Summary of Key Points
Chinese commercial rockets are transitioning from early, small-to-medium-sized solid rockets to larger liquid rockets designed for satellite constellations, with increasing rocket diameters (ranging from 1.4 meters to 4.5 meters). However, a larger diameter does not necessarily mean more advanced technology; it is the result of combined factors such as mission requirements, manufacturing capabilities, and transportation conditions. Larger-diameter rockets require corresponding ground facilities (factories, transportation systems, launch pads) and sufficient launch orders to realize their advantages; otherwise, they can lead to increased costs. The strength of a rocket should not be judged solely by its diameter but also by the differences in its core stages and fairings, payload capacity, reusability system, and launch frequency.
Detailed Analysis
1. Don’t Be Misled by Diameter Numbers: Core Stages and Fairings Are Different
The “rocket diameter of X meters” often mentioned in promotions may refer to two different parts:
- Core Stage: The main body of the rocket that contains the propellant and engines, responsible for carrying the payload. It is the critical component that determines the rocket’s payload capacity.
- Fairing: The covering at the top of the rocket that protects the satellites. A larger fairing allows for the placement of larger or more satellites, but it does not imply a thicker core stage or greater payload capacity.
For example, the Long March 2 rocket has a core stage diameter of only 3.35 meters, while its fairing can reach 5.2 meters; in promotions, it might be described as a “5-meter-class” rocket, but the actual core stage is not that large. A larger fairing is useful for improving satellite stacking efficiency, but if the core stage’s thrust and fuel capacity are insufficient, a larger fairing won’t increase the payload capacity—just like carrying a heavy backpack when you lack strength.
2. Larger Rockets Are Not Just For Show; They Are a Result of Mission Needs
Early commercial rockets (such as the 1.4-meter-long Ceres-1) used smaller sizes because they were designed to deliver small satellites or for technical demonstrations. Nowadays, with the need to deploy low-earth orbit constellations (hundreds to thousands of satellites), multiple satellites must be launched at once, and rocket reusability is also a consideration:
- Reusability requires fuel for the return journey and additional components like landing legs and grid fins, which increase the weight. Therefore, larger rockets are needed to accommodate this extra payload.
- A thicker core stage allows for more fuel and additional engines without increasing the overall length of the rocket, providing better structural flexibility.
However, rockets with the same diameter can have significantly different payload capacities. For instance, both the Long March 2 and the ZhiShen-1 have a 3.35-meter core stage, but the Long March 2 has a lower low-earth orbit payload capacity (12 tons vs. 7 tons). The Falcon 9’s core stage is only 3.7 meters in diameter (smaller than some domestic rockets under development), yet it can launch and reuse frequently due to its mature manufacturing, launch, and reusability systems—not because of its diameter.
3. The Hidden Barriers of Larger Diameters: Transportation and Launch Infrastructure
A 3.35-meter diameter is a “traditional size” for Chinese rockets due to railway transportation limitations (roads and bridges cannot accommodate larger sizes). Beyond this, additional challenges arise:
- Transportation: The Zhuque-3 rocket with a 4.5-meter diameter must be transported over 4000 kilometers from Jiaxing to Jiuquan by road, requiring careful planning for bridge and tunnel heights and turning radii. The Long March 5, with a 5-meter diameter, can only be transported by sea from Tianjin to Wenchang in Hainan.
- Launch Facilities: When the rocket arrives at the launch site, the lifting equipment, fueling systems, and launch pads must be adapted to accommodate the larger diameter (the original 3.35-meter facilities are not suitable). Foreign rockets (e.g., Starship with a 9-meter diameter) combine manufacturing and launch sites to reduce transportation complexities.
These infrastructure improvements require significant investment by the companies, similar to building a road for an oversized truck or constructing a garage to accommodate it.
4. Can Larger Diameters Be Profitable? It Depends on Launch Frequency
The benefits of larger rockets become evident only with frequent launches:
- If a rocket can be launched more than 10 times per year, the costs of construction, transportation, and launch facilities can be spread over multiple missions, turning higher payload capacity into revenue.
- If launches are infrequent (e.g., once every few years), the resulting downtime and maintenance expenses can be detrimental to the company’s finances—like renting a large warehouse with no cargo to store.
Therefore, a larger diameter is not always better. Small satellites do not require a 4-meter rocket for quick launches, while reusable rockets for constellations may benefit from a larger diameter, but only if there are enough orders to ensure continuous operations. Diameter is just one factor in engineering decisions; it does not indicate technological superiority. A 3.35-meter rocket is not necessarily less advanced, and a 4.5-meter rocket is not automatically more advanced.
In summary, increasing the rocket diameter is just the first step; the real challenge is to ensure there are sufficient launches to justify the investment and to reduce costs. Otherwise, even a larger rocket remains just an empty shell without practical benefits.