The Underdogs Taking On SpaceX [Stoke Space 2025]

Key Concepts

• Full Reusability: Stoke Space is dedicated to developing fully reusable rockets, positioning themselves as a key competitor to SpaceX in this domain.
• Zenith Engine: Their core technology is the Zenith engine, a full-flow stage combustion cycle engine utilizing a single turbo pump for all 30 thrusters.
• Rapid Iteration & Additive Manufacturing: Stoke Space employs a “speedrun” approach to development, leveraging additive manufacturing and in-house testing infrastructure for quick design cycles.
• In-House Development: The company designs and builds a significant portion of its hardware and software in-house, including avionics, actuators, and a configuration management system (Bolt Line).
• Scalability: The engine and vehicle architecture are designed for significant scalability, potentially competing with larger launch vehicles.

Hopper Development & Initial Engine Testing

The initial Hopper vehicle (structure number two) underwent a limited test flight in Moses Lake, focusing on Thrust Vector Control (TVC) impulse measurement and Guidance, Navigation, and Control (GNC) algorithm validation. This flight utilized only 15 of the engine’s 30 chambers due to propellant restrictions. The engine itself has accumulated thousands of seconds of test time and remains in good condition. Early engine tests were conducted without a heat shield, progressing to fully instrumented tests with a more powerful and refined engine.

Zenith Engine Technology & Design

Stoke Space’s Zenith engine is a full-flow stage combustion cycle engine, a decision finalized recently. It utilizes a single turbo pump (one for oxygen, one for fuel) to power all 30 thrusters and employs an expander bleed cycle. The engine operates at approximately 5,000 PSI, with the main chamber exceeding 2,000 PSI, prioritizing low turbine temperatures for extended life and reusability. Current performance targets an ISP slightly north of 420 seconds at a chamber pressure of 2200 PSI. A key design element is a single valve controlling four flow rates within each thrust pod, reducing complexity. The nozzle design is optimized for efficiency at different altitudes, utilizing a dual-bell nozzle extension. The engine is currently capable of at least double its initial 100,000 lbs of thrust.

Materials & Manufacturing

Stoke Space strategically integrates additive manufacturing into its processes, particularly during iterative design phases. They are currently 3D printing nozzle panels, joining them together to form complete nozzles. The Zenith chamber itself was produced directly from a 3D print and refined using Electrical Discharge Machining (EDM). The engine utilizes pure copper for the chamber, deemed sufficient for current performance requirements. The heat shield is integral to the engine cycle, acting as a heat exchanger, and is tested with a water sprayer system to simulate both ground and space environments.

Avionics, Software & Infrastructure

Stoke Space maintains an in-house avionics lab, designing custom circuit boards, electromechanical actuators (EMAs), and communication systems. They utilize a “hardware-in-the-loop” simulation environment for flight simulations and operational procedure development. A unique in-house software platform, Bolt Line, manages configuration, procurement, build procedures, test procedures, and launch procedures, tracking the heritage of each part for predictive and AI-driven maintenance. Significant investment has been made in testing infrastructure at Moses Lake, including a Zenith test stand with six-degree-of-freedom thrust measurement, a structures test stand, and a COPV (Common Oxidizer Pressurization Vessel) test cell. An ejector system utilizes engine exhaust to create a vacuum for nozzle extension testing.

Vehicle Development & Flight One

The company is building a first-stage flight article using laser welding techniques. The upper stage features a modified heat shield design with a slant for cross-range control during re-entry, though this feature will not be utilized on the initial flight. Slush baffles are integrated into the oxygen tank to mitigate propellant sloshing. The first flight is focused on achieving a high-energy orbit, prioritizing orbital insertion over re-entry testing. Landing legs will not be included on either stage for this initial flight, with a re-entry test planned for a later stage. The upper stage will perform a hot separation and enter an escape trajectory. The Florida launchpad was structurally completed within 11 months of environmental assessment approval and is expected to be operational by year-end.

Company Culture & Future Outlook

Stoke Space operates under a pragmatic company culture, summarized by the rules: "Don't screw it up," "No licking," and "Do epic things." The team believes full and rapid reusability is the inevitable future of spaceflight and prioritizes answering fundamental engineering questions to enable scalability. They are considering scaling the architecture further, potentially to compete with larger rockets like Starship, driven by market demand.

Conclusion

Stoke Space is aggressively pursuing full and rapid reusability in spaceflight through the development of the Zenith engine and Nova vehicle. Their commitment to in-house development, rapid iteration, and strategic use of additive manufacturing, coupled with a robust testing infrastructure, positions them as a significant disruptor in the launch industry. The company’s focus on scalability and a belief in the inevitability of full reusability underscores their ambitious vision for the future of space access.