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. HITL Test Infrastructure Engineer As a HITL Test Infrastructure Engineer, you will architect, develop, and own Castelion's Hardware-in-the-Loop (HITL) test infrastructure used to verify embedded software and firmware running on flight-critical hardware. Your systems will enable developers and automated CI/CD pipelines to reserve physical hardware, deploy software and firmware, execute automated tests, and rapidly validate system performance using production-representative hardware. You'll work across software, firmware, avionics, FPGA, electrical, and systems engineering teams to build scalable, resilient, and highly automated test environments supporting microcontrollers, FPGAs, GPUs, and custom electronics. Your work will significantly improve development velocity and software quality by providing engineers with fast, reliable feedback before hardware reaches the vehicle. At Castelion, engineers own their systems from concept through production. You'll design infrastructure that is robust, maintainable, intuitive to use, and capable of scaling alongside our rapidly growing engineering organization.
Responsibilities Design, develop, and own Castelion's Hardware-in-the-Loop (HITL) test infrastructure for embedded software and firmware verification. Build scalable HITL test stations capable of supporting microcontrollers, FPGAs, GPUs, and custom compute hardware with specialized power and interface
requirements. Develop automated test frameworks that verify software loading, boot sequences, runtime performance, functional behavior, and system
requirements. Integrate HITL systems into Kubernetes and CI/CD workflows, enabling developers and automated verification pipelines to reserve hardware, flash devices, execute tests, and review results. Develop Python-based test software, automation tools, and infrastructure to maximize test coverage and engineering productivity. Design automated test execution strategies for code commits, pull requests, nightly builds, release candidates, and other development milestones. Build reliable hardware reservation, scheduling, and resource management capabilities that maximize lab utilization. Partner closely with software, firmware, FPGA, avionics, electrical, and systems engineers to define verification
requirements and expand automated test coverage. Debug complex issues spanning hardware, firmware, software, networking, and infrastructure. Continuously improve the reliability, scalability, uptime, automation, and user experience of Castelion's HITL infrastructure. Support board bring-up, hardware integration, lab automation, and prototype testing activities as new hardware platforms are introduced. Establish best practices for automated verification, hardware management, and continuous integration across engineering teams. Basic
Qualifications Bachelor's degree in Computer Engineering, Electrical Engineering, Computer Science, Software Engineering, or a related technical discipline, or equivalent practical experience. Experience developing software using Python. Experience building automated test frameworks using tools such as pytest, Robot Framework, or similar. Familiarity with embedded software and firmware development workflows, including flashing, booting, debugging, and runtime validation. Experience working with serial, JTAG, SWD, or similar hardware debug interfaces. Basic understanding of embedded hardware and the ability to read electrical schematics. Experience working in Linux development environments. Basic understanding of Kubernetes, containerized infrastructure, or modern CI/CD systems. Ability to troubleshoot issues across hardware, firmware, software, and infrastructure boundaries. Comfortable working in a laboratory environment with custom electronics, instrumentation, power supplies, and prototype hardware. Preferred Skills and Experience Experience developing Hardware-in-the-Loop (HITL) or automated hardware test systems. Experience integrating hardware validation into CI/CD pipelines. Experience with microcontrollers, FPGAs, GPUs, SoCs, or custom embedded compute platforms. Experience with board bring-up, lab automation, instrument control, power sequencing, or custom power delivery systems. Familiarity with FPGA development workflows, including VHDL, Verilog, or SystemVerilog. Experience reading FPGA code to understand interfaces, expected behavior, and verification
requirements. Experience with Git-based software development workflows. Experience building hardware reservation, orchestration, or resource scheduling systems. Experience with networking, distributed systems, or Kubernetes-based infrastructure. Experience developing scalable engineering infrastructure supporting multiple development teams. 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.
About Castelion
Castelion is a modern defense production company building long-range hypersonic strike systems to address a critical national security gap. Founded in 2021, Castelion was created in response to the recognized need for the United States to rapidly develop hypersonic capabilities to remain competitive with near-peer adversaries and deter future conflicts.
The company operates under the philosophy of "Peace through Deterrence" — building the weapons systems that ensure conflicts never need to happen. Castelion is one of the few companies in the hypersonics space that has moved beyond concepts to actual production deliverables, with government contracts across multiple branches of the military and a $23M+ Navy order for 50 units in calendar year 2027.
Backed by over $469M in funding from top-tier investors including Andreessen Horowitz, Lightspeed Venture Partners, and General Catalyst, Castelion is scaling rapidly. The company is building what it anticipates will become the preeminent hypersonics campus in the country — including a $150M, 1,000-acre solid rocket motor manufacturing facility in Rio Rancho, New Mexico, alongside its headquarters in Torrance, California.
Castelion's culture is defined by technical excellence, ownership, and velocity. Engineers own meaningful subsystems on the vehicle and are responsible for driving their success. The company follows a responsible engineering model inspired by SpaceX, where individuals choose the highest-value work and are empowered to cultivate resources and partnerships to deliver results. The engineering bar is exceptionally high — attracting elite talent who want to be surrounded by other elite talent.
