Mission Software Engineer

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. Mission Software Engineer Castelion is seeking a Mission Software Engineer to build the software that connects our products into an integrated mission capability. Mission Software spans Castelion’s full product portfolio, including weapons, launchers, command-and-control systems, sensors, mission planning tools, and external platforms. Engineers on this team build the software that allows operators and systems to plan missions, exchange targeting and sensor data, command assets, initialize and employ weapons, and execute missions end to end. This is a hands-on software engineering role. You will design, write, review, test, and commit production code to Castelion’s software stack while working closely with flight software, avionics, guidance and navigation, systems engineering, test, and integration teams. The work crosses traditional software boundaries. You may be developing mission planning software, integrating a tactical C2 interface, building services that move targeting data between systems, debugging communication between a launcher and weapon, or supporting an integrated flight test. Core Responsibilities • Design, develop, test, and deploy production software supporting weapons, launchers, C2 systems, sensors, and mission planning. • Develop and integrate command-and-control software connecting operators, sensors, weapons, launchers, tactical networks, and external platforms. • Build APIs, services, and data pipelines that move targeting, mission, telemetry, and system-state data throughout the mission architecture. • Develop software interfaces between Castelion products and aircraft, launchers, mission computers, fire-control systems, sensors, and government C2 systems. • Implement communications across interfaces and protocols such as Ethernet, TCP/UDP, CAN, MIL-STD-1553, MIL-STD-1760, and other tactical interfaces. • Translate operational concepts, system requirements, and ICDs into scalable software architectures and working implementations. • Develop simulators, tools, and test infrastructure for software-in-the-loop, hardware-in-the-loop, and system-level testing. • Debug complex issues spanning application software, embedded systems, networks, avionics, sensors, and hardware. • Contribute production code using modern Git-based workflows, code review, automated testing, and continuous integration. • Support integration and test activities from laboratory testing through ground and flight test. • Work directly with government customers, platform partners, operators, and other engineering teams during integration and fielding. • Own software capabilities from initial architecture through implementation, test, deployment, and operational use. Basic Qualifications • Bachelor's degree in Computer Science, Computer Engineering, Electrical Engineering, Aerospace Engineering, or a related technical field. • 3+ years of professional software engineering experience. • Strong software development experience in C++, Rust, Python, Go, C, or similar languages. • Experience contributing to a production software codebase using Git, code review, automated testing, and CI/CD. • Strong understanding of software architecture, APIs, networking, data serialization, concurrency, and distributed systems. • Experience developing software that interfaces with hardware, embedded systems, or external services. • Experience debugging complex integrated software systems. • Ability to independently take software capabilities from requirements and architecture through implementation and test. • Strong communication skills and the ability to work across software, hardware, systems, and operations teams. • Ability to obtain and maintain a U.S. security clearance. Preferred Skills and Experience • Experience developing mission planning, C2, fire control, targeting, autonomy, sensor integration, or weapon-system software. • Experience with weapons, launchers, aircraft avionics, autonomous systems, spacecraft, robotics, or other mission-critical systems. • Experience with MIL-STD-1553, MIL-STD-1760, UAI, CAN, Ethernet, TCP/UDP, protobuf, tactical data links, or military mission systems. • Experience with geospatial software, coordinate systems, targeting, route planning, trajectory generation, or mission-data processing. • Experience developing software that integrates sensors, shooters, operators, and command-and-control systems. • Experience with embedded or real-time software. • Experience developing Linux-based applications and services. • Experience with SIL, HIL, vehicle-in-the-loop, or flight-test environments. • Experience supporting complex system-level integration and test campaigns. • Active Secret or Top Secret clearance. Additional Requirements • Ability to put in extended hours, including evenings and weekends, when required to meet aggressive timelines • This role is based in Torrance, CA and requires full-time onsite presence What Success Looks Like You will own software that connects Castelion systems across the mission — from sensing and targeting through mission planning, C2, launch, and weapon employment. Your work will move from architecture and production code into integrated system test, flight test, and operational fielding. You will help define how Castelion’s products communicate and operate together as a complete mission system. 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 abili