Senior Simulation Software Engineer, GNC

Senior Simulation Software Engineer, GNC Torrance, California, United States About the Job Senior Simulation Software Engineer, GNC Castelion is bringing a new approach to defense development and production: one that focuses on short, iterative design cycles, rapid testing in development, and modern commercial manufacturing strategies for production at scale. We're designing, building, and testing next generation long range strike weapons systems to give America and its Allies a definitive edge and deter future conflicts. 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. All employees are granted long-term stock incentives as part of their employment at Castelion. All employees receive access to comprehensive medical, vision, and dental insurance, and the company offers four weeks of paid time off per year. Leadership Qualities Bias to Action and Creative Problem Solving. Desire and experience questioning assumptions in ways that lead to breakthrough ideas that are ultimately implemented. Successfully bring in applicable processes/concepts/materials from other industries to achieve efficiency gains. Ability to personally resolve minor issues in development without requiring significant support. High Commitment, High Initiative. A successful candidate will have a genuine passion for Castelion's mission and consistently look for ways to contribute to the company's technical goals and prevent hardware blockers. Ability to work in a fast paced, autonomously driven, and demanding atmosphere. Strong sense of accountability and integrity. Clear Communicator. Proactively communicates blockers. Trusted in previous roles to be voice of company with regulators, suppliers, gate keepers and customers. Capable of tactfully managing relationships with stakeholders to achieve company-desired outcomes without compromising relationships. Emails, IMs and verbal interactions are logical, drive clarity, and detailed enough to eliminate ambiguity. ITAR Requirements: To conform to U.S. Government export regulations, applicant must be a (i) U.S. citizen or national, (ii) U.S. lawful, permanent resident (aka green card holder), (iii) Refugee under 8 U.S.C. § 1157, or (iv) Asylee under 8 U.S.C. § 1158, or be eligible to obtain the required authorizations from the U.S. Department of State. Employment with Castelion is governed on the basis of competence and qualifications and will not be influenced in any manner by race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability or any other legally protected status. Castelion