.

YF-77 Engine BeijingAerospacePropulsionInstitute

.

Chinese engineers are proposing a Moon rocket more powerful than the Saturn V of the Apollo missions and matching the payload of NASA's planned Space Launch System (SLS) Block 2, the unfunded launcher that would put the U.S. back into super-heavy space lift.

Drawing up preliminary designs for the giant Long March 9 launcher, Chinese launch vehicle builder CALT has studied configurations remarkably similar to those that NASA considered in looking for the same capability: to lift 130 metric tons (287,000 lb.) to low Earth orbit (LEO). One of the two preferred Chinese proposals has a similar configuration to the design finally adopted for SLS Block 2, though the takeoff mass for both CALT concepts, 4,100-4,150 tons, is greater. On that measure, at least, China wants to build the largest space launcher in history.

Preliminary work is underway for the intended engines. At the Xian Space Propulsion Institute, engineers are certainly planning and probably doing risk-reduction work for a kerosene-fueled engine, apparently called YF-660, that would be comparable to the 690 tons thrust of the Saturn V's F-1. The Beijing Aerospace Propulsion Institute, meanwhile, is working on critical technologies for a 200-ton-thrust liquid-hydrogen engine that would be used for the first stage of one launcher design and for the second stage of both. That engine is apparently called the YF-220.

Comparison with current launchers and engines highlights the scale of China's ambitions: Whereas U.S. SLS engineers are aiming at a 10% increase on the throw weight of the Saturn V and would use mainly familiar propulsion technology, CALT's super-heavy launcher would have 10 times the throw weight of anything that China now has in service, and would be four times bigger than even the largest rocket it is developing—the Long March 5. The YF-660 engine would be five times as powerful as the biggest engine China has so far built, one that has not yet flown.

The Chinese industry is seeking permission to begin developing a Moon rocket. Studies encompass payloads as low as 70 tons to LEO, says an industry official, suggesting that China may follow the SLS concept by first building a smaller launcher adaptable to enlargement.

Possible Long March 9 configurations were shown two years ago. At the International Astronautical Congress held here Sept. 23-27, CALT published main specifications (see table). One of the two concepts, Scheme A, would have four YF-660s mounted in the core first stage and one in each of four side-mounted boosters. In Scheme B, most of the takeoff thrust would come from four solid-propellant boosters, each generating 1,000 tons of thrust, while four YF-220s would be mounted in the first stage. That adds up to 4,800 tons, but the specified total is 5,000 tons, suggesting that the solid-propellant booster engine, the YF-220 or both will generate a little more than the thrust attributed to each individually. The designation of the YF-220 may hint at its real thrust target.

“I don't find much to criticize in their approach, and a lot to like,” says an experienced U.S. space engineer.

The YF-220 exists as a concept or preliminary design, says Zhang Nan, president of the Beijing Aerospace Propulsion Institute, without using the name of the engine. His institute is channeling its experience in developing the YF-77 for the Long March 5 as it works on the new engine. So far, developers are tackling critical technologies and have not built parts for a flyable engine. A technology they will not attempt is staged combustion, a means of driving the pumps that, while maximizing engine efficiency, is hard to develop, especially for engines running on liquid oxygen and liquid hydrogen. In fact, it is too hard, says Zhang. The corresponding engine of the SLS, the Rocketdyne RS-25 from the Space Shuttle, does combine staged combustion with hydrogen fuel. The future Chinese engine's specific impulse (ISP)—thrust divided by fuel flow—may be as high as 430 sec., compared with 428 sec. for the YF-77, notes Zhang.

China's biggest kerosene-fuel engine, the YF-100, uses staged combustion, but applying the technology will be one of the many challenges that engineers will face in building bigger powerplants. Project managers at Xian appear to have minimized problems by adopting a plan they set out in 2011 and 2012 to first build an engine of more moderate size—300-400 tons thrust, presumably—and then doubling it for Long March 9 by feeding two of its combustion chambers with a single, more powerful propellant pump. A drawing of Long March 9 Scheme A has subtly changed since 2012 to show the extra nozzles of two-chamber engines.

Given the stated fuel loads and likely characteristics of the engines, the boosters of Scheme A are likely to burn for 160 sec. and the core for 220 sec., calculates a foreign rocket engineer. The second stage would run for 500 sec., presumably in several burns. If the Xian Institute can reproduce the efficiency of the YF-100 in the YF-660, then ISP at takeoff will be 305 sec. For Scheme B, the solid-propellant boosters may run for about 120 sec., the core first stage for 500 sec. and the second stage for 400 sec.

At 3.2%, the payload fractions of Schemes A and B are much lower than those of the Saturn V (3.9%) and SLS Block 2 (4.4%). This does not necessarily mean the Chinese design is inefficient, say engineers experienced in comparing launcher configurations; it may just reflect design choices that drive up takeoff weight but are nonetheless cost-effective. Solid-propellant boosters and their mounting structure probably account for much of Scheme B's excess of weight over Scheme A's.

The payload to LEO of the two designs suggests industry leaders here are eyeing lunar expeditions perhaps not much more ambitious than Apollo, although the mass they can deliver to the Moon's surface will also depend on how the mission is executed. Sending a crew aloft on a separate launch to join the rest of their spacecraft, carried by a Long March 9, could greatly expand the mission. The Saturn V, which lofted all Apollo modules in a single shot, had a payload to LEO of 118 tons.

At the International Astronautics Congress, the Chinese industry showed a concept for sending people to the Moon with three launches via smaller rockets. A cargo launcher, perhaps a little sibling of Long March 9, would fire a lunar-landing craft into orbit around the Moon. Then a crewed capsule would follow on an even smaller launcher, presumably a Long March 2F or Long March 7, China's current and future human-rated rockets, respectively. A propulsion unit sent on a second cargo launcher would join the capsule and propel it to lunar orbit, where it would meet the lander.

Smaller launchers are cheaper to develop, but bigger ones offer lower operating costs for their payload sizes. The economics of China's choice, then, must depend on whether it wants to sponsor heavy space missions for the long run, sending a super-heavy launcher up perhaps once a year, and not only to the Moon. If the aim is to perform a few manned lunar missions and then stop, it would surely be cheaper to execute each with multiple launches of moderately sized rockets. If more heavy-load tasks beckon, then a huge rocket is the answer, say Western engineers.

The Chinese space managers are on that wavelength. In the paper presented to the congress that detailed the Long March 9, CALT authors mentioned Moon shots, with a trans-lunar injection load of 50 tons, as only one purpose of the proposed launcher. Deep-space exploration (20 tons escaping Earth gravity), large-scale Earth-orbit missions (50 tons to geostationary transfer orbit) and new concept missions (50 tons escaping Earth gravity) were also touched upon, although the latter would require another rocket design.