Software Engineer

About the job Software Engineer - Platform Integration

About Castelion

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.

Software Engineer - Platform Integration

Castelion is seeking a Software Engineer - Platform Integration, to develop embedded and integration-layer software that enables Castelion's hypersonic weapon systems to interface with a variety of airborne and ground-based launch platforms. This includes implementing Universal Armament Interface (UAI) protocols for tactical aircraft and supporting Fire Control System (FCS) integration for ground-based launchers.

You will contribute to the full lifecycle of integration, from protocol implementation and system communication to simulation, testing, and mission deployment. The ideal candidate is a generalist with strong software fundamentals, experience working across embedded and systems layers, and a drive to build real-world, high-performance systems.

Responsibilities

• Develop and validate software interfaces using UAI, MIL-STD-1760, MIL-STD-1553, and CANbus.
• Support integration with Fire Control Systems (FCS) and Operational Flight Programs (OFPs) to enable real-time command & control.
• Translate Interface Control Documents (ICDs) into clear, testable software modules that meet timing, safety, and operational requirements.
• Build and maintain hardware-in-the-loop (HIL) and software-in-the-loop (SIL) test environments for simulation and validation.
• Work cross-functionally with avionics, GNC, and mission software teams to ensure end-to-end system integration and performance.
• Participate in lab, simulation, and field testing of integrated weapon systems.

Basic Qualifications

• Bachelor's degree in Computer Science, Electrical/Computer Engineering, or a related field.
• 3+ years of professional experience in software engineering.
• Proficiency in one or more modern programming languages such as Python, C++, Rust, Go, or JavaScript.
• Familiarity with embedded systems, communication protocols, and hardware/software integration.
• U.S. Citizenship and eligibility for a Top Secret/SCI clearance.

Preferred Skills and Experience

• Experience working with defense/aerospace protocols such as UAI, MIL-STD-1553, MIL-STD-1760, or CANbus.
• Exposure to avionics, payload integration, or weapons interface development.
• Hands-on experience with SIL/HIL test environments.
• Active Top Secret/SCI clearance.

Why This Role Matters

• Your work ensures that advanced weapon systems can communicate, respond, and perform in real-world operational environments. The interfaces you build will directly enable mission success.

Leadership Qualities

• Bias to Action and Creative Problem Solving. Desire and experience questioning assumptions in ways that lead to break through ideas that are ultimately implemented. Successfully bring in applicable processes/concepts/materials from other industries to achieve efficiency gains. The 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.

All employees are granted long-term stock incentivesas part of their employment at Castelion. All employees receive access tocomprehensive medical, vision, and dental insurance, and the company offersfour weeks of paid time off per year.

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