Mechanical Engineer Fall 2026 Co-Op

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. Fall 2026 Mechanical Engineering Co-Op Join us for a dynamic, hands-on experience developing next-generation missile systems. As an intern, you'll contribute directly to the design, testing, and integration of advanced defense technologies all within a fast-paced, collaborative startup environment where your work has immediate impact. Key Responsibilities: Assist in the design, analysis, and testing of components for missile subsystems, including propulsion, guidance systems, power electronics, and more. Support engineering teams with simulations, modeling, and prototyping of critical hardware components. Conduct research and development tasks, gathering and analyzing data to inform design decisions. Participate in system integration efforts, helping to assemble and test subsystems in real-world test environments. Collaborate cross-functionally with engineering, manufacturing, and test teams to ensure project success. Document design processes, test results, and project progress, contributing to the continuous improvement of our systems. Attend technical reviews, design meetings, and team briefings to stay engaged with project developments and learn from industry experts. Learning Opportunities: Gain hands-on experience in aerospace engineering, working on cutting-edge hypersonic missile systems. Develop your technical skills by working with high-performance teams and state-of-the-art tools. Learn about the full lifecycle of missile development, from design and prototyping to testing and final integration. Receive mentorship from experienced engineers and leaders in the aerospace and defense industry. Be a part of a fast-paced startup culture where innovation, teamwork, and rapid development are at the forefront. Qualifications: Currently pursuing a Bachelor's or Master's degree in Mechanical Engineering, Aerospace Engineering, or a related field. Rising junior, senior, or graduate-level student preferred. Strong academic record with relevant coursework in areas such as mechanical design, propulsion, power systems, or related fields Hands-on experience through lab work, projects, or internships is a plus. Passion for aerospace, defense technology, and innovative engineering solutions. Excellent problem-solving, analytical, and communication skills. Ability to work collaboratively in a fast-paced, team-oriented environment. Preferred Qualifications: Experience with hardware design, testing, data acquisition, and analysis. Familiarity with missile systems, defense technology, or aerospace components. Strong interest in working in a startup environment with high-impact projects. Why Castelion? At Castelion, you'll be part of a mission-driven company where every project matters. Our interns don't just observe - they contribute meaningfully to the success of our programs. This is a unique opportunity to work at the cutting edge of aerospace engineering while developing the skills and experience that will help you grow into a future leader in the field. 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. 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, the applicant must be a (i) U.S. citizen or national, (ii) U.S. lawful, permanent resident (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. This internship is paid at an hourly rate of $30 per hour. Compensation may vary based on experience and education level. For non-local interns, housing or relocation stipends may be available to help offset temporary living expenses.