Embedded Software Engineer Intern - Fall 2026

About the role

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 motivated and talented Embedded Software Engineering interns for Fall 2025. 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.

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, and the chance to help shape the future of defense manufacturing.

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

Requirements

• 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)

Qualifications

• 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
• Leadership qualities: bias to action and creative problem solving; desire to question assumptions; ability to bring in applicable processes/concepts/materials from other industries; ability to personally resolve minor issues without significant support; high commitment and initiative; ability to work in a fast