Senior Mechanical Design Engineer (Structures & Thermal Protection Integration)

About the role

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 and technical excellence are decisive advantages - and we are building a team that can deliver real capability, not just concepts. This is a rare opportunity to join at an early stage, where your work will directly shape critical systems, influence major technical decisions, and have immediate, real-world impact. We are seeking a Senior Mechanical Design Engineer to design and deliver critical flight vehicle structures for Castelion's long-range hypersonic strike vehicles. This role is focused on structural systems that interface with and enable the thermal protection system (TPS), including separating nose tip architectures and other high-temperature structural components. You will work hands-on with multidisciplinary engineering teams to design, analyze, build, and validate flight-critical structures in a fast-paced, hardware-driven environment.

Responsibilities

• Design and develop flight vehicle structures, including separating nose tip systems and other components critical to thermal protection system (TPS) performance
• Lead the architecture and detailed design of high-temperature structural assemblies, including joints, interfaces, and load paths across TPS and primary structure
• Perform structural and thermal analyses to ensure performance and reliability under extreme aerothermal, pressure, and dynamic environments
• Work closely with materials, TPS, aerothermal, GNC, and manufacturing teams to ensure seamless integration of structures with vehicle systems
• Develop and analyze separation mechanisms and interfaces, ensuring reliable and repeatable operation under flight conditions
• Conduct tolerance analysis and assess thermal expansion, material compatibility, and interface behavior at elevated temperatures
• Support prototyping, assembly, and hardware bring-up, including troubleshooting and root cause analysis of structural and interface performance issues
• Define and execute qualification and environmental test plans, including thermal, vibration, and shock testing
• Optimize designs for mass, thermal performance, structural integrity, and manufacturability
• Mentor junior engineers and contribute to best practices in high-temperature structural design
• Partner closely with program leadership to make technical trades aligned with mission success

Requirements

• Bachelor's, Master's, or PhD in Mechanical Engineering or related field
• 5+ years of experience in structural design and analysis for aerospace or high-performance systems
• Strong background in high-temperature structures and materials, particularly in TPS-adjacent or aerothermal environments
• Experience designing separation systems, joints, and structural interfaces for flight hardware
• Proficiency in CAD and analysis tools (e.g., NX, SolidWorks, ANSYS, or equivalent)
• Experience with structural and thermal analysis, including thermal-structural coupling and tolerance stack-up
• Familiarity with materials used in high-temperature environments (e.g., ceramics, carbon-carbon, refractory metals, or similar)
• Experience with hardware build, test, and troubleshooting in a lab or flight hardware environment
• Strong problem-solving mindset, thriving in a fast-paced, hardware-rich, high flight cadence environment
• Ability to obtain and maintain a U.S. government–issued security clearance required
• U.S. citizenship required

Benefits

• Meaningful long-term equity for all full-time employees, sharing in the company's significant growth trajectory
• Four (4) weeks of paid time off
• Ten (10) company-paid holidays
• Comprehensive health benefits – 100% employee-covered medical, strong dependent coverage, dental and vision plans
• Paid parental leave to support growing families
• $100 monthly fitness stipend to promote health and performance
• Onsite EV charging for convenience
• Catered meals and company-covered food during high-demand periods
• Fully stocked kitchen to stay fueled throughout the day