China Paper Faults the Single-Engine Risk in NASA's Moon Lander

One engine, or four? The answer decides whether a lunar crew has a way home if something fails during the most dangerous minutes of a Moon mission, and a Chinese research team has turned that question into a pointed critique of NASA's Artemis program.

A peer-reviewed paper published in March in the journal Chinese Space Science and Technology argues that the American lunar architecture contains some glaring weaknesses. The assessment drew fresh attention this week after the South China Morning Post detailed it on Friday, framing the engine question as a measure of how much each space power is willing to pay to protect human life.

NASA's design leans hard on a single, powerful main engine. On the way down, that one engine controls the entire descent from lunar orbit to the surface. On the way up, the same single engine is the only ticket back to orbit. If it quits, there is no backup. The lineage runs straight back to the Apollo Lunar Module of the 1960s, and it survives in the Orion spacecraft flying today.

China's proposed lander makes the opposite bet. Developed by a Shanghai-based national laboratory team, it uses four variable-thrust engines that together produce more than 30 kilonewtons, according to Interesting Engineering's account of the paper. Lose one engine entirely, the researchers say, and the remaining three still deliver thrust comparable to the main engine on NASA's Orion. Six smaller orbit-control thrusters sit underneath as a further layer, able to fire from the surface for a rough ascent if the mains go dark.

Redundancy is cheap to want and expensive to carry

So why doesn't everyone bolt on spare engines? Mass. Every extra engine adds weight, and weight is the currency a lunar mission can least afford. That trade-off is the real subject of the paper, and the Chinese team's answer is a piece of plumbing: a common bulkhead tank, sometimes called a "common bottom," where fuel and oxidizer share a single wall instead of sitting in two separate tanks.

The shared-wall design strips out duplicated structure. The researchers put the saving at the "hundred-kilogram level," with a composite build that comes in more than 20 percent lighter than a metal equivalent. The tank also doubles as a load-bearing part of the vehicle's frame. In full-system hot-fire tests, the team reported, the four engines stayed coordinated tightly enough to hold thrust variation under 100 newtons, the kind of precision needed to keep a lander from tumbling on the way down.

The timing sharpens the point. China has been merging its lunar programs and pushing toward a crewed landing of its own, and a paper that spotlights a safety gap in the rival effort reads as much like strategic positioning as pure engineering. NASA, for its part, has spent the Artemis era defending a heavier, costlier architecture against precisely this kind of redundancy argument.

A caveat worth keeping in view: this is one country's engineers grading a rival's homework, in a peer-reviewed journal but in the middle of a sharpening US-China race to the Moon. It is an argument, not an admission from NASA, which has not responded to the critique and whose single-engine approach has flown crews before. Redundancy also is never free, a point the paper concedes by spending most of its length solving the mass penalty its own four-engine layout creates. NASA lays out the broader plan on its Artemis program page.

The contrast becomes concrete as NASA works toward Artemis III, the first crewed landing of the program. Strip away the geopolitics and the dispute is an engineering value judgment: how much mass, money and margin a program is willing to spend so that the trip back is never riding on a single engine.