Archimedes: The Engine Forging Rocket Lab’s Next Generation

From Small Satellites to Mega-Constellations: The Strategic Leap

In the commercial space industry, Rocket Lab etched its identity as the undisputed leader of a market it helped create: dedicated small-satellite launch. The company’s Electron rocket, a sleek carbon-fiber vehicle, proved to be a resounding success. It has become the second most-frequently launched rocket in the United States, known for its reliability and a launch cadence that has, at times, outpaced nearly every other launch provider on Earth. Electron gave small satellite operators something they had never possessed before – control. No longer forced to “rideshare” on a giant rocket, waiting months or years for a slot, they could buy a dedicated launch, to a specific orbit, on their own schedule.

This success illuminated a stark business reality. The company’s trajectory, as its leadership has acknowledged, is no longer defined just by Electron flights. This isn’t an abandonment of a successful program but a candid recognition of its limits. The small-launch market, while a vital niche, represents just a “small slice” of the multi-billion-dollar space economy. When the fundamental economics of space launch are measured in “dollars per pound to orbit,” larger rockets are simply more efficient. The vast majority of the market, both in satellite mass and contract value, remained just out of Electron’s reach.

This realization sparked one of the most significant strategic pivots in the modern space race. Rocket Lab is aggressively moving up the value chain, transitioning from a small-launch provider to a vertically-integrated aerospace power. The physical lynchpin of this entire strategy is a new, massive rocket named Neutron, and its powerhouse is an engine called Archimedes.

Neutron is designed to hit the “sweet spot” of the modern launch industry. It’s a medium-lift rocket designed to carry a 13,000-kilogram payload (approximately 28,700 pounds) to low Earth orbit. This single capability is a ‘game-changer’ for the company. It’s a leap in capacity that expands Rocket Lab’s addressable market from just a few percent of all satellites to an estimated 98% of all payloads projected to launch in the coming decade.

The primary target for this new capability is the “mega-constellation” market. These are networks of hundreds or even thousands of satellites designed for global internet, Earth observation, or communications. Deploying these massive constellations is a task for which Electron is entirely unsuited, but for which Neutron is “ideally sized.” It can launch large batches of satellites at a time, making constellation deployment far faster and more economical.

This move isn’t just about launching satellites for other companies. It’s a powerful enabler for Rocket Lab’s own ambitions. The company has been clear about its intention to “move up the value chain,” beyond manufacturing and launch, into the lucrative world of “space applications.” Neutron is the key that unlocks this future, giving Rocket Lab the in-house capability to deploy its own constellations. The company is already developing the hardware, such as its “Flatellite” satellite bus, to compete in the “Direct-to-Consumer” market. The Archimedes engine isn’t just powering a rocket; it’s powering Rocket Lab’s transformation into an end-to-end space company, from satellite design and manufacturing to launch and, ultimately, data services.

This pivot also unlocks another set of high-value customers: government and national security. The U.S. Space Force’s National Security Space Launch (NSSL) program, which procures launches for the nation’s most sensitive intelligence and military satellites, is dominated by heavy-lift, high-cost rockets. Neutron is being positioned as a more flexible, cost-effective, and responsive American-made option to compete for these critical contracts. It’s also been selected for evaluation by the U.S. Air Force for its futuristic “point-to-point” cargo program, which imagines using rockets to deliver cargo anywhere on Earth in under an hour.

The Archimedes engine is the heart of this entire corporate bet. It’s the machine that enables the rocket that enables the business model. It represents a “bet-the-company” investment, a massive leap in technical capability designed to carry Rocket Lab from its startup roots into direct competition with the industry’s established giants.

A Primer on Rocket Propulsion for the Modern Era

To understand what makes the Archimedes engine special, it’s helpful to first understand what a modern rocket engine is and how it works. At its most basic, a liquid-propellant rocket engine is a device for creating and sustaining a continuous, controlled explosion, all directed in one direction.

Like a car’s engine, it burns a fuel to create hot gas. But unlike a car engine, it can’t “breathe” air from the atmosphere. In the vacuum of space, there is no air. This means a rocket must carry its own oxygen in a liquid form, called an “oxidizer.” An engine that uses both a separate fuel and a separate oxidizer, like Archimedes, is known as a “bipropellant” engine.

While engines are incredibly complex, they can be broken down into three key parts for a non-technical audience.

First is the Combustion Chamber, which can be thought of as the engine’s “furnace.” This is the high-pressure, superheated vessel where the fuel and oxidizer are injected, mixed, and ignited to create a violent, expanding cloud of extremely hot gas.

Second is the Nozzle, the iconic, bell-shaped “funnel” that everyone associates with a rocket. The nozzle’s job is deceptively simple but vital: it takes the chaotic, high-pressure gas from the furnace and accelerates it to incredible speeds, often several miles per second. This escaping gas produces the “push,” or “thrust,” that moves the rocket.

Third, and most complex, are the Turbopumps, which are the “heart” of the engine. A large rocket engine, like Archimedes, must burn tons of propellant every single second. The propellants can’t just be pushed out of their tanks by gas pressure; this “pressure-fed” system would require the tanks to be so thick and heavy to contain the pressure that the rocket would never get off the ground. The solution is a “pump-fed” engine. A turbopump is an incredibly sophisticated turbine, like a miniature jet engine, that spins at tens of thousands of RPM to pump propellants from the low-pressure fuel tanks into the high-pressure combustion chamber. The single most important design choice in a modern rocket engine is how this turbopump system is powered.

When engineers talk about engines, they use two key metrics to measure performance.

The first metric is Thrust. This is the easy one. It’s the engine’s raw power. How hard does it push? This is typically measured in pounds-force (lbf) or Newtons (kN).

The second metric is Specific Impulse (Isp). This is the engine’s efficiency – its “gas mileage.” It’s a measure of how much push the engine gets from a given amount of propellant. It’s measured in “seconds,” but the concept is simple: a higher number is better. An engine with a high specific impulse is more efficient, allowing a rocket to achieve more “delta-v” (change in velocity) for the same amount of fuel, or to carry more payload to the same destination.

Finally, there is a fundamental problem that splits engine design in two: the atmosphere. The “funnel” or nozzle of an engine has to be shaped differently depending on where it’s being used.

At sea-level, the rocket is surrounded by thick air pressure. This pressure “squeezes” the exhaust plume as it exits the nozzle. To be efficient, a sea-level engine must have a relatively “tight” or “short” nozzle. This nozzle is designed to push the exhaust out at a pressure that is close to the air pressure outside, ensuring all the energy is directed straight down.

In the vacuum of space, there is zero air pressure. The exhaust gas from the furnace wants to expand outward in every direction, forever. A “vacuum-optimized” engine is designed to capture this expansion. It has a much, much larger and wider nozzle bell. This massive bell “catches” the expanding gas and directs it, capturing every last bit of energy that would otherwise be wasted. This is why a vacuum engine is always more efficient (has a higher specific impulse) and often more powerful than its sea-level counterpart. This is also why the first stage of a rocket (the booster) and the second stage (the part that goes to orbit) have very different-looking engines.

The Reusability Problem: Why Methane is the New Fuel of Choice

The first and most fundamental design choice for Archimedes was its “food” – the propellants it burns. This decision, made years before any metal was cut, dictates almost everything else about the engine’s performance, its complexity, and, most importantly, its ability to be reused. The Archimedes engine burns liquid oxygen (LOX) as its oxidizer and liquid methane (CH4) as its fuel. This combination is known as “methalox,” and it has become the “fuel of choice” for the new generation of reusable rockets.

To understand why, it’s best to look at the two traditional alternatives: kerosene and hydrogen.

The “old guard” of rocket fuels is kerosene, specifically a highly-refined, rocket-grade version called RP-1. This is the fuel that powered the Saturn V missions to the Moon, the reliable Russian Soyuz rocket, and, most notably, the SpaceX Falcon 9 and its Merlin engines. Kerosene has a lot of advantages. It’s “dense,” meaning it packs a lot of energy into a relatively small tank. It’s also a liquid at room temperature, which makes it far easier, safer, and cheaper to handle than the super-cold (cryogenic) liquids that must be stored at hundreds of degrees below zero.

But for reusable rockets, kerosene has one devastating, “show-stopper” flaw: it burns dirty. Kerosene is a mix of complex, long-chain hydrocarbon molecules. When it burns, it doesn’t combust perfectly. It leaves behind a residue, a black, sticky “soot” known as “coking.” This is the same kind of gunk that builds up in a car’s engine over many years, but in a rocket engine, it happens in minutes.

For an expendable rocket that is used once and thrown away, this doesn’t matter. But for a reusable one, it’s a disaster. This soot builds up inside the engine’s most delicate and high-performance components – the turbopump turbines, the injector plates, and the tiny, life-saving cooling channels. This means that after every single flight, a kerosene-based engine must be extensively inspected, cleaned, and refurbished. This process is time-consuming, labor-intensive, and expensive. It fundamentally breaks the dream of “rapid reusability.” You can’t just “land and relaunch” if you have to spend weeks scrubbing soot out of your engines.

The other main option is liquid hydrogen (hydrolox). This is the fuel that powered the Space Shuttle’s main engines. Hydrogen is the “clean” fuel. It’s the most efficient chemical propellant known, giving the highest possible “gas mileage” (Isp). When it burns with oxygen, its only exhaust product is pure water.

But hydrogen, for all its performance, is a “nightmare” to work with. It’s the least dense fuel in the universe, meaning you need absolutely enormous, bulky, and heavy fuel tanks to hold it, which adds weight and drag to the rocket. It must also be stored at temperatures near absolute zero, making it extremely dangerous and difficult to handle. It has a nasty habit of “embrittling” metal, making it brittle and weak, and its tiny molecules can leak through the smallest, microscopic imperfections.

This is where methane, the “Goldilocks” fuel, comes in. In the last decade, nearly every new, large rocket engine – Archimedes, SpaceX’s Raptor, and Blue Origin’s BE-4 – has been designed to burn methane.

Methane (CH4) is a simple, single-carbon molecule. Its greatest advantage is that it burns incredibly clean. It leaves behind no soot, no “coking.” This is the entire foundation for a “rapidly reusable” rocket. It means an engine like Archimedes can, in theory, fly, land, refuel, and fly again with “minimal refurbishment.” The engines don’t need to be disassembled and scrubbed between flights. This single factor is an economic one, not just an engineering one. It’s what makes a high-flight-rate, low-cost business model possible.

Methane also represents a “good-enough” performance compromise. Its “gas mileage” (Isp) is significantly better than kerosene’s. And while it’s not as dense as kerosene, it’s far, far denser than liquid hydrogen. This means it doesn’t need the enormous, heavy tanks that hydrogen requires.

As a final operational bonus, liquid methane and liquid oxygen are both cryogenic liquids with very similar boiling points. This simplifies the rocket’s internal plumbing and the design of the tanks, particularly the “common bulkhead,” or the single wall that separates the two propellants inside the rocket. This choice of fuel signals that Rocket Lab is designing Archimedes not just for raw performance, but for operational efficiency, reliability, and, above all, a low-cost, reusable future.

A Tale of Two Engine Cycles: The Great Design Change

With the fuel selected, the Rocket Lab team faced its next, and most difficult, decision: the “engine cycle.” As the primer explained, a large engine needs a turbopump, and that pump needs a power source. The “engine cycle” is the engineering name for this internal power system. This is the most complex part of rocket science, and it’s where the Archimedes story takes its most important and counter-intuitive turn.

There are two main ways to power a turbopump: the simple way, and the complicated way.

The simple and long-proven choice is called the “gas-generator” (GG) cycle, also known as an “open cycle.” This is the rugged, reliable design used on the Falcon 9’s Merlin engine and the Saturn V’s F-1.

A “gas-generator” cycle works by having what is essentially a second, tiny rocket engine (the “gas generator” or “pre-burner”) bolted to the side of the main one. A small amount of propellant is “tapped” from the main lines and burned in this pre-burner. The hot, high-pressure exhaust from this isn’t used for thrust. Instead, it’s blasted at a turbine, like a windmill, causing it to spin at incredible speed. This spinning turbine is connected to the main pumps, driving them. After spinning the turbine, the spent, smoky exhaust gas is simply “dumped overboard.” It’s “lost.” This is the “open” part of the cycle. On a Falcon 9 launch, this is visible as a separate, sooty exhaust plume coming from the side of the engine bell. The pros of this system are that it’s “low risk,” relatively simple, and easier to build. The pressures are lower, which puts less stress on the components. The con is that it’s “wasteful.” The propellant used to drive the pumps – which can be 2% to 3% of the total propellant flow – is thrown away and doesn’t help push the rocket.

The complex, high-performance choice is called the “staged combustion” (SC) cycle, or “closed cycle.” This is the “holy grail” of rocket engine design, used on the Space Shuttle’s main engines and SpaceX’s Raptor. The philosophy of a closed-cycle engine is simple: “nothing is wasted.”

In this design, instead of tapping off a small amount of propellant, the engine sends the entire flow of one propellant (plus a little bit of the other) through the pre-burner to spin the turbine. This creates a massive amount of hot, high-pressure gas, which spins the turbine with incredible force. But – and this is the key – instead of being “dumped overboard,” this hot gas is then “piped back into” the main combustion chamber to be fully burned. Every single drop of propellant is ultimately used to create thrust.

The “pro” is that this is the most efficient system possible. It allows for extremely high pressures in the main chamber and gives the best “gas mileage” (Isp) of any chemical rocket. The “con” is that it is mind-bogglinglycomplex and dangerous to build. To work, the pre-burner must run at a higher pressure than the main combustion chamber, which is already at an insane pressure. The plumbing and turbines must survive being blasted by hot, high-pressure, chemically-reactive gases.

The specific version Archimedes uses is called “Oxidizer-Rich Staged Combustion” (ORSC). This is a notoriously difficult cycle because it means the pre-burner is “oxidizer-rich.” It’s pumping hot, gaseous oxygen. Hot, gaseous oxygen is one of the most terrifying substances in engineering; it wants to violently burn everything it touches, including the metal of the engine itself. Mastering it requires exotic, almost-magical metal alloys that can survive in this corrosive, high-temperature environment.

This brings us to the great Archimedes “pivot.”

When Rocket Lab first announced Archimedes in December 2021, it was, logically, a “gas-generator” (GG) engine. This made perfect sense. It was the “low risk” choice for a company that had “zero experience with turbines” at this scale (its smaller Rutherford engine uses electric pumps, a technology that gets too heavy for large engines).

Then, in September 2022, Rocket Lab announced a complete reversal. They were scrapping the simple GG design and switching to the “Oxidizer-Rich Staged Combustion” (ORSC) cycle – one of the most difficult engine cycles to build.

The reason for this pivot is the entire key to the Archimedes philosophy. The official rationale was that as they designed the GG engine, they found they “could not get the performance they needed… without pushing the turbine temperature and other factors beyond their preset limits.”

This is a critical piece of engineering-speak. In simple terms, to get the power Neutron needed from the “simple” GG engine, they had to “redline” it. The engine had to run too hot, too stressed, and too close to its breaking point. A “redlined” engine is the exact opposite of what you want for a “rapidly reusable” rocket. It’s an engine that will wear out fast and require constant, expensive maintenance.

So, Rocket Lab made a brilliant and counter-intuitive choice. They adopted the more advanced and more efficient ORSC cycle specifically so they could run it at a lower-stress level.

Because the ORSC cycle is so much more efficient, it doesn’t need to be pushed hard to get the same amount of power. Rocket Lab could “de-rate” it, designing it to run at much lower pressures and temperatures than its theoretical limits. They are using a high-performance type of engine but running it “gently.” This is the genius of the design: it achieves both high efficiency (because it’s a closed-cycle) and low stress (because it’s de-rated), which is the perfect combination for longevity and rapid reuse.

This pivot came at a cost. The original 2024 launch target for Neutron was almost certainly based on the simpler GG engine. Switching to the monstrously complex ORSC cycle – which requires mastering new physics, new manufacturing techniques, and exotic metallurgy – is a massive engineering reset. The subsequent slip of Neutron’s first launch to “mid-2025” is the direct and unavoidable price of making this difficult, long-term-focused decision. Rocket Lab chose a harder development problem today to have an easier, more profitable operations problem for decades to come.

Designing for Decades: The Archimedes Philosophy

The “low-stress” solution to the engine cycle problem isn’t just a technical fix; it’s the core of the entire Archimedes design philosophy. This philosophy can be summed up in three words: “Reliability Over Performance.”

From its inception, the primary purpose for the Archimedes engine was “not for power nor precision, but to be reused.” While competitors in the launch industry often engage in a “space race” to build engines with the highest possible thrust and chamber pressure – pushing their hardware to the absolute limits of material science – Rocket Lab has intentionally taken the opposite approach.

Archimedes is “intentionally designed to operate within medium-range capability.” By adopting the high-efficiency ORSC cycle and then “de-rating” it, Rocket Lab is running the engine far below its potential redline. This “low-stress” approach “lowers thermal and operational strains” across the entire engine. The turbopumps don’t have to spin as fast. The combustion chamber doesn’t have to contain as much pressure. The cooling channels don’t have to manage as much heat.

The economic advantage of this is significant. An engine that runs “gently” is an engine that lasts. Lower temperatures and lower pressures mean far less wear and tear on pumps, seals, injector plates, and the chamber lining. This is what allows Rocket Lab to confidently set a “minimum reuse target of up to 20 launches per engine.” This isn’t just an engineering goal; it’s the central business metric that makes the Neutron rocket economically viable.

This entire “low-stress” engine philosophy is only possible because of a brilliant, systems-level trade-off with the rest of the Neutron rocket. Neutron is “the world’s first carbon composite large launch vehicle.” Rocket Lab is a world-leader in carbon composite manufacturing, having perfected the process with its Electron rocket. By building the Neutron’s entire airframe and tanks out of this advanced, lightweight material, they are making the rocket itself significantly lighter than a traditional rocket built from aluminum.

Because the rocket’s structure is so “lightweight,” its engines “do not need the immense performance and complexity typically associated with larger rockets.” Rocket Lab is, in effect, “spending” its expertise in carbon composites to “save” itself from needing a hyper-performance, high-stress engine. They made the airframe light so the engine could be reliable. This is a holistic trade-off that competitors, who are building heavier metal rockets, cannot make. They are forced to chase higher and higher performance from their engines, running them “hotter” and closer to their limits, which in turn makes rapid reusability a much harder problem to solve.

Rocket Lab is making a bet that the total cost of ownership – which includes development, manufacturing, and, most importantly, refurbishment – is more important than raw, on-paper performance. They are deliberately sacrificing some “gas mileage” and thrust, because they’ve made the vehicle itself so light. They believe the money saved from an engine that requires “minimal refurbishment” will, in the long run, far outweigh the small performance penalty on any single flight.

The “Big-Book” Comparison: Archimedes vs. Its Rivals

The Archimedes engine is not being developed in a vacuum. It is entering a “medium-lift” market that is currently dominated by one rocket and is about to be challenged by another. The success of Archimedes and Neutron will be defined by how it stacks up against its two primary competitors: SpaceX’s veteran Merlin engine (on the Falcon 9) and Blue Origin’s new BE-4 engine (on the ULA Vulcan).

Archimedes (Neutron) vs. Merlin (Falcon 9)

This is the established champion versus the new challenger. The Falcon 9, powered by nine Merlin engines, is the most-flown and most-reused rocket in history.

• Propellant: This is the biggest difference. Archimedes runs on clean-burning methane. Merlin runs on “sooty” kerosene (RP-1). This gives Archimedes a massive theoretical advantage in rapid reusability and reduced refurbishment time. The Falcon 9’s engines require significant cleaning to deal with kerosene’s “coking” problem.
• Engine Cycle: Archimedes uses the highly efficient, “closed-loop” ORSC cycle. Merlin uses the simpler, but more “wasteful,” “open-loop” Gas-Generator (GG) cycle. This means that for every pound of propellant, Archimedes is a more efficient engine.
• Performance: This is where it gets interesting. A single Merlin 1D engine is actually more powerful at sea level (producing ~845 kN of thrust) than a single Archimedes (~730 kN). This again highlights Rocket Lab’s “low-stress” philosophy. They aren’t trying to beat Merlin on raw power; they’re trying to beat it on longevity and operational cost.
• Market Niche: The Neutron rocket is not a direct “Falcon 9 killer.” It’s an “interceptor” that attacks a specific price and performance gap. The Falcon 9 can lift much more (17,400 to 22,800 kg) but also has a public price tag of over $70 million. Neutron, lifting 13,000 kg for a target price of $50-55 million, is the perfect, “right-sized” option for a satellite customer who doesn’t need the Falcon 9’s full power and doesn’t want to pay for capacity they aren’t using.

Archimedes (Neutron) vs. BE-4 (Vulcan)

This is the real “apples-to-apples” fight between the two next-generation, American-made, methalox engines.

• The “David vs. Goliath” Reality: While they share the same fuel (methane) and the same advanced engine cycle (ORSC), they are in completely different classes. The Blue Origin BE-4 is an absolute monster. A single BE-4 engine produces 2,400 kN (550,000 lbf) of thrust – over three times the power of a single Archimedes.
• Divergent Philosophies: This size difference reveals the two companies’ opposing design strategies. The BE-4 is a “brute-force” engine, designed in a pair to lift the massive, heavy, traditional-metal-tank Vulcan rocket. Archimedes is a “finesse” engine, designed to work in a cluster of nine to lift a lightweight, carbon-composite rocket.
• Reusability Difference: This is the most critical distinction. The nine Archimedes engines on Neutron are designed for the propulsive “return-to-launch-site” landing and reuse of the entire first stage, just like a Falcon 9. The two BE-4 engines on the Vulcan rocket are designed for a much different, more complex “engine-only” recovery. This plan involves the engines detaching from the rocket, deploying a parachute, and being caught in mid-air by a helicopter – a concept that has yet to be proven at this scale.

The Archimedes engine is not just a new design; it’s a new way of manufacturing. It’s a “clean-sheet” engine, conceived from the ground up to be built using additive manufacturing, the industrial term for 3D printing.

This isn’t a case of using 3D printing for a few small, non-critical brackets. Approximately 90% of the Archimedes engine’s total mass is 3D-printed material. This includes the most “critical components” of the engine, the parts that must withstand the most extreme temperatures and pressures. Rocket Lab is 3D printing its massive turbopump housings, the complex pre-burner (where the first-stage combustion happens), the main combustion chamber components, and all the various valve housings.

This “3D-printing-first” approach provides three massive advantages: speed, complexity, and cost.

First, Speed. Additive manufacturing allows for “quick iterations.” In a traditional engine program, if engineers want to test a new turbopump design, they must wait months, or even a year, to create new molds, cast the part, and machine it. With 3D printing, an engineer can tweak a design in a computer, send the file to the printer, and have the new, full-scale metal part in their hands in a matter of days. This “fast, scalable workflow” is what makes Rocket Lab’s aggressive development timeline possible. It allows the team to design, print, test, break, and iterate at a pace that is impossible with old-school manufacturing.

Second, Complexity. 3D printing allows engineers to design parts that were “impossible” to build before. The most critical part of an engine is its cooling. The combustion chamber is hot enough to melt any known metal, so it must be “cooled” by a network of tiny, internal channels that flow propellant through the chamber walls. With 3D printing, these impossibly complex, intricate channels can be printed directly into the structure of the engine, creating a single, solid piece that is both stronger and more efficient than a part made of many-welded-pieces.

Third, Cost. This is all part of a “factory-driven model” to reduce production costs and time. By building its production line around automation and 3D printing, Rocket Lab is streamlining the entire process from raw material to a finished, tested engine.

To support this new engine, Rocket Lab has built a continental-scale production line, a massive leap in industrial maturity from its all-in-one factory in New Zealand. The journey of a single Archimedes engine now spans the entire United States.

Stop 1: Long Beach, California. This is the “brain” and “birthplace” of the engine. Rocket Lab’s 144,000+ square-foot Engine Development Complex is located here. This is where the engines are designed, where the massive 3D printers turn metal powder into parts, and where those parts are assembled into a complete Archimedes engine.

Stop 2: Stennis Space Center, Mississippi. This is the “proving ground.” The completed engines are carefully shipped from California to the Archimedes Test Complex at this historic NASA facility. This is where they are installed on a massive test stand and “qualified” for flight.

Stop 3: Wallops, Virginia. This is the “launch pad.” Rocket Lab is building a new, 250,000-square-foot Neutron Assembly & Integration Complex adjacent to its launch pad. The “flight-qualified” engines from Stennis are shipped here to be integrated into the carbon-composite Neutron rocket stages. This facility will also serve as the refurbishment center, where returned boosters are inspected, prepared, and stacked for their next flight.

This de-centralized, specialized production line – (1) R&D and Manufacturing in California, (2) Testing and Qualification in Mississippi, and (3) Final Assembly, Integration, and Launch in Virginia – is a classic industrial optimization strategy. It’s a “big company” move, proving that Rocket Lab is building a robust industrial process, not just a single rocket.

This manufacturing strategy is the key to Rocket Lab’s “production-first” development. They are betting that their 3D-printing-based design-build-test loop is so fast that the engine on the test stand is already 99% identical to the “production” engine. They are effectively merging the late-stage R&D and mass-production phases into one, gambling that they can go from “first test” to “flight-ready” faster than any company before them.

Breathing Fire: The Archimedes Test Campaign

The story of Archimedes’ development from a computer screen to a fire-breathing machine reached its climax in the hot, humid air of Mississippi. The entire test campaign is centered at the “Archimedes Test Complex” at NASA’s Stennis Space Center, America’s largest rocket propulsion test site.

Rocket Lab isn’t just building a small test pad; it’s leasing and upgrading the historic A-3 Test Stand. This is a massive, high-altitude test stand, a piece of national infrastructure originally built to test the J-2X engine for NASA’s canceled Constellation program. This stand is an engineering marvel, capable of testing engines with up to 1 million pounds of thrust and simulating the vacuum of space at altitudes of 100,000 feet. By leasing this existing stand, Rocket Lab saved itself years of construction time and hundreds of millions of dollars, allowing it to move straight to testing its large-scale engine.

The first full-scale hot fire wasn’t the beginning of the test campaign. It was the culmination of hundreds of “component, subsystem, and all-up system tests” throughout 2023 and 2024. This included “spin primes” (testing the turbopumps by flowing propellant through them without igniting) and “ignition tests” (testing the ‘spark-plug’ system that lights the engine).

The path to hot fire had two major milestones in 2024. On May 6, 2024, Rocket Lab announced it had completed the build of its first full Archimedes “development engine.” This was the first time all the 3D-printed parts, turbopumps, pre-burners, chambers, and intricate plumbing had been assembled into a single, complete unit. This engine was shipped from Long Beach and installed on the A-3 stand at Stennis.

Then, on August 8, 2024, the company announced its “Successful First Hot Fire.” This is the “moment of truth” for any new engine program. It’s the first time the engine is ignited to produce sustained, controlled thrust. It’s the most dangerous and most important test, the one that validates that the “clean-sheet design” actually works in the real world, and that the engine won’t tear itself apart.

The test was a complete success. Rocket Lab stated the engine “performed well” and “ticked off several key test objectives.” Most significantly, the company reported the engine test included “reaching 102% power.”

This “102%” figure is the first tangible, public proof that Rocket Lab’s entire “low-stress” design philosophy is not just a marketing claim. It proves that the engine’s 100% “operational” power level is not its “redline.” It has performance margin “in the tank.” It can be run comfortably at its 100% rating without being stressed. This single data point from the very first test was a massive validation of their counter-intuitive engineering bet.

With this successful hot fire, the Archimedes design is now “anchored.” This means no more major changes are needed; the design is locked for flight.

This milestone immediately triggered the next, most aggressive phase of Rocket Lab’s plan. The company announced it was moving “into full production of flight engines” in parallel with the ongoing “full qualification campaign.” This is the “production-first” gamble. While one engine is being “hot-fired flat out” on the test stand again and again to prove its reliability, the factory in California is already building the engines for the first set of flights.

This is a high-risk, high-reward strategy. The risk is that the qualification testing could reveal a fundamental flaw (like a resonance or a turbine-blade crack) that grounds the entire production line of engines they’ve already built. But the reward is that if they are right – if their 3D-printing-based design is as solid as the first test suggests – they will have shaved 12 to 24 months off a traditional development schedule. They will have a stockpile of flight-ready engines the moment qualification is complete, enabling Neutron to be, as they claim, the “fastest a commercially developed medium-class launch vehicle has been brought to market.”

Powering the Neutron: Engine Integration and Flight Profile

The Archimedes engine is a family of one. It’s a single engine design that powers both stages of the Neutron rocket, a critical manufacturing and logistics simplification. This “one engine, two forms” approach is a cornerstone of the rocket’s low-cost design.

The reusable First Stage, the booster, is powered by a cluster of nine Archimedes engines. This is the “sea-level” variant, with nozzles shaped to be efficient in the thick air of the atmosphere. When first announced, Neutron was slated to have seven engines. The number was increased to nine as a direct consequence of a major change in the rocket’s mission. The original plan called for an “ocean platform” landing, but this was scrapped in favor of a much more demanding “Return to Launch Site” (RTLS) propulsive landing. An RTLS landing requires the booster to completely reverse course in mid-air, fly all the way back to its launch pad, and land vertically – a maneuver that requires significantly more thrust and fuel. The two extra engines provide that thrust, as well as important “engine-out” reliability, meaning the rocket can still land safely even if one of its engines fails during the landing burn. Together, these nine sea-level engines produce just under 1.5 million pounds-force of thrust at liftoff.

The expendable Second Stage, the part that flies into orbit, is powered by a single Archimedes engine. This is the “vacuum-optimized” variant. As explained in the primer, this engine looks visibly different; it has a much larger, wider nozzle bell to make it highly efficient in the vacuum of space. This single engine produces approximately 200,000 pounds-force of thrust.

From a pure performance perspective, some have noted that this vacuum engine is “way too big” and “overpowered” for an expendable second stage. And if performance were the only goal, that would be true. But Rocket Lab is optimizing for cost.

By using the same core engine for both stages – sharing all “major components” like turbopumps, pre-burners, and injectors – Rocket Lab has to design, test, and build only one engine. They only need one R&D program, one set of test-stand tooling, and one manufacturing line. The small, theoretical performance penalty of having a “too-big” upper stage engine is a tiny price to pay for the enormous economic savings of a simplified and streamlined production system.

These engines are integrated into one of the most unique rocket designs ever conceived. The second stage is “hung” inside the first stage’s structure. The rocket’s payload fairing – the “nose-cone” that protects the satellite – is not a separate piece that gets thrown away. It’s integrated into the first stage, with two giant, “Hungry Hippo” jaws.

The flight profile is revolutionary. The nine Archimedes engines will fire to lift the rocket. After the first stage is spent, the “Hungry Hippo” fairing will open, and the second stage (with its single vacuum-Archimedes) will deploy and light its engine to continue to orbit. The jaws then close, and the entire first-stage booster – with its integrated fairing – uses its nine Archimedes engines to perform a propulsive landing back at the launch site. This means the Archimedes engines are responsible for safely landing both the booster and the payload fairings, a massive innovation that saves the cost of two of the most expensive parts of the rocket.

This entire system – the nine reusable methane engines, the single expendable vacuum engine, and the reusable carbon-composite airframe – is designed to hit that $50-55 million target launch price. This price point is specifically calibrated to “break… the launch monopoly” and create a new, disruptive, and competitive option for satellite operators who find the current market too big, too expensive, or too slow.

Summary

The Archimedes engine is far more than a new piece of rocket hardware. It is the physical embodiment of Rocket Lab’s corporate transformation. It’s the lynchpin in a grand strategy to leap from a successful, niche provider of small launches to a vertically-integrated, major player in the global space economy. It is, in short, the machine that will either make or break the company’s multi-billion-dollar ambitions.

Its design is a masterclass in deliberate, intelligent trade-offs. It burns clean-burning methane, not for raw performance, but to eliminate the “soot” that plagues the reusability of its kerosene-fueled competitors, a design choice aimed at operational economics, not just engineering.

It employs one of the most complex and efficient engine cycles ever developed, Oxidizer-Rich Staged Combustion, not to “redline” its power, but for the counter-intuitive purpose of running “gently.” This “low-stress” philosophy, enabled by the rocket’s lightweight carbon-composite body, is the key to a long, reliable life of 20 flights or more per engine, with minimal refurbishment between flights.

This philosophy is the foundation of Neutron’s entire business plan. It’s what will enable the rocket to be rapidly reusable, hitting its $50-55 million target price. This price point is a direct challenge to the current market, offering a “break in the launch monopoly” for the mega-constellation and national security customers that dominate 98% of all future payloads.

With the successful first hot fire in August 2024, the engine’s design is now “anchored” and “flight engines” are in full production. Archimedes is no longer a blueprint, a computer model, or a set of 3D-printed parts. It is a working, fire-breathing machine, and it is the engine that will carry Rocket Lab’s ambitions into the next era of the commercial space race.