Rockets of Today

LONG MARCH (Chángzhēng, 长征) — new models — China, 2015

The Chinese finally got tired of hypergolic fuel, what with its toxicity and pollution and mediocre performance, so they started working on some more modern rockets with cryogenic fuels. They’re also tired of dropping spent rockets onto rural villages, so they’re finally building some launch facilities on an island. And to start off this new era, they decided to build something big. They called it the Long March 5 — informally, the “fat five” (pàng-wū). And as before, they are making a modular system out of it.

Like the Long March 2 and 3, the 5 has four liquid fueled strap-on boosters. Each side booster has two kerosene burning staged combustion YF-100 engines, and is the size of a core stage from a classic Long March 2, 3, or 4. And later, there are supposed to be two versions of the side booster, with the other being a skinny version with only one engine, but that has yet to fly. They even talk about an in-between version of the rocket, using two fat boosters and two skinny ones. The new king-sized core stage also has two engines, and as in the Ariane 5, they burn hydrogen. This new engine is called the YF-77. The upper stage also has two hydrogen engines, in a much smaller size, and there’s an optional hypergolic third stage. This rocket has plenty of muscle, and thanks to the hydrogen, plenty of delta-V for high orbits. It can throw six tons at Mars. But its second flight was a failure due to a bad YF-77 turbopump, so it has been a struggle to get the thing into regular use. After three launches they added a 5B version, which has no upper stage. It’s intended for heavy loads in low orbit, which go directly atop the hydrogen core. They use this for space station modules. And they’re working on a triple core version called the 5G or 5 Dengyue, which they intend to use to send people to the moon. They’d use two of them: one for the crew and one for the lander.

They also wanted a small modern rocket, so they made the Long March 6 by taking one of the new fat side boosters, shortening it, removing one engine, and using that as a first stage. This was the first rocket in the new family to fly. It used no strap-ons of its own in its original version, and had dinky upper stages. The second stage also burns kerosene, and the third is hypergolic. The 6 is designed for rapid preparation. There is also now a 6A version which uses the full length two-engine version of the booster, and is their first rocket to use solid strap-ons. It also has a fatter second stage than the original 6. Add up all those upgrades and the 6A can do four tons to sun-synchronous orbit (the only figure they give), where the original only did one ton.

And finally, they wanted a midsize rocket to carry forward the classic design of the old school Long March models, reusing many of the old parts — specifically, those of the 2F — with the new motors. This became the Long March 7, though at first it was provisionally just called the 2F/H. This also uses YF-100 engines (or a very similar related model), and essentially they just put four of the new skinny boosters around one of the fat ones. This means the 6A would pretty much be just a 7 without the strap-ons... at least superficially. Behind the scenes, though the 6 and the 7 use compatible dimensions and engines, the two were actually developed by different teams, and have many differences — the 7 being a direct offshoot of the Long March 5 project and the 6 being done by the Shanghai Academy of Spaceflight and Technology. In 2020 they added a 7A which has a hydrogen-burning upper stage, updated from the one used on the Long March 3. You could say that the original 7 replaces the Long March 2 and the 7A replaces the Long March 3. I guess the 6 could be considered as the new Long March 4, though it’s a step down in capacity. So the new system covers a wider range than the old, at both ends. Between the 6 and 7, they ended up cancelling the lighter versions of the 5 — they had originally planned to not only include a version with no side boosters, but also to make the core stage in two different diameters.

With the Long March 5/6/7 project they also debuted a new kick stage, the Yuanzheng-1, which can deposit satellites in high or multiple orbits. It uses hypergolics, and can fly on the old rockets as well as the new ones.

Then they started on a Long March 8. The basic idea of the 8 is to be the 7 but cheaper. It uses the same core stage as the 7, and for now the same side boosters, though only two. The only real difference from the 7 is in the second stage, which is the hydrogen burning third stage from the Long March 3 and 7A, bumped down to second position. They could have just called it the 7B, but they intend that over time it will diverge more significantly from the 7. The original plan was to replace the liquid side boosters with solid ones, but now they intend to make it reusable, and land the core stage with the boosters still attached. If that works, the 7 may become obsolete. As yet the 8 has only made expendable flights, and this will apparently be true for some time to come. They apparently plan to put grid fins on the core stage, like a Falcon; such fins have been added to a Long March 4 booster to try them out. They want to achieve reuse by 2025.

They also want to increase the smarts of their automation, using AI techniques. They say at least a third of historical rocket failures could have been prevented if the guidance control had been more intelligent and adaptable. These improvements will be tested in the old Long March series, which will be upgraded for as long as they stay in service.

For the longer term, they are also working on a Long March 9, which is much more ambitious. If built, it will be enormous, with a capacity larger than the Saturn V and a mass of over 4000 tons. In their preliminary designs, they were apparently looking at having four kerosene engines on each of the four side boosters, and four really big dual-nozzle kerosene engines on the core. The core would be 9.5 or 10 meters across — as thick as a Saturn V first stage, and a lot taller — and each booster five meters wide, like the core stage of the 5. The Russian Yenisei would look puny next to it, though the 9’s gain in capacity over the Yenisei would be only about 40 percent. Even the upper stage would be not much smaller than Apollo’s second stage. They’re building a new staged-combustion hydrogen engine for that derived from the YF-77 gas generator used in the 5’s core stage, but with triple the thrust. They will try for some reuse in the 9, but not at first.

No wait, that design has now been dropped, along with the big YF-133 kerosene engine it would have used, which was apparently already well along in development. They're starting over with a new plan: imitate SpaceX. The new tentative design is a methane-burning reusable first stage ten meters in diameter, with grid fins but no visible legs. The expendable second stage would be enormous, and a third stage atop that would give it a 150 ton capacity. We shall see how this evolves.

And they might still cancel the Long March 9. The alternate plan is apparently to build a 5 Heavy with a triple core, and also make a reusable version of that booster, which will become the carrier for their new crew capsule. But for now, the 9 is still going ahead, though perhaps less aggressively. They want to use it to send a sample return mission to Mars, and eventually people. But they don’t expect the 9 to fly until 2030. With that big boy, they also hope to put huge solar arrays into geosynchronous orbit.

Speaking of ambition, their last two missions for the 5 were a Mars lander, and a lunar lander that successfully brought moon rocks back to Earth. Then they commenced building a space station with the 5B. They’re planning a second moon-rock flight, and two orbital telescopes. And note that the maiden 5B flight was a test of a new crew capsule. They’re counting on this beast for the kinds of high-prestige missions which will put China solidly in the front rank of space powers. And China is already so active and ambitious in space that I think Russia is now clearly the number three spacefaring nation.

One controversial aspect of these missions is that they don’t control where the stages reenter the atmosphere. Most rockets save a drop of fuel for the upper stage to put itself back into the atmosphere when and where it’s safest to come down. But the Chinese don’t, and with the 5B especially, this means that a really big core stage with heavy engines might come down in an inhabited area.

(There’s also a Long March 11, which is a quick and dirty solid fuel job with four stages, which they keep around if they need to do an emergency launch in a hurry and nothing else is available. This was covered in the earlier article on China’s missile-derived solid fuel launchers.)