Mixing Engineer Jobs in California (NOW HIRING)

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.

Castelion is seeking a Senior Manufacturing Engineer to own the propellant mixing and casting value stream for our solid rocket motor programs. In this hands‑on technical leadership role, you will develop, qualify, and scale safe, repeatable, and rate‑capable processes for the formulation, mixing, vacuum casting, and curing of energetic materials. You will drive aggressive improvements in yield, cycle time, cost per pound, and safety while supporting a rapidly growing production rate for mission‑critical defense systems.

• Process Development and Ownership. Own all technical aspects of propellant mixing and casting operations. Develop and qualify new propellant formulations, mixing procedures, vacuum‑casting processes, and cure cycles. Establish process windows, control plans, and critical‑to‑quality parameters that deliver consistent grain geometry, void‑free castings, and predictable ballistic performance.
• Continuous Improvement and Yield Enhancement. Lead root‑cause investigation and corrective‑action efforts for casting defects (voids, cracks, unbonded regions, inclusions). Implement advanced process monitoring (real‑time rheology, vacuum sensing, thermal imaging) and in‑situ inspection techniques to achieve first‑pass yield >95%. Drive labor‑hour and material‑waste reduction through fixture design, batch‑size optimization, automation of material handling, and de‑aeration steps.
• Scale‑up and Rate Readiness. Plan and execute the transition from development‑scale mixing to full‑rate production. Specify, procure, and commission high‑capacity vertical/horizontal mixers, casting pits, vacuum systems, and automated propellant transfer equipment. Develop facility layouts and material‑flow designs that support simultaneous multi‑program production while maintaining explosive quantity‑distance compliance.
• Safety and Regulatory Leadership. Author and maintain hazard analyses, SOPs, and explosive safety submissions specific to propellant mixing and casting. Lead process hazard analyses (PHA) and ensure all equipment and procedures incorporate quantity‑distance, ESD, and personnel exposure limits. Champion rigorous change control for any formulation or process modification.
• Cross‑Functional Collaboration and NPI Support. Serve as the primary propellant subject‑matter expert to Design Engineering during grain‑design trades and liner/insulator compatibility reviews. Support new product introduction by generating PFMEAs, performing qualification casting runs, and establishing non‑destructive evaluation criteria (ultrasonic, X‑ray CT) for cast grains. Interface directly with Quality, EHS, and customers on non‑conformances and anomaly resolution.
• Tooling and Automation. Design or specify reusable casting mandrels, vacuum systems, transfer pots, and automated de‑molding systems. Integrate digital tools (MES recipes, real‑time data acquisition, predictive viscosity modeling) to reduce operator dependency and enable 24/7 unattended curing.

• Bachelor's degree in Chemical Engineering, Mechanical Engineering, Aerospace Engineering, or related field.
• Minimum 7 years of direct hands‑on experience in process‑sensitive manufacturing fields, ideally within the energetics space.

• Track record of scaling composite propellant production.
• Hands‑on experience specifically in propellant mixing, vacuum casting, and case‑bonded grain production or equivalent.
• Deep knowledge of propellant formulations, isocyanate curing chemistry, pot‑life management, rheological modeling, and void‑prediction/mitigation techniques.
• Hands‑on experience qualifying new propellant formulations and casting processes for DoD programs (tactical, missile defense, strategic, or space launch).
• Familiarity with advanced NDE methods for cast energetics (phased‑array ultrasound, digital radiography, CT scanning).
• Prior work in facilities holding ATF licenses and DoD explosive safety approvals.
• Strong aptitude for scripting/automation (Python, LabVIEW) and integrating sensors into legacy energetics equipment.
• Ability to thrive in a fast‑paced startup environment with aggressive schedules and evolving requirements.

• Bias to Action and Creative Problem Solving. Desire and experience questioning assumptions in ways that lead to breakthrough ideas that are ultimately implemented. Successfully bring in applicable processes, concepts, or 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.

• To conform to U.S. Government export regulations, 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.

All employees are granted long‑term stock incentives as part of their employment at Castelion. All employees receive access to comprehensive medical, vision, and dental insurance, and the company offers four weeks of paid time off per year.