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.

Role Overview

As a Mechanical Engineer (Test & Tooling), you will own the design, development, and deployment of mechanical systems that enable rapid, high-fidelity testing and scalable production of avionics and integrated weapon subsystems.

You will lead the creation of environmental test fixtures (vibration, thermal, HALT/HASS), hardware-in-the-loop (HITL) and vehicle-in-the-loop (VITL) support hardware, production test equipment, and production tooling that accelerates build and integration. You will partner closely with cross-functional design, test, and manufacturing engineering teams to ensure hardware can be validated quickly, reliably, and at large scale for production.

This role requires strong mechanical design fundamentals, deep understanding of test environments and failure modes, and the ability to translate ambiguous test objectives into robust, repeatable physical systems. You will be expected to execute with high ownership, iterate quickly, and continuously improve Castelion's test infrastructure and tooling ecosystem.

Responsibilities

• Own end-to-end design of mechanical fixtures for environmental testing, including vibration, shock, and thermal cycling.
• Design and develop HALT/HASS profiles and the associated fixtures to expose product weaknesses and validate reliability margins.
• Create test fixtures for avionics systems, ensuring accurate mechanical, electrical, and environmental interfaces.
• Create test racks & interface chassis containing electronics & test equipment
• Design and optimize test and production fixtures and build tooling to improve assembly efficiency, repeatability, and throughput.
• Translate test requirements into robust fixture designs that ensure proper load paths, boundary conditions, and instrumentation access.
• Perform structural, thermal, and tolerance analyses to validate fixture performance under test conditions.
• Select materials, fasteners, and manufacturing processes appropriate for dynamic, thermal, and high-reliability environments.
• Partner with test engineers to instrument fixtures (strain, acceleration, temperature) and validate correlation to expected conditions.
• Drive design for manufacturability (DFM) and design for assembly (DFA) for all fixtures and tooling.
• Interface directly with machine shops, vendors, and internal manufacturing teams to fabricate and iterate on designs quickly.
• Support test execution, troubleshoot failures, and rapidly iterate fixture designs based on test outcomes.
• Develop and maintain drawings, CAD models, and documentation for all fixtures and tooling.
• Contribute to internal standards and best practices for test infrastructure and mechanical design.

Basic Qualifications

• 2–5+ years of experience in mechanical design, preferably in test, tooling, or hardware development environments.
• Strong proficiency with CAD tools (NX, SolidWorks, or equivalent).
• Proven experience designing fixtures or tooling for mechanical, thermal, or environmental testing.
• Solid understanding of structural mechanics, thermal behavior, and material properties under dynamic loading.
• Experience designing for vibration and shock environments, including bolted joints and interface design.
• Familiarity with tolerance analysis and GD&T.
• Experience working with machine shops and external fabrication vendors.
• Strong problem-solving skills and ability to iterate quickly in fast-paced environments.
• High ownership mindset with the ability to drive designs from concept through deployment.
• Ability to work effectively across cross-functional engineering teams.

Preferred Skills and Experience

• Experience in aerospace, missile systems, spaceflight, defense, or other high-reliability hardware environments.
• Hands-on experience with:
• Vibration and shock testing (random vibe, sine burst, pyroshock)
• Thermal and thermal vacuum testing
• HALT/HASS methodologies and reliability engineering
• Experience designing fixtures for HITL or VITL systems.
• Familiarity with instrumentation (accelerometers, strain gauges, thermocouples) and data acquisition systems.
• Experience with FEA tools for structural and thermal analysis (e.g., ANSYS, Nastran, Abaqus).
• Experience using and tailoring relevant environmental standards (MIL-STD-810, MIL-STD-1540).
• Experience optimizing production tooling and assembly workflows.
• Ability to rapidly prototype (CNC, additive manufacturing, sheet metal).
• Experience supporting hardware through environmental testing and qualification campaigns.
• Demonstrated ability to mentor engineers and elevate team design quality.

Additional Requirements

• Willingness to support extended hours or weekend work during critical integration, test, and flight milestones.

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.

Benefits And Perks

All full-time employees are granted meaningful long-term equity, sharing in the company's significant growth trajectory. We offer four (4) weeks of paid time off, ten (10) company-paid holidays, and comprehensive health benefits - including 100% employee-covered medical and strong dependent coverage, along with dental and vision plans. We also provide paid parental leave to support growing families, a $100 monthly fitness stipend to promote health and performance, and onsite EV charging for convenience. In addition, employees enjoy perks like catered meals, company-covered food during high-demand periods, and a fully stocked kitchen to stay fueled throughout the day.

While this position does not currently require a U.S government-issued security clearance, it may in the near future. Therefore, the ability to obtain and maintain a U.S. government–issued security clearance is required. U.S. citizenship is required, as only U.S. citizens are eligible for a security clearance.

Affirmative Action/EEO Statement
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.