Senior Mechanical Engineer

Join to apply for the Senior Mechanical Engineer role at Marathon Fusion

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Join to apply for the Senior Mechanical Engineer role at Marathon Fusion

Off the back of our recent publication, we are hiring for technical roles across a wide variety of disciplines and backgrounds. Due to an unusually high level of interest during this time, we may be slow to respond.

Since our founding in 2023, we’ve developed fuel cycle technologies to deliver fusion energy more quickly with better economics. Marathon Fusion was founded by Adam Rutkowski, previously a Propulsion Engineer at Space

X and PhD candidate in Plasma Physics at Princeton University, and Kyle Schiller, previously a Fellow in science policy at Schmidt Futures. We believed then, and now more than ever, that fusion is humanity’s best pathway to abundant, clean and reliable energy.

We’ve secured over $10m in funding from the US Department of Energy and leading investors including 1517 Fund and Strong Atomics. We have letters of intent from leading fusion companies including Helion Energy, Commonwealth Fusion Systems, and Thea Energy.

We’ve built plasma centrifuges for isotope separation and superpermeable pumps for rapid fuel recycling in fusion power plants. We’re on a quest to commercialize alchemy, accelerate the deployment of fusion energy, and open a new frontier in scientific discovery.

We are a startup environment characterized by a need for focus, adaptability and prioritization in a shifting landscape. Thriving in this environment requires excellent proactive communication across roles and backgrounds, the ability to build and maintain trust between team members, and the willingness to learn and develop new skills on the job. We place particularly high weight on each team member’s ability to be self‑directed.

As a Senior Mechanical Engineer, you’ll work closely with mechanical engineers, physicists, and technicians to prototype, test, and deploy solutions in the pursuit of advancing the development of the fusion fuel cycle and stable isotope production. We are seeking an engineer with hands‑on experience designing and testing electromechanical systems.

This role requires a blend of practical engineering skills and systems level thinking. You will play a pivotal role in the development and iteration of a first‑of‑kind isotope separation device through system and component design and hands‑on prototyping and testing.

• Lead the iterative design and improvement of an isotope separation system, driving toward robust, scalable deployment
• Prototype, test, and troubleshoot components and integrated systems in close collaboration with other engineers, physicists and technicians
• Develop first‑principles understanding of key physical processes and guide improvements based on experimental data and literature
• Document experimental results and decisions clearly to inform design iterations and process development
• Mentor and support junior engineers, fostering technical growth and strong engineering judgment on the team

• B.S. or higher in Mechanical Engineering or related field
• 5+ years of hands‑on experience in design, prototyping, and testing of electromechanical systems
• Experience as a design lead or program lead on a team of Mechanical Engineers
• Demonstrated experience with high vacuum systems
• Familiarity with high voltage equipment and safety practices
• Strong experimental skills and ability to draw insights from physical systems
• Proficiency in mechanical design, including CAD, GD&T, and DFM best practices
• Capacity to learn new technical subjects quickly, collaborate cross‑functionally, and consider problems from inter‑disciplinary perspectives
• Ability to thrive in ambiguity, drive projects forward, take ownership and flag when results are not moving the needle
• Excellent written and oral communication

• Experience instrumenting and collecting data off your own systems
• Experience working with high voltage or plasma systems
• Proven experience mentoring junior engineers
• Process development experience in…