Responsibilities Design and develop ACS hardware, including propellant tanks, valves, thrusters, and associated fluid system assembliesLead the architecture and detailed design of pressure vessels, fluid lines, mounts, and integrated ACS packaging within the vehiclePerform structural, thermal, and fluid analyses to ensure performance and reliability under extreme pressure, temperature, and dynamic environmentsWork closely with propulsion, GNC, avionics, and structures teams to ensure seamless integration of ACS systems with vehicle architectureConduct tolerance analysis, sealing strategy development, and leak-tightness assessments for high-pressure systemsSupport prototyping, assembly, and hardware bring-up, including troubleshooting and root cause analysis of system performance issuesDefine and execute qualification and environmental test plans, including pressure, vibration, thermal, and shock testingOptimize designs for mass, reliability, manufacturability, and ease of integrationMentor junior engineers and contribute to best practices in mechanical and fluid system designPartner closely with program leadership to make technical trades aligned with mission successBasic Qualifications Bachelor's, Master's, or PhD in Mechanical Engineering or related field5+ years of experience in mechanical design for aerospace or high-performance fluid/propulsion systemsStrong background in pressure vessel design, fluid systems, and high-pressure component integrationExperience designing tanks, valves, thrusters, or similar propulsion or ACS hardwareFamiliarity with sealing methods, leak detection, and cleanliness requirements for high-reliability fluid systemsProficiency in CAD and analysis tools (e.g., NX, SolidWorks, ANSYS, or equivalent)Experience with structural analysis, thermal analysis, and tolerance stack-up analysisFamiliarity with high-temperature materials and operation in extreme environmentsExperience with hardware build, test, and troubleshooting in a lab or flight hardware environmentStrong problem-solving mindset, thriving in a fast-paced, hardware-rich, high flight cadence environmentOther 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. Senior Mechanical Design Engineer (ACS Systems) We are seeking a Senior Mechanical Design Engineer to design and deliver attitude control system (ACS) hardware for Castelion's long-range hypersonic strike vehicles.