About Us At Antares, our long-term mission is to make clean energy abundant from Earth to the Asteroid Belt. We’re fueled by the belief that advanced nuclear energy can strengthen our military, solve the climate crisis, elevate global living standards, and expand humanity's presence in outer space. To achieve our mission, we’re building mass-producible, inherently safe, deployable microreactors that can be used terrestrially, underwater, and in space. The Antares team hails from SpaceX, the White House, the Pentagon, the Department of Energy, MIT, Rigetti Computing, General Atomics, Relativity Space, Ursa Major, and National Laboratories like Idaho, Oak Ridge, Los Alamos, and Savannah River. Antares has raised over $600M in venture capital from top-tier investors and has hundreds of million-dollars on contract with the military services, NASA, and the Department of Energy. About the Team As a Senior Space Thermal Engineer at Antares, you will own and drive the thermal design and analysis of a space nuclear vehicle, including the reactor, spacecraft, and heat rejection systems. You will develop, validate, and anchor thermal models to experimental and test data, using those models to guide early architecture decisions, system-level integration, and hardware design trades. This role will focus primarily on high-temperature thermal management for space nuclear systems, including reactor heat transport and radiator architectures, while also supporting traditional low-temperature spacecraft radiator design where required. You will work closely with reactor, fluids, mechanical, test, and systems engineers to define thermal management architectures, evaluate heat rejection system configurations, identify data gaps, and mature thermal hardware integration approaches from concept through test-informed design. Role and Responsibilities * Construct, own, and validate thermal models for the reactor core, spacecraft, radiator systems, and integrated vehicle thermal response. * Anchor thermal models to experimental, analytical, and test data wherever available; quantify uncertainty and improve model fidelity over time. * Identify gaps in thermal, materials, coolant-loop, radiator, and reactor heat-transfer data, and work with test engineers to define, execute, and interpret required tests. * Develop and analyze space nuclear thermal management architectures, including reactor heat transport, coolant loops, radiator systems, and integrated heat rejection systems. * Generate, compare, and downselect heat rejection system configurations across performance, mass, temperature, integration, reliability, manufacturability, and operational constraints. * Build system-level thermal models to assess vehicle-level performance, transient response, operating limits, and subsystem integration impacts. * Create tools, methods, and analysis processes for predicting radiator thermalization behavior, heat rejection system performance, operating characteristics, and integrated thermal response across the vehicle. * Investigate and develop thermal hardware integration approaches, including coolant loop architectures, radiator panel integration, heat pipe coupling, panel-to-structure interfaces, and heat-transfer paths. * Support early-stage concept development through modeling-driven design trades, first-principles analysis, and rapid evaluation of thermal system options. * Partner with reactor, mechanical, fluids, materials, test, and systems teams to ensure thermal design assumptions are reflected in hardware requirements, test plans, and design reviews. * Produce and review technical documentation, including thermal analyses, model validation reports, test plans, design trade studies, interface requirements, and design review materials. * Participate in formal and informal design reviews, ensuring thermal architecture, model assumptions, margins, risks, and verification approaches are clearly documented Basic Qualifications * Bachelor’s degree in Mechanical Engineering, Aerospace Engineering, Nuclear Engineering, Thermal Sciences, or a related technical discipline. * 5+ years of experience in thermal engineering, thermal analysis, heat transfer, spacecraft thermal systems, nuclear systems, high-temperature systems, or closely related hardware development. * Strong fundamentals in conduction, convection, radiation, transient heat transfer, thermal-fluid systems, and system-level thermal modeling. * Experience building and validating thermal models using test data, experimental data, or flight/hardware data. * Experience performing thermal design trades and communicating model assumptions, uncertainty, margins, and design implications to cross-functional engineering teams. Preferred Skills & Experience * Master’s degree or higher in Mechanical Engineering, Aerospace Engineering, Nuclear Engineering, Thermal Sciences, or a related field. * Experience with spacecraft thermal control systems, radiators, heat pipes, thermal straps, louvers, MLI, coatings, spacecraft environmental interfaces, or orbital thermal analysis. * Experience with high-temperature thermal systems, nuclear thermal systems, reactor heat transport, Brayton/Rankine/Stirling-adjacent thermal architectures, pumped loops, liquid metal coolants, gas coolants, or refractory materials. * Experience developing or analyzing heat rejection systems for space, nuclear, defense, aerospace, or high-reliability energy systems. * Strong familiarity with Python and Git-controlled code repositories. * Familiarity with thermal modeling and simulation tools such as Thermal Desktop, SINDA/FLUINT, OpenTD, ANSYS, COMSOL, STAR-CCM+, or Fluent. * Experience developing reduced-order models, sizing tools, parametric trade tools, or integrated system models for thermal architecture studies. * Experience designing, executing, or interpreting thermal vacuum, component-level, coolant-loop, heat pipe, radiator, or high-temperature heat-transfer tests. * Understanding of radiator performance drivers, including view factors, emissivity, absorptivity, fin efficiency, thermal spreading, panel thermalization, degradation, and environmental effects. * Experience with coolant loop architecture, pump/valve/heat exchanger integration, pressure drop, flow stability, startup/shutdown transients, or two-phase/single-phase thermal-fluid systems. * Experience integrating thermal hardware into aerospace or nuclear systems, including structural interfaces, thermal expansion, manufacturability, inspection, reliability, and operations constraints. * Strong technical judgment in ambiguous design spaces, with the ability to make progress using incomplete data while clearly identifying risks and validation needs. * Strong communication skills, including the ability to explain complex thermal architectures, model assumptions, trade results, and test implications to engineers, program stakeholders, and leadership. Salary Range * Senior Thermal Analyst - $145,000 - $185,000 Location * We are located in Torrance, CA in a 322,000 square foot, brand new facility featuring large open spaces for team collaboration, R&D, and production, as well as easy access to the 405, 105, and 110 freeways. Our facility is in the heart of Los Angeles' vibrant emerging tech ecosystem alongside many other high growth startups and enterprises. Culture At Antares, we like to specifically tie each role to our founding document’s set of values–here are the top five cultural values we think you should believe at your core to be successful: * Think in Systems - Energy and Defense are complex ecosystems with numerous stakeholders with competing priorities, conflicting policies, perverse incentives, and emergent and path-dependent properties. First principles thinking alone is insufficient. Think probabilistically and then take action. “If you want to be certain, then you are apt to be obsolete.” Over-optimizing the components often degrades the system * Obsess over the End User - The customer and end user are often not the same. We will never build globally competitive commercial products if we lose sight of our end users and their entire interaction with the product life cycle * Be Unconstrained by Convention - Our only limits are the laws of physics. Many, even experts, will say what we are working on is impossible. They said the same about SpaceX reusing rockets. Generationally impactful companies, by definition, must accomplish the seemingly impossible. If it were easy, it would have already been done. Never shy away from a solution because it has never been tried before, and never choose to do something because that's “how it's always been done” * Go Where the Work Is - Never miss a chance to meet a customer, user, or stakeholder face to face, even if that means hopping on a plane. If you can’t make it, find a teammate who can channel your intentions and go in your place. Deep work can be done from anywhere, but we believe teams are built in person, and aim to maximize our time together * Operate in the Grey - Embrace nuance in pursuit of truth. Question every fundamental assumption Equal Opportunity Antares is an Equal Opportunity Employer. Employment decisions are based solely on merit, competence, and qualifications, without regard to race, color, religion, gender, national origin/ethnicity, veteran status, disability status, age, sexual orientation, gender identity, marital status, mental or physical disability, or any other legally protected status. ITAR REQUIREMENTS To conform to U.S. Government export regulations, applicant must be a (i) U.S. citizen or national, (ii) U.S. lawful, permanent resident (aka green card holder), (iii) Refugee under 8 U.S.C. § 1157, or (iv) Asylee under 8 U.S.C. § 1158, or be eligible to obtain the required authorizations from the U.S. Department of State. Learn more about the ITAR here.

Senior Thermal Engineer - Space

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