Mechanical Engineering Intern (Summer 2026+)

Off the back of our recent publication, we are hiring for technical roles across a wide variety of disciplines and backgrounds. We are currently experiencing an unusually high volume of interest. We appreciate your patience as we work to review all applications.

Please review these points carefully before applying:

• This application is exclusively for the Mechanical Engineering track.

• We provide both Internship and Co-op placements through this single posting.

• We offer specialized tracks in Engineering Physics and Physics Modelling under separate applications.

CRITICAL: Please use your best judgment to select the single track that best fits your background. Candidates who apply for multiple internships will not be considered.

About Marathon Fusion

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 SpaceX 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, 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.

Culture at Marathon Fusion

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.

Technical Roles at Marathon Fusion

We are primarily interested in interns who are:

• Studying physics, but have meaningful hands on experience including in fabrication, mechanical engineering, test engineering, vacuum systems operation, or similar.

• Studying mechanical engineering, but have had meaningful exposure to physics through coursework, internships, projects or personal study.

• Studying a combination of both in an engineering physics program, double major or similar.

• Studying an engineering field or other technical field and have exceptional work-ethic, eagerness to learn, and autonomy.

Mechanical Engineering Intern Role

This track focuses heavily on the design, prototyping, and testing of physical hardware components used in extreme scientific environments. Successful candidates will be responsible for creating robust, manufacturable mechanical systems that directly enable our core technology.

Core Responsibilities and Focus Areas

• Design and Analysis: CAD modeling, structural analysis, component selection, and integrated mechanical system design.

• Testing and Validation: Developing and executing tests, including thermal management solutions, for physical hardware components.

• Prototyping: Taking designs from concept through to prototype, ensuring manufacturability and material compatibility.

Example Projects

Interns and Co-ops in this role have previously been involved in:

• Designing a mercury plasma centrifuge (complete with CAD models and material compatibility considerations).

• Leading the design and assembly phases of complex co-op projects like the plasma chemistry centrifuge.

Preferred (But Not Required) Experience

We don't expect, but would be particularly excited about any candidates with experience in the following: plasma physics, vacuum systems, mercury handling, lithium handling, isotope separation systems, fabrication for scientific applications, nuclear physics.

For all roles, importan