A column about curious stories from the worlds of science and technology. Today: an engine a toy model predicted, and academic science refused to notice for twenty years. On November 2, Swiss startup Stellar Alpina unveiled the Morpho lunar lander and the Monarch orbital tug—European vehicles powered by a Rotating Detonation Rocket Engine, a detonation propulsion system that spent nearly ninety years classified as a defect, then forty as a laboratory curiosity, and now is vying to become transport for the lunar economy. A story involving two drinks, a Catholic calendar, and a vacuum-cleaner motor.
Let’s start with the news, so we can talk about its genetics afterward. Stellar Alpina of Dübendorf—a company just nine months old, its four co-founders coming out of the student organization ARIS—revealed the design of two vehicles. Monarch: 1,000 kilograms of launch mass, 200 kilograms of payload, and six kilometers per second of total delta-v—two to four times more than conventional hydrazine tugs. Enough to climb from low orbit to geostationary orbit (3900–4200 m/s) or fly to the Moon (3100–3200 m/s), all in one package. The business model is called mobility-as-a-service: you pay for expended delta-v, like a taxi meter. The second vehicle, Morpho, is a lander carrying fifty kilograms down to the lunar surface, and its niche is described honestly: Europe has no equivalent of NASA’s CLPS program, ESA is building its large Argonaut, and nobody is offering small, flexible commercial missions. Co-founder Victor Ellisen calls the lander “transport infrastructure for a thriving lunar economy”—sounds like an investor slide, but there is hardware behind the slide: the Genziana engine, running on propane and hydrogen peroxide, 1–5 kN of thrust, 150 hot-fire tests across twenty-three chamber configurations in six months. Monarch’s orbital debut is planned for 2029.
Now, honestly about the competition: in April this year, American company Astrobotic ran its own RDRE, “Chakram,” for 300 uninterrupted seconds at NASA Marshall—a current duration record, more than 470 cumulative seconds across two prototypes, with thrust above 4,000 pounds. Neither Astrobotic nor Stellar Alpina has yet flown its detonation propulsion system in space. So the story below is not about who won. It is about why a wave regarded as a flaw for a century suddenly became a marketing headline.
Detonation and deflagration are two ways of burning fuel, and anyone who has drunk soda and champagne from the same bottle knows the difference... no, better this way: deflagration is combustion—the flame front creeps through the mixture slower than sound, pressure has time to equalize, the chamber breathes evenly. Detonation is when the front races through the mixture at supersonic speed: the shock wave itself compresses fresh fuel thousands of times faster than it can “realize” it has ignited, and lights it with a single blow. The difference is not speed for speed’s sake, but thermodynamics: deflagration burns at constant pressure, detonation at nearly constant volume, and it is the only combustion regime in which pressure at the chamber exit is HIGHER than at the inlet. Every other engine humanity has made, from a camping stove to Ariane 6, spends part of its combustion energy simply maintaining pressure in the chamber. Detonation abolishes that line item.
The price of elegance is heat and obstinacy. The detonation front is hotter than 2,000 degrees and races around the ring at more than a kilometer per second—the chamber for such a regime must be both furnace and anvil. Ellisen owns the standard RDRE test-stand joke: the main task is “not letting the engine melt itself.” That is why Stellar Alpina’s next vehicle will have water cooling, while Astrobotic is printing chambers with controlled wall porosity: fuel seeps through the metal and carries away heat before it burns.
Now—the scene this whole thing was built around. In 1926, English chemists Campbell and Woodhead burned carbon monoxide with oxygen in a long glass tube and filmed a classic detonation. On the developed footage appeared an uninvited guest: a bright spot that, for some reason, ran not straight but in a spiral along the wall, like a bead on an invisible thread, trailing a tail of glow behind it. The rotation frequency depended on the tube’s diameter—to the point that if you inserted a coaxial rod inside, the frequency changed while the detonation’s speed itself did not. The authors honestly recorded the artifact, could not explain it, and apparently did not worry much about it: experimental rigor over interpretation.
Science’s next reaction was pure skepticism: “that cannot be, because it cannot be at all.” The Chapman–Jouguet detonation theory described a smooth one-dimensional front—one velocity, one structure, no spirals. The spiral was stubbornly measured for another two decades, while the explanation came not from “serious” mechanicians but from acoustics: Manson in 1946 and Fay in 1952 realized that the “tail” behind the spiral head was a transverse acoustic wave, a resonant mode of gas in a tube, a close relative of an organ pipe and a bottle humming at the edge of a table. That was only the beginning: it still remained to believe that sound might not merely accompany detonation, but be a constructive part of it.
And now the best part: how long academic science refused to believe its own eyes. In 1940, twenty-six-year-old Yakov Zeldovich published an article in the Journal of Technical Physics with the unassuming title “On the Energetic Use of Detonation Combustion.” It contained an honest thermodynamic calculation: a cycle using detonation combustion of fuel delivers higher efficiency than a constant-volume combustion cycle—using ethylene with air, it came to around thirteen percent. The same article also carefully explained where detonation brings NO advantages: in a steady air-breathing engine, by Zeldovich’s own calculations, it cuts thrust in half compared to an ideal ramjet. So one of the fathers of the Soviet hydrogen bomb and the author of a model for detonation-front structure calculated it all—and honestly pointed out where the gain existed and where it did not.
What happened afterward was recounted in 2006 by Elaine Wintenberger and Joseph Shepherd of Caltech: the article remained virtually unknown in the West until its translation in the Journal of Propulsion and Power—a translation they arranged. Six decades—through the hydrogen bomb, satellites, and Apollo—Western engineers “rediscovered” calculations that had been sitting in bibliographies a couple of lines away from their own work all that time. Neither denial nor triumph—a quiet gap in the bibliography that cost decades.
The irony has a second layer: even once read in English, Zeldovich’s “seed” was considered thermodynamic perfectionism for decades. A tantalizing ten to twenty-five percent on paper, but in hardware—an unstable wave that goes out at a sneeze, plus heat fluxes that melt any reasonable chamber. Peer-reviewed estimates for liquid bipropellant systems are more modest than the slogans: from three to fourteen percent added specific impulse, more for hydrogen systems. Not a revolution, but for an orbital tug, where every percent of fuel means kilograms of payload, that is very much money.
Meanwhile, in Novosibirsk, the thing from which the whole modern RDRE world grew was taking place. In 1957, Boris Voitsekhovsky was studying spin structure: to examine a “head” racing at around two kilometers per second required exposures shorter than a microsecond—industrial photographic recorders could not handle it. So he built the camera himself: a transparent drum spun by an electric motor from a household vacuum cleaner, an f/1.5 aperture, and—the main trick—he tilted the drum’s axis relative to the tube’s axis so that the film’s linear speed exactly compensated for the movement of the head’s image. The result was the first clean photographs of spin structure, and the February 1957 paper “On Spin Detonation” introduced the very concept of the transverse wave—without which modern detonation theory does not exist.
And in 1959 Voitsekhovsky achieved the crucial thing: continuous spinning detonation in an annular chamber—the wave runs around the circumference endlessly, fresh mixture is fed radially, and the wave travels perpendicular to the primary flow. It is literally the blueprint for today’s RDRE: not pulsed flashes requiring the chamber to be purged after each one, as in a pulse detonation engine, but a continuous rotating process that self-feeds. As a bonus, he noticed a detail few paid attention to: heat flux into the walls during continuous detonation proved noticeably lower than during ordinary combustion of the same mixture—apparently because the wave runs past a point instead of roasting it forever. After that, the Lavrentyev Institute of Hydrodynamics—Bykovsky, Mitrofanov, Zhdan, and colleagues—brought the regimes to rocket and ramjet chambers using dozens of propellants, and from 1975 to this day, the field has been held up largely by this Novosibirsk school.
A parallel global timeline, for scale: the first flight of a rocket using a liquid RDRE—Warsaw, September 2021, three seconds of operation and 450 meters of altitude; the first RDRE flight into space at all—JAXA in July 2021, a 500-newton engine on the second stage of an S-520 sounding rocket, specific impulse of 290 seconds; NASA in 2022 ran its 3D-printed RDRE on GRCop-42 for nearly a minute at full thrust with a chamber pressure of 622 psi, by December 2023 brought it to 251 seconds and 5,800 pounds of thrust, and stated its goals frankly: lunar landers, upper stages, and supersonic retropropulsion for landing on Mars. GE Aerospace is running detonation as part of a hybrid turbine for hypersonics, DARPA and RTX are building the Gambit missile, while GE and Lockheed Martin announced an RDE-powered hypersonic missile in 2026. A dull list of those already voting with their wallets for a wave that in the 1930s was considered interference on film.
November 2 in this chronology is not a scientific turning point, but an economic one. Stellar Alpina does not claim to have invented anything: Engine 0 retraced the path of ARIS PEGASUS, which in 2024 built the world’s first student liquid-bipropellant RDRE (liquid propane plus liquid oxygen—the seventh country to ignite a detonation wave). What it claims is mundane, practical integration: storing peroxide and propane at room temperature—no liquid hydrogen, no cryogenic infrastructure, no toxic hydrazine diplomacy; the wave itself creates chamber pressure, so there is no need for either high-pressure pressurization or a turbopump driven by a cryogenic pair. By the company’s own estimate, all this currently stands at TRL 4 out of 9—“validated in a relevant environment,” meaning on a test stand, not in flight. Humanity measures the distance from a test stand to the Moon not in kilometers but in decades: it is worth remembering that sixty years ago, continuous detonation too was “just a laboratory.”
And the final punchline, which is why this story is worth telling. Every link in this chain was initially dismissed as trash: the spiral artifact on film—a defect in the experiment; detonation efficiency—“too good to be true”; Zeldovich’s article—untranslated and therefore nonexistent; the wave in a ring—student exotica from Novosibirsk. A Swiss startup with a pre-seed round of 3.5 million Swiss francs is selling all of it as transport to the Moon. Science, as usual, was in no hurry—only engineering hurries: nearly a hundred years passed from a spiral on a photographic plate to the first commercial price list for delta-v. If Morpho ever lands on the Moon, a wave will be spinning in its chamber—the wave they wrote off as a recording defect in 1926.