Commercial Rockets

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. 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. 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.

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 uses no strap-ons of its own, and has dinky upper stages. The second stage burns kerosene conventionally, but the third is... I have little information, but one source says it burns kerosene hypergolically with peroxide. The 6 is designed for rapid preparation. Apparently there is also a 6A version in the works, which will use the full length two-engine version of the booster, and apparently have solid strap-ons — a first in their space program.

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. 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.

They are now working on proposed models 8 and 9. At first glance the 8 was just going to be a cheaper variant of the 7 using solid fuel for the side boosters, but then they decided that this was the one where they would try for reusability, with both the core and the side stages able to land themselves in some way, probably vertically like the Falcon. It looks, as far as I can tell from graphics they’ve shown, like it’ll use a lighter second stage than the 7 — perhaps an expander-cycle hydrogen burner, like a small version of the 5’s second stage — but that may be outdated information from the older expendable design. Another report says the new second stage will be based on the third stage of the 3A. 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.

The 9 is much more ambitious. If built, it will be enormous, with a capacity larger than the Saturn V and a mass of over 4100 tons. In their preliminary designs, it would apparently have 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, maybe that design is out now. Apparently the new plan is to increase the power of the core and ditch the side boosters. Details are not clear yet... this may or may not be connected to a plan to imitate SpaceX’s Starship. We shall see how this plan evolves.

And they might still cancel the Long March 9. The alternate plan is apparently to build a 5 Heavy with a triple core. But for now, the 9 is still going ahead. 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’re talking up plans to send people to Mars, and 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 top stage reenters the atmosphere. American 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.)

Long March 5: mass 879 t, diam 5 m (11.7 at base w/o fins), thrust 10600 kN, imp 4.2 km/s, type Gh+ZOk, payload 25 t (2.8%), cost unknown, record 6/0/1.
Stage name L-137 L-67 L-157 L-27 Yuanzheng-2
Role (pos) count booster (S) ×2?|4 booster (S) ×2?|4 core (1) upper (2), opt kick (3), opt
Diameter (m)   3.35   2.25   5.00   5.00
Liftoff mass (t) 150    73   171    33.6
Empty mass (t) 13   15    6.7
Fuel mass (t) ~37    ~18.1  ~24    ~4.5
Oxidizer mass (t) ~100     ~48.9  ~132     ~22.4 
Fuel type kerosene kerosene hydrogen hydrogen UDMH
Engine YF-100 ×2 YF-100 YF-77 ×2 YF-75D ×2 YF-50D
Power cycle staged (ZO) staged (ZO) gas gen closed expander ?
Chamber pres. (bar) 180    180    102    41  
Ox./fuel ratio   2.70   2.70   5.45   5.00
Thrust, vac max (kN) 2680     1340     1400     166nbsp;    6.5
Thrust, SL initial (kN) 2380     1190     1020    
Spec. imp, vac (km/s)   3.30   3.30   4.20   4.30   3.09
Total imp, vac (t·km/s) 445    215    658    117   
Long March 6: mass 103 t, diam 3.3 m, thrust 1200 kN, imp 2.9 km/s, type ZOk, payload 1+t?, cost unknown, record 7/0/0.
Stage name L-77 L-14 PBV? *
Role (pos) count core (1) upper (2) kick (3), opt
Diameter (m)   3.35   2.25   2.25
Liftoff mass (t) 84   15   1.0?
Empty mass (t)  1.6
Fuel mass (t) ~20.8  ~3.80
Oxidizer mass (t) ~56.2  ~9.6
Fuel type kerosene kerosene kerosene? *
Engine YF-100 YF-115 ?
Power cycle staged (ZO) staged (ZO) pressure-fed?
Chamber pres. (bar) 180    120   
Ox./fuel ratio   2.70   2.50
Thrust, vac max (kN) 1340     180    16  
Thrust, SL initial (kN) 1190    
Spec. imp, vac (km/s)   3.30   3.28   2.80
Total imp, vac (t·km/s) 248    44  
Long March 7 (four added boosters): mass 594 t, diam 3.3 m (7.8 at base w/o fins), thrust 7200 kN, imp 2.9 km/s, type ZOk, payload 13.5 t (2.3%), cost unknown, record 5/0/1.
Stage name L-67 or K2 L-137 or K3 L-72 ? (7A only) Yuanzheng-1A
Role (pos) count booster (S) ×0|2|4 core (1) upper (2) upper (3) kick (3|4), opt
Diameter (m)   2.25   3.35   3.35   3.00
Liftoff mass (t) 73   150    90   ~20   
Empty mass (t) 13   19  
Fuel mass (t) ~18.1  ~37    ~20.3   ~2.98
Oxidizer mass (t) ~48.9  ~100     ~50.7  ~15.2 
Fuel type kerosene kerosene kerosene hydrogen UDMH
Engine YF-100 YF-100 ×2 YF-115 ×4 YF-75(D) ×2 YF-50D
Power cycle staged (ZO) staged (ZO) staged (ZO)? gas gen ?
Chamber pres. (bar) 180    180    120    37.6 
Ox./fuel ratio   2.70   2.70   2.50 ~5.1 
Thrust, vac max (kN) 1340     2680     590    167.7   6.5
Thrust, SL initial (kN) 1200     2400    
Spec. imp, vac (km/s)   3.30   3.30   3.30   4.30   3.09
Total imp, vac (t·km/s) 215    445    235    ~78.2;