A new type of engine combines the speed of rockets with the gas mileage of jets in a single package. Led by aerospace and mechanical engineer John Bossard, a team has built and tested a rocket engine of Bossard’s design that he calls a "turborocket."
The RTR turborocket could also be used in fast, high-flying drones and to further develop resuable rockets. The engine does away with the separate turbopump, combustion chamber, and nozzle of a conventional pump-fed, liquid-fuel rocket engine. Instead, all three are combined in a single structure that Bossard says makes the engine both simpler and more compact. It is the compact nature of the design that Bossard says ideally suits it for so-called combined cycle engines, that is engines that can be toggled between multiple modes of operation.
Bossard’s combined cycle design, which incorporates a turborocket and a turbojet, and which he calls the RTR turborocket or just RTR, could allow an aircraft to take off as a jet and switch to rocket power to fly faster than a jet could alone, and potentially right out of the atmosphere. "Simple also means lightweight, and we think the RTR could have an excellent thrust-to-weight ratio," says Bossard. "Maybe really excellent."
In the turborocket prototype that the team has built, fuel and oxidizer flow into a rotating, cylinder-shaped combustion chamber, where it is ignited. Exhaust gases exit a pair of nozzles built into the business end of the engine at a slight angle to the axis of rotation. The angle of the nozzles not only pushes the engine, as in a conventional rocket, but also starts the combustion chamber spinning. The resulting centrifugal force pumps fuel and oxidizer into the chamber at a higher pressure, serving the same function as the turbopump in a conventional design.
Bossard says that doing away with the extra gear and plumbing of a conventional rocket engine enables the new design to be integrated with a jet engine without having to make major changes to the jet Both rocket and jet can use the same fuel.
Beyond their first possible use in drones, team member John Bergmans, a consulting mechanical engineer in the NewSpace industry, sees the RTR turborocket as the next step in the development of reusable rockets. SpaceX and Blue Origin, he points out, have taken an important step toward more affordable spaceflight by bringing rockets back to Earth intact for refueling and reuse. But it is only the first step, he says.
"In the short term, this approach will provide a competitive advantage to firms that can master this technique. However, this advantage will be quickly eroded once this method becomes commonplace in the industry. We think the time is now to be laying the groundwork for the next step change in launch costs."