Senior Simulation Software Engineer, GNC

Why Castelion, Why Now Castelion is moving incredibly fast to develop and deliver advanced defense systems at a time when execution matters more than ever. We believe focus, ownership, and excellence are decisive advantages - and we're building a world-class team to turn bold ideas into real capability. This is a rare opportunity to join at an early stage, where you'll have significant ownership, collaborate with exceptional teammates, and make a direct, measurable impact on our mission and the future of the company - regardless of your function. Senior Simulation Software Engineer, GNC We're looking for a GNC Simulation Software Engineer to design, develop, and maintain high-fidelity simulation software supporting missile guidance, navigation, and control (GNC) development. In this role, you'll work closely with GNC algorithm developers, flight software engineers, and test teams to create fast, accurate, and robust simulations that drive system architecture decisions, performance assessments, and mission success. Responsibilities • Develop and maintain a 6-DoF missile simulation software platform. • Build scalable infrastructure to execute, manage, and aggregate data from Monte Carlo campaigns, along with automated performance evaluation tools. • Ensure appropriate configuration management and shared sources of truth between simulation and flight code. • Optimize software for real-time or hardware-in-the-loop (HITL) execution where required. • Develop robust testing, verification, and documentation practices to ensure reliability and correctness. • Support flight software integration, pre-flight analysis, and post-flight reconstruction. Basic Qualifications • Bachelors or Masters degree in computer engineering, computer science, aerospace engineering, or a related field. • Strong proficiency in C++ or Rust for high-performance numerical modeling. • Proficiency with databases and large data structures. • Familiarity with version control, CI/CD pipelines, and modern software engineering practices. • Experience with numerical integration, coordinate transformations, and simulation architecture. • Experience with software integration, specifically linking disparate software modules (e.g., embedding Rust code in C++, Python bindings for C++ libraries). • Familiarity with GNC concepts in aerospace or missile systems. • Ability to develop well-structured, scalable, and efficient code. Preferred Skills and Experience • Experience with missile dynamics, aerodynamics, or propulsion modeling. • Background in Monte Carlo simulation pipelines and statistical analysis. • Experience with hardware-in-the-loop or real-time simulation. • Exposure to sensor modeling (IMU, GPS, radar, seekers) or actuator modeling (TVC, CAS). • Experience integrating simulations with GNC or embedded flight software environments. • Experience designing APIs or internal tools for engineering teams. Castelion offers a generous benefits package. Please refer to the bottom of our Careers page for more details. Other Duties Please note this job description is not designed to cover or contain a comprehensive listing of activities, duties or responsibilities that are required of the employee for this job. Duties, responsibilities and activities may change at any time with or without notice. Additional Eligibility Requirements This position may require access to classified information or restricted U.S. Government sites, systems, or information, as determined by the Company and/or applicable U.S. Government requirements. If the position is so designated, your employment in the role may be contingent upon your ability to obtain and maintain the required U.S. Government security clearance or other government authorization, and to satisfy any citizenship or other eligibility requirements imposed by applicable law, regulation, executive order, or government contract requirements. You will be notified if and when such requirements apply. Affirmative Action/EEO Statement Castelion is an Equal Opportunity Employer. We are committed to providing equal employment opportunities to all applicants and employees without regard to race, color, religion, sex, sexual orientation, gender identity, national origin, age, disability, genetic information, protected veteran status, or any other characteristic protected by applicable federal, state, or local law. Castelion is committed to providing reasonable accommodations to qualified individuals with disabilities throughout the application and hiring process. If you require a reasonable accommodation to complete an application, participate in the interview process, or otherwise participate in the hiring process, please contact hr@castelion.com. Requests for accommodation will be considered on an individual basis and handled in accordance with applicable law. Castelion is committed to fostering a workplace where employment decisions are based on qualifications, business needs, and the ability to perform the essential functions of the role, with or without reasonable accommodation. EAR/ITAR Requirements This position requires access to export-controlled information, and as such, employment (or hiring of a contractor) is contingent upon the candidate’s ability to access all applicable export-controlled information without additional export licensing being required by the Bureau of Industry and Security and/or the Directorate of Defense Trade Controls.