Principal Thermal Control System (TCS) Design Engineer

K2 is building the largest and highest-power satellites ever flown, unlocking performance levels previously out of reach across every orbit. Backed by $450M from leading investors including Altimeter Capital, Redpoint Ventures, T. Rowe Price, Lightspeed Venture Partners, Alpine Space Ventures, and others – with an additional $500M in signed contracts across commercial and US government customers – we’re mass-producing the highest-power satellite platforms ever built for missions from LEO to deep space. The rise of heavy-lift launch vehicles is shifting the industry from an era of mass constraint to one of mass abundance, and we believe this new era demands a fundamentally different class of spacecraft. Engineered to survive the harshest radiation environments and to fully capitalize on today’s and tomorrow’s massive rockets, K2 satellites deliver unmatched capability at constellation scale and across multiple orbits. With multiple launches planned through 2026 and 2027, we're Building Bigger to develop the solar system and become a Kardashev Type II (K2) civilization. If you are a motivated individual who thrives in a fast-paced environment and you're excited about contributing to the success of a groundbreaking Series C space startup, we’d love for you to apply. The Role You will own the end-to-end architecture, development, and lifecycle success of spacecraft thermal control systems (TCS) across both RD and production programs. As the technical authority, you will define system-level thermal strategies and lead the design, integration, and verification of advanced active and passive thermal control solutions, including pump-driven fluid loops, heat pipes, and associated ground support infrastructure (test systems, diagnostics, instrumentation, and software tools). You will drive cross-functional alignment across mechanical, electrical, and manufacturing teams, ensuring thermal system designs are robust, scalable, and production-ready. This includes establishing design standards, verification methodologies, and qualification frameworks for high-reliability components for space environments. This role requires deep expertise in pressurized fluid systems (valves, pumps, accumulators, heat exchangers), thermo-mechanical instrumentation (temperature, pressure, and flow sensing), integrated avionics, and structural interfaces. You will lead system-level trade studies, risk assessments, and failure investigations, setting the technical direction for thermal performance and reliability. From early concept through production ramp, you will partner with design and manufacturing teams to ensure design for manufacturability and testability, define build and integration flows, and oversee the successful transition from prototype to high-rate production. Responsibilities Lead the design of active and passive thermal control systems using basic heat transfer and mechanical equations to size lines, pumps, accumulators, cold plates etc. Collaborate with lead engineers on design and iterate on TCS architecture Lead procurement of long-lead items and actively seek opportunities to shorten timeline Define the roadmap for future improvement of active TCS Planning and development of thermal cycle and thermal-vacuum testing campaigns Design and develop ment of heater and cooling systems including control architecture Setup, commission, and maintain state-of-the-art test stands and instrumentation Develop data acquisition systems for active and passive thermal control systems Perform tests on novel pump fluid l oop including feed systems, power electronics, and hardware-in-the-loop Develop testing and control scripts to conduct safe and reliable test campaigns of pump fluid loop and individual components Create formal documentation for development and production: test procedures, test reports, and standard operating procedures Troubleshoot electrical and mechanical test setups and hardware Document, compile, analy ... (truncated, view full listing at source)