Senior Software Engineer NextGen Federal Systems, LLC is seeking a Software Engineer with experience in Systems Tool Kit (STK) to support the development and integration of mission analysis and modeling applications. These applications enable multi-domain analysis—including air, space, ground, and maritime systems—by leveraging physics-based modeling and simulation to assess system performance, coverage, communications, and operational effectiveness. Responsibilities include software development, configuration, and execution; result interpretation; documentation; and modification and maintenance of tools and code. The selected candidate must be quick to learn, adaptable, and agile, interfacing directly with end-customers and customer leadership. The software engineer will provide a full range of systems and software engineering to support critical mission analyses. \nResponsibilities Develop, customize, and maintain STK-based applications to support mission planning, analysis, and visualization Integrate STK (Engine, Components, or Desktop) with external tools, models, and data sources to enable end-to-end mission workflows Implement backend services using Python and support frontend interfaces as needed Analyze and interpret simulation results, providing actionable insights to engineering teams and stakeholders Support traceability between mission analysis outputs and system models, ensuring consistency across the digital engineering environment Support deployment and execution of applications in modern environments (e.g., containerized or cloud-based) Contribute to documentation, user guides, and technical deliverables Troubleshoot and enhance existing tools to improve performance, usability, and scalability Qualifications BS or equivalent in Computer Science, Engineering, Mathematics, or equivalent technical degree 5+ years’ prior work experience in the aerospace or defense industry, with demonstrated software development experience Experience customizing or automating STK-based tools or applications highly desired (including STK, STK Engine, STK Components, and/or Cesium) Experience integrating tools via APIs (REST or similar) Proficiency in Python and experience with backend frameworks such as Flask is required Strong expertise in React JS for building modern and responsive user interfaces is highly desirable Knowledge of version control systems, preferably Git is highly desirable Proven experience as a Full Stack Developer or similar role is highly desirable Capable of self-management and responsibly executing multiple tasks in accordance with priorities and deadlines Active Top Secret (TS) clearance required (SCI eligibility preferred) Preferred Qualifications Experience with STK Engine, STK Components, or Cesium Experience linking STK analyses to MBSE environments (e.g., parameter passing, trade studies, digital thread integration) Familiarity with digital engineering ecosystems, mission thread development, or model orchestration tools Experience with Docker, cloud environments, or DevSecOps practices Frontend development experience (e.g., React) \n About NextGen: NextGen Federal Systems is an innovative technology and professional services provider specializing in advanced software solutions and comprehensive mission and business support services. We work in close collaboration with our customers to truly understand their business and mission goals. Our approach is to design, build, implement, and manage solutions that measurably improve our client’s organizational performance. We have established and foster a corporate culture where we: Treat employees with fairness and respect regardless of their position, sexual identity, race, or tenure. Communicate the importance of our mission and our employees’ contributions to it, ensuring they understand how their job role contributes to the greater good. Openly promote and communicate our ideas for change and adaptability. Strive to achieve results as an organization. Hold employees accountable to their commitments and provide incentives that encourage positive and productive behaviors. Value the talents and contributions of our employees as the key factor for our success. Create an environment where people can engage at all levels. Encourage people to take risks and allow them to make mistakes. Equal Opportunity Employer/Protected Veterans/Individuals with Disabilities.