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About the job Embedded Software Engineer Intern - Summer 2026 (Avionics)
About Castelion
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.
Embedded Software Engineer Intern - Summer 2026 (Avionics)
Castelion is seeking motivated and talented Embedded Software Engineering interns for Summer 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 wont 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.

Why Castelion
At Castelion, you'll be part of a mission-driven company where every project matters. Our interns don't just observe. They contribute meaningfully to the success of our programs. This is a unique opportunity to work at the cutting edge of aerospace engineering while developing the skills and experience that will help you grow into a future leader in the field.
You'll leave with

• Direct experience working on software that flies

• Real-world debugging and test experience on integrated hardware

• Mentorship from engineers who have shipped systems under tight timelines

• The chance to help shape the future of defense manufacturing

Leadership Qualities

• Bias to Action and Creative Problem Solving. Desire and experience questioning assumptions in ways that lead to break through ideas that are ultimately implemented. Successfully bring in applicable processes/concepts/materials from other industries to achieve efficiency gains. The 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.

ITAR Requirements

• To conform to U.S. Government export regulations, the 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.
This internship is paid at an hourly rate of $30 per hour. Compensation may vary based on experience and education level. For non-local interns, housing or relocation stipends may be available to help offset temporary living expenses.