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, ownership, and excellence are decisive advantages - and we're building a world-class team to turn bold ideas into real capability. 

This is a rare opportunity to join at an early stage, where you'll have significant ownership, collaborate with exceptional teammates, and make a direct, measurable impact on our mission and the future of the company - regardless of your function.  

 

Embedded Software Engineer Intern - Fall 2026

Castelion is seeking motivated and talented Embedded Software Engineering interns for Fall 2026. You'll help create the software that drives and simulates our missile systems, from low-level firmware on microcontrollers to high-level integration and testing tools. You'll work alongside experienced embedded, hardware, and flight systems engineers to design, implement, test, and debug real systems in the loop. 

You won't be writing throwaway code; your contributions will directly support our rapid prototyping and real-world tests.

 

Responsibilities

• Develop, test, and debug low-level firmware for embedded systems and flight hardware

• Write and integrate device drivers for sensors, actuators, and missile subsystems

• Bring up new hardware, test boards, and debug at the intersection of electrical and software layers

• Collaborate cross-functionally with hardware, GNC, and flight test teams to ensure robust integration

• Participate in design reviews, hardware-in-the-loop tests, and on-the-bench bring-up and validation

• Document your work clearly and share learnings to improve team knowledge and future designs

Basic Qualifications

• Currently pursuing a BS or MS in Computer Engineering, Electrical Engineering, Computer Science, or a related technical field

• Rising junior, senior, or graduate student at the time of the internship

• Strong C/C++ programming skills for embedded systems

• Experience with microcontrollers or SoCs (ARM, AVR, MSP430, PIC, etc.)

• Familiarity with developing in bare-metal or RTOS environments

• Understanding of board bring-up and debugging fundamentals

• Some familiarity with common protocols: SPI, I2C, CAN, UART, Ethernet, etc.

• U.S. Person status required (due to ITAR regulations)

Preferred Skills and Experience

• Experience integrating analog/digital hardware with firmware

• Familiarity with missile systems, defense technology, or aerospace components.
• Strong interest in working in a startup environment with high-impact projects.

Castelion offers a generous benefits package. Please refer to the bottom of our Careers page for more details.  

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. 

Additional Eligibility Requirements 

This position may require access to classified information or restricted U.S. Government sites, systems, or information, as determined by the Company and/or applicable U.S. Government requirements. If the position is so designated, your employment in the role may be contingent upon your ability to obtain and maintain the required U.S. Government security clearance or other government authorization, and to satisfy any citizenship or other eligibility requirements imposed by applicable law, regulation, executive order, or government contract requirements. You will be notified if and when such requirements apply. 

Affirmative Action/EEO Statement 

Castelion is an Equal Opportunity Employer. We are committed to providing equal employment opportunities to all applicants and employees without regard to race, color, religion, sex, sexual orientation, gender identity, national origin, age, disability, genetic information, protected veteran status, or any other characteristic protected by applicable federal, state, or local law. 

Castelion is committed to providing reasonable accommodations to qualified individuals with disabilities throughout the application and hiring process. If you require a reasonable accommodation to complete an application, participate in the interview process, or otherwise participate in the hiring process, please contact hr@castelion.com. Requests for accommodation will be considered on an individual basis and handled in accordance with applicable law. 

Castelion is committed to fostering a workplace where employment decisions are based on qualifications, business needs, and the ability to perform the essential functions of the role, with or without reasonable accommodation. 

EAR/ITAR Requirements 

This position requires access to export-controlled information, and as such, employment (or hiring of a contractor) is contingent upon the candidate’s ability to access all applicable export-controlled information without additional export licensing being required by the Bureau of Industry and Security and/or the Directorate of Defense Trade Controls.