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.

Summer 2027 Mechanical Engineering Internships

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.

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 [email protected]. 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.

Castelion

Mechanical Engineer Intern

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Castelion

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