The Spanish and French company Pangea is positioning itself as a go-to propulsion company within the aerospace industry. It first drew attention in 2021 with a successful demonstration of an aerospike engine in Germany. Four years on, testing is already underway for its larger, reusable Arcos engine, which is on course to become the first flight-ready aerospike engine in the world.
NSF spoke with Pangea’s founder and CEO, Adrià Argemí, to learn more about the technical journey and how the company is overcoming many historic hurdles to turn this long theorized engine concept into reality.
Aerospikes are considered by many to be the “holy grail” of propulsion. While the aerospike concept promises to deliver greater performance than conventional bell nozzles, designing one is not without its challenges, from cooling the engine to reducing the cost of manufacturing to make it viable. Whereas conventional engine nozzles are optimized for either sea-level or vacuum, aerospikes adapt naturally to changing atmospheric pressure and maintain efficiency at all altitudes.
Theoretically offering efficiency benefits of up to 15% over traditional rocket engines, aerospikes have been studied since the mid-20th century, when they were seen as the future of highly efficient propulsion. Early designs, however, were complex, costly, and didn’t integrate well with the cylindrical shape of most rockets.
Lockheed Martin’s VentureStar program and X-33 prototype made notable progress in the 1990s using a linear aerospike, but were cancelled amidst technical issues and escalating costs. The wedge shape of the X-33’s XRS-2200 engine is an example of how aerospike designs don’t all follow the classic toroidal design with a central spike. More recent advances in materials, additive manufacturing, and a growing demand for reusable, high-performance engines have since revived interest and look set to give aerospikes a second wind.
Reusability is key to the design of Pangea’s flagship Arcos aerospike engine. It’s even reflected in the company’s original logo, which used the stylised “A” from the Pangea name to suggest both an aerospike and the path to orbit and back. Formed in 2018, the company takes its name from the ancient Greek word for the single landmass supercontinent of the late Paleozoic Era and roughly translates to “all lands.” This interpretation also acknowledges the fact that the six co-founders hail from different countries, and reflects the multi-cultural nature of the company. Within its team of 70 people and counting, Pangea currently employs talent from around 16 countries.
Pangea’s Demonstrator Propulsion 1 aerospike engine, known as Demo P1. (Credit: Pangea Aerospace)
Argemí draws his expertise from a wealth of experience, working previously at Airbus and then Avio — the makers of the Vega rocket family. It was there that he met some of Pangea’s other co-founders, and a plan was forged to build a reusable micro-launcher with a better propulsion system. Over time, the plan was refined to specialise as a propulsion company, making highly efficient products which could then be supplied to rocket manufacturers.
Arcos will be the company’s first commercial product and is designed for upper-stage applications. It is significantly larger and more powerful than the company’s first Demonstrator Propulsion 1 engine — more commonly referred to as Demo P1.
Many lessons were learnt with this first aerospike demonstrator, and, with no playbook to refer to, new tools, software, and models had to be created. With a toroidal design, the Demo P1 was the world’s first aerospike engine to use liquid methane and liquid oxygen as propellants.
“We do believe it’s the propellant of the future,” Argemí notes, “and we’re seeing a lot of companies now switching to it. For us, it was a no-brainer.”
Pangea test fires the worlds first methalox aerospike engine, the Demo P1, in November 2021. (Credit: Pangea Aerospace)
The Demo P1 engine is capable of generating 20 kilonewtons of thrust and successfully ignited on its first attempt in November 2021 at the German Space Agency’s (DLR) Lampoldshausen test facility. The engine measured less than 25 cm in diameter, or roughly the size of an outstretched hand. By contrast, Arcos represents a massive scale-up from the Demo P1. Measuring around 3.5 m in diameter — a little under the diameter of a Falcon 9 — it is a 750 kilonewton engine with a mass of 75 tonnes.
Pangea has built reusability into the design of the Arcos from day one. “Being reusable is hard,” Argemí notes, “there are so many things that you have to take into account. In our case, we already introduced some variables to make sure, for example, that the chambers could withstand several cycles, as the Merlin on Falcon 9 is doing. There’s a lot of innovation in these engines. There were a lot of challenges and a lot of firsts.”
Initially, Pangea will target 10 missions for its reusable Arcos engine, which will introduce a number of complexities. “You have to do a lot of material characterization, a lot of analysis on low-cycle fatigue and how it would behave,” Argemí says.
Demo P1 has a single-chamber design, whereas Arcos has multiple chambers around its perimeter. The current design layout has 20 “thrusters” in a circle, which compromises a little efficiency but delivers a performance that’s close to the ideal aerospike concept. “Of course, you want to augment the number of chambers you have,” Argemí points out. “The more uniform the flow would be, the more like the theoretical perfect one [chamber design] you would actually get to.”
Render of the Arcos engine design (Credit: Pangea Aerospace)
The Arcos engine uses differential throttling across the ring for thrust vectoring, which could allow the engine to throttle down to around 50%. Differential throttling also avoids heavy gimballing hardware or moving parts in the design. “It’s directly attached to the second stage,” Argemí points out, adding that the thrust loads go directly to the stage, rather than through the gimbal and thrust mount first. “This interface ring could be more or less adaptable to be as ‘plug and play’ as possible because not every rocket has the same diameter,” he adds.
Stoke Space similarly arrived at an aerospike-like design for its Nova upper stage, which powered the first “hop” of the company’s Hopper 2 in September 2023. The design doesn’t adopt a continuous plug or toroidal shape, using a ring of around 30 thrust chambers around the perimeter of the full-size design. On Stoke’s design, exhaust from these chambers expands inward and downward along the actively cooled heat shield base, producing an altitude-compensating effect similar to an aerospike, without the need for the full plug.
While Pangea’s initial focus is on successfully sending the engines to orbit and validating their performance, the company is already testing the engine’s ability to also act as a heat shield for re-entry. From the outset, the design has accounted for many re-entry loads using computational fluid dynamics (CFD), simulations, and, more recently, tests in a supersonic wind tunnel.
Testing the 3D-printed combustion chamber and injection heads for the Arcos engine components in Germany in 2023. (Credit: Pangea Aerospace)
Because aerospikes adapt to ambient pressure, they are efficient at a wide range of altitudes. Argemí points out that the Arcos’ aerospike nozzle has a high expansion ratio of around 180:1. This would give very high performance in a vacuum, even more so than the Merlin vacuum engine, which has an expansion ratio of around 165:1. For comparison, a sea-level Merlin 1D would perform at around 16:1.
Pangea is targeting 360 seconds of specific impulse in vacuum — a standard measure of engine efficiency also known as ISP. This would compare favorably against the Falcon 9’s Merlin Vacuum engines, which are understood to have an ISP of 348. “Compared to the classical two-stage to orbit design, the more vacuum-optimized you want to be, the longer your vacuum nozzle. With our engines, you could get very compact and still retain all the performance.” Argemí adds.
He describes the aerospike as a performance generator rather than a thrust generator, emphasizing that on conventional two-stage orbital vehicles, the focus on the first stage is thrust. “You just want to cluster bell engines, and it’s way better because the thrust density — the amount of kilonewtons per square meter — is larger,” he explained.
The aerospike, by comparison, places thrust generation only around the engine’s perimeter, thus making a lower thrust density. This makes the engine more appropriate for a micro-launcher’s first stage but less so for larger vehicles, where Argemí notes it would be better to cluster more traditional bell engines and let the aerospike shine on the upper stage. “You could cluster aerospikes,” he adds, “but then the diameter of the full rocket would become gargantuous!”
Side view of Pangea’s October 2023 tests of the bi-material combustion chamber at DLR Lampoldshausen. (Credit: Pangea Aerospace)
A key design challenge with aerospikes is cooling them down. The throat of an aerospike is the large circumference, whereas on a traditional bell shape, it’s a far smaller circle, Argemí explained. The throat is where you have the largest heat flux, and combining this with a large diameter means that a high mass flow rate will be needed to actively cool the central plug.
Pangea’s solution to this thermal management is to implement a dual regenerative cooling system. “We’re using both propellants to cool it down because, historically, rocket engines are just cooled with fuel,” Argemí said. “Normally, you have way more oxidizer — which is not the best coolant in the world — but you have a lot, so let’s use it.” The Arcos inherited this learning from the P1 and cools several parts of the engine using both propellants.
Thermal management aside, another key challenge is to reduce the manufacturing cost of an aerospike engine to make it commercially attractive. Using 3D printing, the Demo P1 was constructed using just two parts. Scaling up to a commercial engine with several tonnes of thrust added manufacturing complications, however. Despite this, 60% to 70% of the Arcos engine still benefits from combining certain parts into single units.
Demo P1 engine during its testing campaign. (Credit: Pangea Aerospace)
“One of the advantages of the aerospike is [that] it’s so big but it’s hollow inside, so you have a lot of space where you put stuff,” Argemí explains. “In our case, all the engine control unit (ECU), the valves, and, of course, the power pack. It’s a conventional gas-generator cycle to start with. We have plans to close the cycle later on Arcos, but … one thing at a time – we already have several products ongoing in parallel!”
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For now, there are no plans to explore a different propellant mix, such as hydrogen and oxygen, which offers even greater performance, but also presents challenges.
One distinct advantage of aerospikes is that ground testing can serve as a good indicator of later performance in a vacuum, thereby saving the effort of shipping and testing it in a more expensive vacuum test facility. The real test, of course, will be onboard an upper stage while in flight.
“We’re targeting our first flight before the end of this decade,” Argemí announced as Pangea’s more conservative goal. He emphasized that the company hopes to move to an integrated test with an undisclosed client by the end of next year, with a first flight sometime after that on the roadmap.
The company continues to test the Arcos engine at the Lampoldshausen facility in Germany. Early testing in October 2023 verified the regeneratively cooled combustion chambers that were constructed using additive manufacturing to bond two different materials together — the first demonstration of its kind in Europe. It also tested two different 3D-printed single-piece injector heads designed for rapid reusability, easy inspection, and minimal refurbishment.
Pangea logo on the casing of the Demo P1 aerospike engine. (Credit: Pangea Aerospace)
“We do not currently have our own cryogenic test facilities,” Argemí explains. Pangea has its own infrastructure for other aspects of testing, and while such facilities can be expensive to build, it considers it a no-brainer for a propulsion company to eventually develop its own. Using the German DLR site enabled the company to more quickly conduct the month-long test campaign for its Demo P1 in the early days of development. The final test was intended to push the engine to destruction in order to discover its limits, but in a testament to its robust design, the engine outlasted the remaining propellant supply and survived.
Pangea is set on becoming the “go-to” company for a range of propulsion solutions, offering rocket and spacecraft developers an alternative to the cost and time required to design and build their own engines. To reinforce this, the company announced a rebranding from Pangea Aerospace to Pangea Propulsion on July 29. Its product range also covers in-space propulsion, with additional products suitable for cubesats, orbital transfer vehicles, or even landers.
Nereus, previously known as U-Nyx, will provide in-space mobility and began as a tiny thumb-sized one-newton engine for cubesats. This uses a more conventional bell nozzle, as there would not be enough mass flow rate to cool down an aerospike design, Argemí notes. The name, like its Nyx predecessor and other Pangea product lines, draws inspiration from the names of mythological creatures from that supercontinental era.
Nereus (previously U-Nyx) bipropellant cubesat thruster during testing, April 2023. (Credit: Pangea Aerospace)
The engine burns High-Test Peroxide (HTP), a concentrated form of hydrogen peroxide, and Jet 1A, a grade of aviation kerosene. Whereas other companies might use the more traditional hydrazine or even hall-effect thrusters, Pangea decided to capitalise on its expertise in liquid propellants. HTP has a very good performance and is scalable, Argemí notes, adding that the main desire was to remove the toxicity of hydrazine and align with the European Space Agency’s (ESA) desire to move its ecosystem away from it. While hydrazine is proven and well-known, teams are required to suit up to handle it, such as loading it into satellites, whereas using HTP will simplify ground operations and therefore reduce costs.
The company’s rebranding also introduced Cryox, a 30 kilonewton methalox engine for orbital missions based on the Arcos combustion chamber, which joins its engine family. Just over a year ago, Pangea was awarded several contracts to work with ESA and the French space agency, CNES, to begin the process of developing Europe’s first full-flow stage combustion engine. Kronos will be purpose-built for heavy and super-heavy launch vehicles, and similar to SpaceX’s Raptor engine when the project is finally realized.
Until then, Arcos continues its journey to disrupt our assumptions about reusable propulsion, combining high efficiency, reusability, and sustainability in one product. For its customers, this could mean ultimately more payload into orbit, with a simpler and less costly route to market.
(Lead image: Successful test of a bi-material combustion chamber with bio-methane and oxygen in Lampoldshausen, October 2023. Credit: Pangea Aerospace)
