China Plans to Catch a Rocket with a Tether
China Plans to Catch a Rocket with a Tether
An overview of China's "other" Lunar super-rocket
China’s space program is known for its methodological approach, with plans set out years in advance. The appearance of a new unnamed rocket, at the Zhuhai airshow, however, suggests that these plans have been upended by reusable rocket technology. To shed some light on this unnamed rocket, I dived into the Chinese internet. What I learned is that China is gearing up to put its own spin on rocket reuse.
Background
China’s manned space program, called Project 921, has launched relatively few times, but each mission has been hyper-focused on achieving significant goals. These goals have largely stayed the same since the early 1990s: launch a crewed spacecraft, build experience in space, and follow it up with a permanent crewed space station by 2020.
China nearly nailed that timeline. The first crewed mission, Shenzhou 5, launched successfully in 2003, taking a single astronaut to orbit. It was followed by Shenzhou 6, 7, and 8, which replicated the entire American Mercury/Gemini programs, demonstrating multi-crew launches, a spacewalk, and rendezvous/docking capabilities. Since then, China has launched two small single-module space labs that have tested longer-duration missions, automated refueling, and automated resupply.
This has culminated in the soon-to-be-completed Tiangong Space Station (天宫空间站), a multi-module space station like the US-led ISS. With the completion of the TSS, however, the question becomes, what is next? The appearance of this new rocket suggests that China is setting its sights on the Moon.
The Moon
A crewed lunar program, notably, does not have official support from Beijing. Nonetheless, China's space program is actively developing and testing much of the hardware required for deep space flight, including a brand new reusable (and also unnamed) spacecraft, and a super-heavy lift rocket called the Long March 9 (LM-9).
The crew capsule has already test flown and will come in two flavors, a 14-ton version for operation in Earth orbit, and a ~22-ton version for beyond Earth orbit. China’s most powerful rocket, the capable LM-5, introduced in 2019, is unable to send such a craft to the Moon.
China has long toyed with a Saturn V/SLS-style Super Heavy Lift Launch Vehicle called the LM-9. However, as I detailed here, the LM-9’s future is in question as the design has seen tremendous revisions in the last few years. I speculate that engineers have tossed out the original specifications in favor of pursuing a Starship-like reusable rocket, thus delaying its introduction to ~2035.
Among the uncertainty surrounding the LM-9, the above model appeared at a Chinese aerospace show in ~2018. This rocket, which is unnamed but often nicknamed the ‘921’ rocket, honoring China’s manned space program, appeared with little explanation. For a country that has stuck methodically to its plan for 30 years, the appearance of this model is notably uncharacteristic.
After all, the LM-5, 6, and 7 series rockets are almost brand new. Additionally, with the LM-9 under development, what purpose could this new rocket have? Was the LM-9 canceled or will the 921 rocket supplement it? Is it just a concept? Are they both just concepts? We now have some answers.
The ‘921’ is Not a Paper Rocket
From the sparse reporting available, development on the ‘921’ began in 2017. It will come in two flavors, a single-core version to take the next-generation spacecraft/cargo to the TSS and a triple-core version for greatly enhanced launch capability.
The central core can be up to three stages and stand nearly 90 meters tall. Per recently released specifications, the single-core variant will be capable of lofting 18 tons to LEO and will replace the LM-2F, China’s only human-rated rocket, by 2030. Conceivably, it could also replace the LM-2, 3, and 7 series as well.
The triple core variant is designed to send ~27 tons to the Moon, similar to the SLS Block 1, making it a super-heavy lift rocket. With 27 tons TLI capacity, the 921 is capable of tossing China’s new 22-ton crewed spacecraft to the Moon, and possibly replacing the LM-5 series as well.
According to Zhou Yanfei, deputy chief designer of China’s Manned Space Program, the 921 will be based on LM-5 heritage components, utilizing improved versions of the 5-meter core structure, as well as YF-100 and YF-75D engines. This seems likely a means of expediting the development of the rocket.
Each core is powered by seven of the recently tested YF-100K engines, upgraded versions of the staged-combustion YF-100. The upper stage will be powered by the vacuum variant of the YF-100, the YF-100M, and the optional third stage will utilize the existing YF-75D hydrolox engine.
Photos found online show complete thrust structures already in fit testing, and a first flight is expected as soon as 2026. In sum, the hardware is largely functional, the 921 is not a paper rocket or a concept.
Reusability
I initially speculated that the rocket may be reusable, because like Blue Origin’s New Glenn and SpaceX’s Falcon 9, the rocket features a large number of engines with a single center engine for propulsive landing. China is separately developing reuse technology on the LM-8 rocket, which should attempt landing in the coming months.
We now have confirmation that the 921 will be reusable, albeit by 2032. Like Falcon 9, it will feature propulsive landing with restartable YF-100N engines. The YF-100N is a reusable version of the YF-100K, designed to fly up to ten times. Also like Falcon 9, it will use grid fins to direct the falling craft toward an ocean-based landing platform.
Unlike Falcon 9, however, China plans to ditch landing legs in favor of an innovative tether-catching system. Landing legs have proven a difficult engineering challenge for reusable rockets. The addition of legs creates drag and adds significant weight, reducing payload capacity. Landing legs need to be lightweight, reliably shock-absorbing, and reusable.
These extreme requirements have turned out to be something of an “impossible trinity.” Hence, SpaceX has abandoned landing legs entirely for Starship’s first stage, instead hoping to “catch” it upon landing using the launch tower itself. This removes significant mass and complexity from the rocket. China’s approach is similar in principle but potentially much simpler.
The new 921 promotional video shows a dual layer of parallel cables or tethers that tighten around the rocket as it approaches landing, catching the booster via hooks near the grid fins at the top of the stage. The cables, presumably with the “first layer” having some degree of elasticity, provide the necessary shock absorption needed to cushion the rocket without any moving parts.
Presumably, these cables can “tighten” in different directions/locations should the rocket not land dead-center on the landing platform. Catching the rocket from the top is “easier” as metals are stronger in tension than they are in compression. One can crush a soda can, for instance, but not tear it apart. Elastic tethers appear to be an elegant solution to what is otherwise a difficult engineering challenge.
An Exciting Future
China’s latest rockets, the LM-5, 6, and 7 series are not designed for reuse and cannot be retrofitted so. The 921 rocket will be a reusable and cheaper replacement for these launch vehicles. In addition, the triple-core version makes crewed lunar flights possible. China would need just two 921s to land a crew on the Moon: one launch for the crew capsule and another for a lander.
In sum, the 921 kills three birds with one stone. It is a quick way to catch up to SpaceX in reusability, it opens the door to crewed Lunar exploration by 2030, while also forming a stopgap for the more ambitious LM-9. More importantly, however, by abandoning the LM-9’s prior design and gearing up to quickly replace a relatively new series of rockets, China is demonstrating an admirable ability to avoid the “sunk cost” fallacy of continuing to invest in platforms simply because they are mature.
Ultimately, China’s approach to rocket landing and reuse will benefit the industry and humanity as a whole. More innovation and competition in this nascent sector will continue to drive down launch costs and, hopefully, open the door to a brighter future as a multi-planetary species.