"In the moon landing competition of the 21st century, engineers must answer a question: What will happen if the main engine fails?"
As the Sino-American lunar landing program continues to draw attention, Hong Kong's English media outlet The South China Morning Post noted on June 13 that a recent paper published by a Chinese research team revealed differences in the safety design of the Sino-American manned lunar landing plans. Since the Apollo era, American deep-space probes have always favored a single main engine design, which means that both the descent and ascent phases rely on a single main engine. If this engine fails, there is no backup mechanism, "exposing some significant drawbacks." In contrast, the Chinese design, which uses "four variable-thrust main engines + multiple redundancies," effectively reduces safety risks.
Reports describe that the traditional American single-engine architecture and China's multi-redundancy design may reflect different perceptions of the value of human life by both sides.
NASA’s manned lunar orbiting mission enters final stages. IC Photo
The report indicates that, from the Apollo lunar module of the 1960s to the new-generation Orion spacecraft developed by NASA for the Artemis program, American spacecraft have long relied on a single high-thrust main engine to complete critical tasks.
During the descent phase, one main engine is responsible for controlling the entire process of landing from the lunar orbit to the surface of the moon. During the ascent phase, one main engine is the only guarantee for returning to the orbit and making the journey back home.
Once this engine fails, there is no alternative plan.
A peer-reviewed paper published in the journal China Space Science and Technology in March this year pointed out that, overall, foreign large-scale deep-space probes have some significant drawbacks, including poor utilization of structural layout, lack of redundancy in main engines, and complex system design.
The paper states that in the face of prominent shortcomings in the design of manned lunar exploration vehicles abroad, China’s manned lunar exploration vehicles have achieved the following innovations and technological breakthroughs. First, the redundancy backup of the main engine ensures the reliable safety of the vehicle. The propulsion system is designed to ensure consistent operating conditions of all engines. Second, the use of common base tanks improves the structural utilization rate, and a pressurized system that ensures reliable safety has been developed for these common base tanks.
Chart: A chart to help you understand “Mengzhou” and “Lan Yue” IC Photo.
The South China Morning Post analyzed that China's reliance on four engines rather than one means that if one of them fails, the remaining three can still provide thrust comparable to that of the entire main engine of the Orion spacecraft. Moreover, the safety measures are more than just a single layer of protection. Even if the main propulsion system is severely damaged, the lunar module is equipped with six smaller orbital control engines, which can be ignited on the moon to assist in rapid ascent.
Public information shows that China's lunar landing vehicle has a total mass of approximately 26 tons, consisting of a lunar module and a propulsion module. The engine module of the lunar module includes four 7500N main thrust engines and several attitude control engines. All functional modules of the propulsion system are designed with primary and backup redundancy, so that any failure in one component can be reconfigured to ensure safety. In emergency mode, two main engines along with smaller attitude control engines can be used to assist in lunar takeoff.
The report also mentioned that if four engines are safer than one, then why doesn't everyone do the same?
The answer is weight.
More engines mean greater quality. The Chinese team solved this problem through a structural genius design—the shared bottom storage compartment.
In manned deep-space vehicles that use a pressurization propulsion system, China has for the first time adopted a storage tank design that allows oxidants and fuel to share the same barrier. In contrast, all previous designs used two separate storage tanks, which meant doubling the structural weight and reducing usable space.
The propulsion system of the Chinese lunar module uses a propellant composed of methylhydrazine and nitrogen tetroxide. It is equipped with 4 ellipsoidal common fuel tanks, each with a capacity of over 5000 liters. These tanks can be filled with an additional 6 tons of propellant. The pressure difference between the fuel tanks is reliably maintained at 0.15 to 0.23 MPa.
By allowing both propellants to share a separator, this design eliminates structural redundancy in the storage tank itself. Researchers say this can save up to ‘hundreds of kilograms’ in weight.
The saved weight makes it possible to install four engines instead of one. Using composite materials, this type of storage tank reduces weight by more than 20% compared to traditional metal structures.
This structure can also bear loads, becoming part of the spacecraft framework, thereby further optimizing the overall weight of the device.
The paper presents data obtained from the full-system hot run. It was proven that they were able to synchronize the four variable-thrust engines so that the thrust deviation was less than 100 N, thereby ensuring that the lander would not experience fatal rolling due to thrust imbalance.
Test results also show that the high-risk common base storage tank pressure control issues have been effectively resolved.
If other countries want to replicate this "four-engine + common base tank" solution, they must master the ability to independently control the pressure of the common base tank under extremely tight safety margins.
At the same time, it is necessary to achieve consistent thrust synchronization among multiple engines with adjustable thrust. As the number of engines increases, the complexity of this problem will increase exponentially.
It is worth mentioning that NASA's manned lunar landing system (HLS) has selected two commercial solutions for its project. These include SpaceX's "Starship" HLS and Blue Origin's "Blue Moon" manned version. NASA has opted for a multi-rocket cluster layout for its HLS, which differs from the traditional Apollo architecture.
However, both of these types of landers are still some time away from being ready for mission. The former is still awaiting completion of on-orbit refueling and comprehensive verification, while the latter is still in the development and testing phase.
Developed by SpaceX, the "Star Ship" HLS is a massive stainless steel aircraft that can reach a height of up to 50 meters. It is planned to carry out lunar landing missions. Although this idea is ambitious, many experienced aerospace experts are concerned that such high-altitude aircrafts face extremely complex physical challenges during lunar landings, which means that the crew will face significant risks.
The United States' "Artemis Program" has previously encountered concerning issues during human flight tests, including nitrogen leaks and damage to the heat shield protection layer. These problems could be fatal, which is increasing the pressure for the United States to return to the moon before China does.
The South China Morning Post has contacted NASA for a response.
And China's manned lunar landing program is progressing in an orderly manner. By early 2026, the development of major flight products such as the Long March 10 rocket, the Dream Ship manned spacecraft, and the Lunar Landing Vehicle has been progressing smoothly. Numerous major tests have been completed, including the zero-altitude escape of the Dream Ship manned spacecraft, the landing and takeoff of the Lunar Landing Vehicle, the rigging ignition of the Long March 10 rocket, the low-altitude demonstration and verification of the Long March 10 rocket system, and the flight with maximum dynamic pressure of the Dream Ship manned spacecraft system. The Lunar Landing Vehicle completed its main tasks during the prototype stage in October 2025.
Our country plans to achieve manned lunar landings by 2030. In the future, we also plan to develop lunar mobile laboratories with extensive mobility capabilities, and ultimately establish lunar research stations with long-term presence.
