Can a detonating rocket engine redefine global flight? Venus Aerospace
During hypersonic flight, an aircraft or missile flies at Mach 5 and above. That’s five times the speed of sound, or approximately 6,173 km/h (3,836 mph). At those speeds, passengers could fly anywhere on Earth in under four hours.
Today, hypersonic flight is the realm of spacecraft and advanced weapons systems. Companies such as Boom Supersonic and Otto Aviation are making strides to enable commercial supersonic and transonic flight. However, one company, Venus Aerospace, aims to unlock a new era of hypersonic aviation.
In an interview with Interesting Engineering, Venus Aerospace CEO Sassie Duggleby provided an update on the company’s latest flight test. She believes hypersonic flight will “collapse global distances,” allowing passengers to fly across the globe and back in a day.
Venus Aerospace’s Rotating Detonation Rocket Engine (RDRE). Source: Venus Aerospace
The technology making this possible is Venus Aerospace’s rotating detonation rocket engine (RDRE) and its VDR2 air-breathing detonation ramjet. While RDREs could power highly efficient spacecraft to the Moon and Mars, Venus Aerospace believes combining them with ramjet technology will enable its Stargazer M4 – the world’s first hypersonic airliner.
A brief history of the RDRE
The idea for a rotating detonation rocket engine emerged in the 1950s. Soviet scientist Bogdan Voitsekhovsky’s research into detonation-based propulsion served as an early indication that the technology was possible.
Early theoretical work in the Soviet Union and the US focused on harnessing the rapid energy release of detonations. These detonations burn fuel more efficiently than the deflagration used in conventional chemical rocket engines.
Research was slow until the 1990s, when computational modeling and material science advances enabled practical exploration. In the 2000s, engineers in the US and Russia began experimenting with RDE designs. By 2010, US Air Force and NASA-funded tests had demonstrated stable detonation waves in annular chambers.
In recent years, companies like Venus Aerospace and research institutions like Purdue University have achieved key milestones. In 2023, NASA fired up a 3D-printed RDRE for a 251-second test fire. The engine produced 5,800 lbs of thrust. In a statement released after the test, NASA noted that it worked with Venus Aerospace to scale the technology.
“The RDRE enables a huge leap in design efficiency,” said NASA engineer Thomas Teasley, who leads the RDRE test effort. “It demonstrates we are closer to making lightweight propulsion systems that will allow us to send more mass and payload further into deep space, a critical component to NASA’s Moon to Mars vision.”
In May this year, Houston-based startup Venus Aerospace claimed it made history by completing the first-ever flight test of a rotating detonation rocket engine (RDRE) in the US. During the test on May 14, Venus launched a small rocket featuring its RDRE from Spaceport America in New Mexico. The company explained that it is now a “step closer to making high-speed flight accessible, affordable and sustainable.”
How rotating detonation rocket engines work
Unlike conventional rocket engines, which continuously burn fuel in a combustion chamber, RDREs harness the power of a detonation wave that travels around a ring-shaped, or annular, chamber.
A fuel and oxidizer mixture is piped into a gap between two coaxial cylinders. Detonation then produces a supersonic shockwave that speeds around the annular chamber, generating more heat and pressure.
“RDREs offer a step-change in propulsion efficiency by using detonation waves – rather than deflagration – to generate thrust,” Duggleby explained to IE over email. “This allows for a higher thrust-to-weight ratio in a smaller, more fuel-efficient footprint compared to traditional rocket engines.”
Scientists theorize that RDREs could be 15-25 percent more efficient than conventional rocket engines. For the Venus Aerospace team, this efficiency is crucial for enabling hypersonic airliners. Duggleby explained that ” compactness and power density are key to enabling hypersonic aircraft to take off from conventional runways – eliminating the need for long runways or specialized launch systems.”
A diagram of Venus Aerospace’s VDR2 engine. Source: Venus Aerospace
To make this possible, Venus is also developing its VDR2 engine, which combines RDRE technology with an air-breathing ramjet. Typically, rocket engines boost hypersonic vehicles to high altitudes. They glide down to lower altitudes before accelerating to Mach 5. The VDR2 engine can transition between RDRE and ramjet flight modes to remove the need to boost to such a high altitude.
“In Venus’s design, the RDRE works in tandem with our air-breathing ramjet to create a single-engine system that can operate from takeoff through hypersonic cruise,” Duggleby continued. “We’re building an aircraft that functions within today’s aviation infrastructure but performs at tomorrow’s speeds. And notably, Venus is the first company to successfully flight-test a high-thrust RDRE – a critical milestone on the path to practical hypersonic flight.”
To be precise, Venus’ VDR2 will feature an RDRE behind the nose cone. This RDRE shares a compact integrated nozzle system with an air-breathing ramjet. This allows the engine to transition between propulsion modes smoothly.
Once in flight, the ramjet leverages the aircraft’s forward velocity to compress air, enabling efficient cruising at Mach 4–6 without rocket boosters. RDREs and ramjets require fewer moving parts than conventional engines, simplifying maintenance and lowering weight and cost.
Beyond Venus’ world-first RDRE flight test
At the rear of Venus Aerospace’s VDR2 engine, a high-thrust RDRE will deliver primary thrust for takeoff and acceleration. Following its flight test on May 14, Venus Aerospace claims it is the first US company to have flown a high-thrust RDRE.
“This was the first known US flight of a high-thrust RDRE, and one of the first in the world to demonstrate in-air performance,” Duggleby said. “The RDRE ignited successfully on the rail and powered a 3-5 second vertical ascent, reaching roughly 4,400 feet with a peak acceleration of 4 Gs.”
According to Duggleby, the test validated ignition, integration, and recovery of a compact, efficient RDRE. Essentially, it brought “detonation-based propulsion out of the lab and into the real world,” she said. Moreover, “the engine was recovered nearly intact – a remarkable outcome for a first-in-kind rocket flight.”
The company will now pore over the data. Duggleby says the team is “still analyzing the telemetry, but the results are extremely promising.” Next, they want to perform more flight tests further to validate their RDRE and VDR2 technologies.
“Our next major milestone is a 2000-lbf thrust-class RDRE demonstration, targeting Mach 2–3 conditions and higher-performance validation,” Duggleby continued. “This test will scale up our engine architecture and demonstrate greater energy density, thermal resilience, and aerodynamic performance.”
“We’re also advancing toward flight testing of our detonation-based ramjet (VDR2), which, when integrated with the RDRE, will enable runway-to-hypersonic propulsion,” she said. “That unified system is the foundation of Stargazer, and every step we take now prepares for that future.”
How will hypersonic flight change the way we travel?
Last year in December, Venus achieved first ignition of its VDR2 engine during a hot fire test. The company explained it had “demonstrated the exceptional ability to start a ramjet at takeoff speed, which is revolutionary. Typically, ramjets cannot start until Mach 3.5.”
The vehicle that could one day help make Venus’ hypersonic aviation vision a reality is the Stargazer M4. If all goes to plan, that aircraft will fly at cruise speeds of Mach 4 and will be capable of a top speed of Mach 9.
An artist’s impression of the Stargazer M4 in flight. Source: Venus Aerospace
With the Stargazer M4, Venus Aerospace presents a rousing vision of a future where commercial hypersonic flight is a reality. Flying at those speeds, passengers could fly anywhere on Earth, meaning they could take a day trip anywhere.
“Hypersonic flight will collapse global distances,” Duggleby said. “Imagine being able to fly from Los Angeles to Tokyo in under two hours—and be home for dinner. It will reshape business, logistics, national defense, and even personal relationships.”
While Venus Aerospace could revolutionize commercial air travel, its technology would likely take a long time to benefit the average air traveler. Duggleby states, “Early use may skew toward high-end commercial or defense applications.” However, “the design intent is to build toward broader accessibility over time.” The company believes it will deliver the Stargazer M4 by the late 2030s.
Beyond the cost to future flyers, hypersonic airliners could also have a significant environmental impact. Guy Gratton, associate professor of aviation and the environment at Cranfield University in Bedfordshire, believes companies and research institutions should focus on low-emission flight—hydrogen propulsion technology and ‘Blended Wing Bodies’—rather than speed and convenience.
“As an aeronautical engineer, I find the possibilities of [hypersonic] aircraft incredibly exciting,” Gratton told IE. “But in a world where teleconferencing is commonplace and emissions are increasingly of concern, it’s hard to see the real justification.”
“It’s worth asking whether the enormous cost and technical challenge of commercial hypersonic flight is worth it. This will be extremely expensive, and the energy use, and thus emissions, will be far greater than current and conventional aeroplanes,” Gratton continued.
Like Boom Supersonic, Venus Aerospace aims to fly its aircraft using sustainable fuels. The company has used a sustainable aviation fuel (SAF) developed by CleanJoule to power its RDRE during engine tests. CleanJoule’s Space SAF is a drop-in replacement for super-refined kerosene fuels used in liquid rockets. It is derived from feedstocks and reportedly delivers a 4 percent improvement in energy density compared to petroleum-derived fuels.
As Duggleby points out, “Venus’s system is being designed to work with existing runways, integrate sustainable fuels, and radically simplify propulsion. Hypersonic travel could be cost-effective and scalable—not just fast, but accessible.”
Gratton isn’t quite convinced. He believes a great deal of work is required, and the environmental impact of these technologies will go beyond that of today’s commercial airliners.
“Companies like Boom Supersonic are doing impressive work in eliminating the sonic boom at Mach Numbers under 2, but that’s quite a different environment—and even there it’s likely to have significantly greater greenhouse gas emissions per passenger mile than most of what we’re presently flying,” he explained.
Flying anywhere on the planet in two hours is an undeniably tantalizing prospect. However, given the challenges our civilization faces today, should we be looking to slow down instead of pursuing speed no matter the cost?