early builds focus on requirements for fixed geofencing and low-altitude UAS without interaction with manned flights. However, later builds will require functionality for operation in dynamic missions employing multiple collaborating UAS in mixed manned-unmanned teams, and in environments where pre-specified geofencing, flight planning, and separation rules are not applicable. To address this challenge, SSCI proposes to develop, implement and test an innovative ON-DEMAND (Operations in Dynamic Environments with Manned And Unmanned Aircraft Deconfliction) system, a portable ATC center, whose role will be to monitor the environment, predict the environmental changes, and approve new geofencing boundaries, new manned-unmanned vehicle separation boundaries, and new flight plans in real-time while avoiding conflicts and assuring overall system safety. Specific system functions will include: (i) Prediction and adjustment of the geofence boundaries based on user requests or environmental changes; (ii) Prediction of the effects of user commands which may generate potential conflicts between manned and unmanned aircraft; and (iii) Dynamic mission re-planning, requiring real-time generation of new flight-plans under separation assurance guidelines. The main project objective is to develop requirements for the design and implementation of a local ATC for dynamically varying environments. We plan to propose an effective mission and flight plan re-planning approach, and effective conflict monitoring and resolution procedures which will enable smooth mission operation while assuring overall system safety. Under the project SSCI will leverage its state-of-the-art flight path prediction routines, collision detection and avoidance system, and system-level safety evaluation approach. Phase I will also include simulation testing and flight data collection with our partners at Olin College of Engineering.