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China’s first reusable rocket engine conducted ground tests before completing a recent test flight. Photo: Xian Aerospace Propulsion Institute

China’s reusable rocket engine tech ‘at practical stage’ after second test flight

  • It was recently put to the test in a launch – the first time China had reused a rocket engine, according to its developer
  • The engine can be used for vertical take-off and landing and is similar to those used by SpaceX on its Falcon 9 rockets
China has conducted a second test flight of a reusable rocket engine, similar to those used by SpaceX, closing a technology gap with the United States on low-cost space flight.

The liquid oxygen and kerosene rocket engine was recently put to the test in a launch and returned to Earth safely, the Xian Aerospace Propulsion Institute said in a statement posted on its WeChat social media account on Tuesday.

No further details of the flight were given, but the institute said it was the first time China had reused a rocket engine. The institute is a subsidiary of the state-run China Aerospace Science and Technology Corporation.

The engine is seen here in action. Photo: Xian Aerospace Propulsion Institute

The engine was first used as the main power system for a launch in 2021, and following inspection and maintenance after its return it was reassembled for the latest flight.

“This successful verification means that our engine reuse technology has entered the practical stage. That enables us to pay more attention to the high reliability, low cost and high performance of the engine,” Zhang Xiaojun, head of the institute, was quoted as saying in a China News Service report on Wednesday.

China has played a leading role in developing air-breathing engines for hypersonic flight but had lagged behind on reusable rockets using traditional engine technology.

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Liquid oxygen and kerosene rocket engines provide a main power source for space travel. Carrying their own oxygen they can function either in the air or a vacuum. They also have an advantage on thrust, the fuel is non-toxic and they create little pollution.

The Chinese engine can be used for vertical take-off and landing – the technology is similar to the Merlin-1D engine used by SpaceX on its Falcon 9 rockets.

The Xian institute said in the statement that scientists working on the engine had to overcome technical challenges at every flight stage – the first being the repeat ignition technology needed for vertical landing.

Before a second ignition, the engine needs to cool and purge the tank to clear away combustion and residual fuel from the first flight – a process that can differ according to the flight mode.

The institute said it had achieved three uninterrupted ignitions during ground testing and found a method to purge and pre-cool the tank.

The liquid oxygen and kerosene rocket engine was first used in a launch last year. Photo: Handout

The landing process is also challenging – during the return flight, the vehicle becomes lighter due to the gradual reduction of the remaining propellant.

A range of ways to adjust the engine’s thrust are needed to achieve controlled deceleration, or a soft landing. The institute said this was also part of ground testing and an earlier test with a Long March 8 rocket.

With repeat use and ignition, the engine also needs to be protected against impact and heat, as outside air pressure changes in the return stage. That means sealing materials are important, and the institute said its protective measures had proven effective during the second test flight.

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A plan to assess the reliability of the engine when it is being reused is also important. The institute said it had developed and adapted online real-time technology to evaluate the engine after a mission, providing a low-cost, fast way to carry out inspection and maintenance.

“The progress China has made in repeatedly using the liquid oxygen and kerosene engine is of great significance,” Zhang told China News Service.

He said the second test flight had provided “valuable experience and paved way for the subsequent development of a larger thrust reusable liquid oxygen and kerosene engine in China”.

“That will be a big leap from ground zero,” he added.