Senior Mechanical Engineer; Propulsion

Propulsion Mechanical Engineer

Apex is seeking a Propulsion Mechanical Engineer to own mechanical designs for our spacecraft propulsion systems. You will drive the design, analysis, and qualification of propulsion hardware that must perform reliably through launch environments and long-duration on-orbit operations. This role spans mechanical design, fluid system development, thermal interfaces, and flight hardware qualification, with end-to-end ownership from early concept through flight readiness and operational performance.

You will work closely with propulsion, thermal, avionics, and systems engineering teams to deliver robust, repeatable propulsion hardware designed for production spacecraft.

• Own the mechanical design of propulsion system hardware and its integration into propulsion modules, including thrusters, PPUs, manifolds, flow control hardware, high-pressure propellant lines, and tanks.
• Perform analysis and testing to satisfy propulsion subsystem requirements across performance, safety, and environmental constraints.
• Design propulsion module structures and housings, plasma-facing components, mounts, thermal straps, and mechanical interfaces.
• Perform structural and vibration analyses to support launch loads, thermal cycling, and long-duration on-orbit operation.
• Generate and maintain CAD models, drawings, and GD&T for flight hardware.
• Support manufacturing, assembly, and integration of propulsion and fluid hardware.
• Plan and execute propulsion hardware testing, including vacuum testing, performance testing, leak testing, proof pressure testing, vibration, and thermal vacuum qualification.
• Diagnose test anomalies related to propulsion system testing and drive corrective action and design iteration.
• Partner with systems engineering on requirements, margins, and subsystem interfaces.
• Support launch campaigns, on-orbit performance evaluation, and anomaly resolution.
• Contribute to failure analysis and continuous design improvements to support future builds and scalable production.

• Bachelor's degree in Mechanical Engineering, Aerospace Engineering, or a related field.
• 8+ years of experience delivering mechanical and/or fluid system hardware.
• Strong foundation in fluid mechanics, including compressible and/or rarefied gas flow, pressure drop/flow control, and cleanliness/contamination control.
• Experience designing and developing pressurized fluid systems.
• Proficiency with CAD tools (NX preferred).
• Comfortable owning hardware from concept through qualification and flight.
• Strong interpersonal skills and ability to work effectively across multidisciplinary teams.

• Experience with electric propulsion systems (Hall thrusters, ion thrusters, or related EP).
• Experience with spacecraft propellant feed systems and/or xenon (or alternative EP propellants).
• Familiarity with propulsion testing in vacuum facilities and vacuum system gas behavior.
• Prior flight hardware experience.

Apex believes in creating a work environment that you look forward to embracing every day. Our employees love working at Apex, and we want you to love it too. We're a fast-growing startup that has raised more than $500M in funding, and we invest heavily in our people from day one.

• Shared upside: Receive equity in Apex, letting you benefit from the work you create
• Best-in-class healthcare: 100% company-paid medical, dental, and vision for you and your dependents, plus $100k life insurance at no cost
• Comprehensive PTO package: To reset and recharge - starting at 15 days vacation, growing to 20+ days annually, plus 10 paid holidays
• Competitive 401(k) plan: With generous matching - 100% match on first 3%, 50% on next 2%
• 8 weeks paid parental leave: Plus childcare reimbursement up to $350/day for work-related travel
• Daily catered lunch and unlimited snacks: To keep you fueled throughout the day
• Vibrant community: Monthly office socials, pickleball tournaments, run club, and gatherings for you and your family
• Your dream desk setup: And all the tools you need to be your most productive self
• World-class Playa Vista office: With the benefit of in-person…