China is nearing what many space engineers think is the ideal for a family of space launchers: a set of rockets built with just a few standard engines and airframe modules, maximizing production runs. The family—the Long March 5, 6 and 7—will cover the 0.5-25-ton payload territory to low Earth orbit and up to 14 tons to geosynchronous orbit, meeting the great bulk of space launch demands.

So it may come as a surprise that the launcher and engine firms under national space industry group CASC are not satisfied. They are looking at introducing solid rockets into the mix, as boosters or small launchers, including some dropped from aircraft. The Long March 7, at least, will get non-standard second stages as its manufacturer, CASC subsidiary CALT, looks for ways to vary its payload (see following article). Chinese engineers are also working on engines fueled by methane or liquefied petroleum gas.

Although the major engine for the new launcher family, the YF-100, is now revealed to offer excellent performance with an advanced operating cycle, the industry's main propulsion center, the Academy of Aerospace Propulsion Technology (AAPT), sees reasons to replace it with a much bigger unit. Under that scheme, the big new engine would then be doubled to form the basis of a second powerplant for China's proposed Moon rocket.

Yet maybe all this should not come as a surprise. China's space program is clearly well funded. And the country's devotion to engine development was flagged in 2010 when CASC President Ma Xingrui told a delegation of U.S. space engineers and scientists: “I remind government leaders that engines are the heart of space launch technology, and that is where money must be invested.”

The engine developers have quite a few ideas of how they can spend the money that Ma is obtaining for them, beginning with the expectation that China needs two launchers bigger than the Long March 5—one lifting more than 35 tons to low Earth orbit for manned missions, and the “super-heavy” Moon rocket, research on which has been approved.

With no engine producing more thrust than the 120-metric-ton (260,000-lb.) YF-100, China is still far behind other countries in space propulsion, AAPT engineers Li Ping, Li Bin and Zou Yu told the Asian Joint Conference on Propulsion and Power here on March 2-3. “The thrust requirement of future Chinese heavy or super-heavy launch vehicles is on the order of 4,000-7,000 kn [900,000-1,570,000 lb., about 400-700 tons]” per engine, the officials write in the paper, part of which was also published last year, attracting little attention.

Such an engine would represent a technical and economic challenge. The proposed solution is to first make the largest engine for which China has a viable commercial use, using familiar liquid oxygen (LOX) and kerosene propellants.

“Based on available technologies and test facilities in China, it is possible to develop a 2,000-3,500-kn [450,000-790,000] class LOX-kerosene engine with single chamber in [a] short time,” say the AAPT engineers. This engine “can be applied to optimize the configuration of [the Long March 5] launch vehicle to reduce engine number and to increase reliability. The second step is to develop the 4,000-7,000-kn-class heavy thrust engine with double chambers with a heavy-power turbo pump.”

CALT has said that a Moon rocket would need 3,000 tons (6.6 million lb.) of thrust at liftoff. In an earlier paper, Li Ping and Li Bin showed two possible launcher configurations. Both had two 9-meter-dia. (29.5-ft.) core stages (compared with a maximum of 10.1 meters on the Saturn V first stage) and four 3.35-meter-dia. kerosene-fueled boosters. In one configuration, the first core stage was fueled by hydrogen, which gives more impulse for its mass, and the other by kerosene, which would be easier to develop and is now backed by the researchers.

The upper stage would use hydrogen. In the earlier paper, the engineers say it is “necessary” to develop a new hydrogen engine of 1,500-2,000 kn, compared with the 700 kn of China's current largest, the YF-77 of the Long March 5.

In its biggest configuration, the Long March 5 will have four boosters each mounting two YF-100 kerosene engines, plus two hydrogen-fueled engines in the core. Using 10 engines at liftoff heightens the risk of failure, and so the Long March 5's design has been highly controversial in the Chinese industry.

Separately, China has been working on a staged-combustion hydrogen engine for the highest possible specific impulse. The Long March 5's core engines use the simpler gas-generator cycle.

The paper presented to the conference can be taken as an approved guide to AAPT's thinking, since its contents would not be discussed without careful consideration by the authorities. But development of the proposed engines and their launchers has not been approved; AAPT and CALT could yet decide on another path.

New solid-rocket launchers are definitely on the way. The Long March 6, using a YF-100 first stage, has been described as small, responsive launcher, meaning that it can be used promptly. But CALT Principal Engineer Shen Lin told the conference there would be a “new generation of solid launch vehicles, air-launch vehicles and LOX-methane liquid launch vehicles [following a] concept of quick response, small size, low cost and high reliability.”

These launchers will loft small satellites to help deal with natural disasters, Shen says. Western analysts also see military uses—potentially hurling anti-satellite warheads or rapidly launching a reconnaissance spacecraft to acquire urgent targeting data.

Solid-propellant rockets can be launched much faster than even small liquid-propellant rockets such as the Long March 6, notes Eric Hagt, a U.S. analyst who closely follows Chinese space activities. And in modern battle concepts, “immediacy is pretty important.”

Shen gave no figures indicating the size of these solid-propellant rockets, but one industry official says they may also be introduced as boosters for the new Long March family, with the aim of cutting costs—even though that seems counter to the economical scheme of kerosene-fueled modules. China is developing segmented solid rocket boosters, say Li Ping and Li Bin. If the new boosters are related to the new solid-propellant launchers, then the latter are probably not closely related to Kaituozhe 1 (Explorer 1) launcher, a ballistic-missile derivative revealed in 2001.

The Chinese will have to build the solid-propellant launchers at a fairly high rate, perhaps exploiting modularity and segmentation, says a senior U.S. space technology executive. Otherwise they could turn out to be more costly than liquid-propellant engines. The air-launched rockets would be part of the solid-propellant family, says a Chinese official.

The solid-propellant development is not the only Chinese propulsion effort that raises questions of duplication. Foreign executives wonder why China is bothering to pursue a methane launch engine when it already has good powerplants of the right size using kerosene and hydrogen.

Engineers have tested methane fuel by adapting hydrogen engines, using turbopumps instead of tank pressure to feed the combustion chamber, says a Chinese official. A thrust of 60 tons has been officially disclosed, along with possible uses for methane in spacecraft, as distinct from launchers. But Shen's remarks associated the technology with rapid-response launchers—suggesting that Chinese engineers are working on three kinds of engines for the same task: kerosene, solid and methane. Moreover, China plans to develop a kerosene engine for in-space use, seeming to duplicate the methane work in that area, too. Chinese engineers have also investigated using liquefied petroleum gas as a fuel.

While some CALT engineers are drawing up their plans for the two launchers that would surpass the Long March 5, others are looking further into the future at reusable or semi-reusable spacecraft. At this early stage, the most promising prospect seems to be a winged orbiter that would act as a second stage on an expendable first stage, says one person familiar with the studies.

CASC's full name is the China Aerospace Science & Technology Corp. and CALT's is the China Academy of Launch Technology. The Xian conference brought together researchers from China, Japan and South Korea.