Senior Flight Software Engineer (TS Cleared) with Security Clearance

As a member of the Flight Software team, you will design, develop, and own the software that brings our spacecraft to life. You will tackle the hardest problems in autonomous systems and build robust software that enables reliable spacecraft operation 24/7, across every phase of a mission. You will work closely with our mission operations, GNC, and hardware teams to architect new systems, prototype ideas, and turn them into mission-critical software that ultimately flies. Experience in the space industry is not necessary to thrive at Apex.

Instead, we are looking for motivated engineers who enjoy solving complex problems, balance technical rigor with practicality, and thrive in a dynamic, fast-paced environment. The Flight Software team is composed of three interconnected teams: high-level application software, operating system software, and embedded software. There is significant collaboration and crossover across these teams. Responsibilities

• Design, develop, and own mission-critical software for satellite systems throughout the full software lifecycle, from initial architecture and development through deployment and operations.
• Develop rapid, iterative software to support bench and development testing, as well as robust, rigorously reviewed and validated software delivered to manufacturing and flight systems.
• Plan and execute unit, integration, and system-level testing of satellite components, diagnosing and resolving defects to ensure software quality, reliability, and performance.
• Collaborate cross-functionally with systems, hardware, test, and operations teams to establish product requirements, define technical roadmaps, and drive successful execution.
• Support spacecraft commissioning during launch and early operations, troubleshooting software and ensuring critical flight systems remain functional and reliable throughout critical mission activities. Requirements
• U.S. Citizenship (must possess the ability to access export-controlled data)
• Active Top Secret or Top Secret/SCI clearance required; ability to obtain and maintain access to additional programs as needed.
• 8+ years of total flight software experience
• Bachelor’s degree in CS, EE, or equivalent
• Strong proficiency in programming languages such as C++, Python, or Rust Preferred
• Experience developing, testing, deploying, and troubleshooting mission-critical satellite software from prototyping through flight operations.
• Experience with real-time software on distributed hardware platforms across multiple satellite products.
• Knowledge of embedded and real-time operating systems (e.g., Embedded Linux, Yocto, Buildroot, FreeRTOS, VxWorks).
• Experience writing and debugging low-level device drivers for hardware interfaces (e.g., SPI, I²C, UART, Ethernet, CAN, SpaceWire).
• Familiarity with satellite communication standards and protocols (e.g., CCSDS, ECSS).
• Familiarity with networking and secure communications (e.g., TCP/IP, UDP, TLS), data serialization (e.g., Protobuf, JSON, MessagePack), and encryption (e.g., AES, RSA).
• Experience translating requirements into technical solutions, defining technical roadmaps, and coordinating with cross-functional engineering teams to support project execution.
• Experience supporting spacecraft commissioning during launch and early operations.
• Experience with version control, configuration management, automated testing, and CI/CD pipelines for software build, deployment, and release.

Pay Range

Senior: $225K+ (Base + Equity)
Staff: $300k+ (Base + Equity)