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Zhang Tong

In the high‑stakes space race between the United States and China, the decisive advantage could come down to a metal cap that few outside the industry have ever heard of: the propellant tank dome.
An ellipsoidal bulkhead several metres wide but only millimetres thick, the dome must withstand extreme internal pressures, vibration and shock. The rounded, capsule-like end cap is also very difficult to mass-produce.
Whichever country can make these components faster, cheaper and more reliably will have an advantage in building the large fleets of reusable rockets needed for the future space economy.


Now, China is signalling that it may have found not one but two ways to break the bottleneck.
On Friday, the country’s Long March 10B (CZ-10B) delivered satellites into orbit and then made a vertical descent into a giant buffer net aboard an offshore recovery platform. The moment marked China’s first recovery of a reusable rocket.
The flight showcased a dome made with a welding method benchmarked against SpaceX’s Falcon series but potentially faster off the production line.
At the same time, Chinese researchers have unveiled a revolutionary “cold forming” technique that can shape a complete, seamless dome in a few hours rather than a week – an advance that could tilt the balance of the US-China space race in the years ahead.
For the CZ‑10B, the tank dome was made by Shanghai Top Numerical Control Technology, using domestically developed machine tools and manufactured to standards benchmarked against SpaceX’s Falcon series, according to a social media post by the company on Friday.
Two core processes are used.
The first is Shanghai Top Numerical’s dual five‑axis mirror milling, which machines the dome integrally with a backing support on the reverse side to prevent the thin material from deforming under cutting loads, ensuring precision and efficiency.
Only three suppliers worldwide can offer such mirror‑milling technology: Dufieux of France, M. Torres of Spain, and Shanghai Top Numerical, with the Chinese equipment boasting advantages in machining accuracy, cycle time and cost.
The second process addresses the joint between the dome and the tank barrel, a 5-metre (16.4-foot) friction-stir welding system.
By rotating a stirring tool at high speed, the friction generates heat that softens and kneads the metal together, forming a defect-free weld.
This method increases the fatigue strength of the joint several times over conventional fusion welding, giving the durability needed for a rocket to fly repeatedly without structural failure.

Shanghai Top Numerical Control said the combination of these two technologies “is precisely the core manufacturing pathway that enables the high-reliability recovery of SpaceX’s Falcon series”.
Compared with traditional segmented fabrication processes, this approach “trims nearly 400kg (882lbs) from the dome of a single rocket, and relevant technical indicators already surpass the benchmark set by leading international peers”, the company added.
While this is a proven industrial route that China is rapidly catching up to, another parallel path pursued by mainland researchers aims to go a step further.
According to a report on Sunday by the official China Science Daily, a team from Dalian University of Technology specialising in high-performance precision forming has been working since 2018 on a cryogenic integral-forming technology for aluminium alloys.
The breakthrough came from a serendipitous discovery: contrary to the conventional wisdom that metals become brittle and lose strength at low temperatures, the team found that, under specific ultra-low temperatures, aluminium alloys actually exhibit simultaneous increases in both elongation and work-hardening exponent.
Using this physical effect, the team developed a proprietary forming process that takes a 4mm-thick aluminium alloy sheet, places it in a cryogenic chamber at minus 196 degrees Celsius (minus 321 Fahrenheit) and shapes it in a single stroke into a seamless, smooth-surfaced integral dome that requires no further machining and is ready for direct use.
Compared with the traditional approach of forming separate segments and then welding them together, this ultra-low-temperature integral forming boosts material utilisation to over 85 per cent and cuts production time from more than a week to just a few hours – a reduction of more than 90 per cent.
Working closely with the China Academy of Launch Vehicle Technology (CALT), the team has already seen its novel domes fly successfully on the Long March 12 and the Long March 7A Y14 missions.
Furthermore, in partnership with Tianjin Harbin Gongda Yongxing Technology, the university has built a dedicated 4-metre-class production line for integral tank domes in the Jizhou Economic Development Zone in Tianjin.
In May, the first batch of mass-produced domes rolled off the line, with an annual capacity exceeding 1,000 units – enough to support the assembly of more than 100 rockets per year.
“In the future, the team will aim for larger rocket structures – over 5 metres in diameter and with strength above 1,000 [megapascals]. This will help China make rockets more cheaply, more efficiently and on a bigger scale,” China Science Daily reported.


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Propellant tank dome that is only millimetres thick must withstand extreme internal pressures and is very difficult to mass-produce


Propellant tank dome that is only millimetres thick must withstand extreme internal pressures and is very difficult to mass-produce.


Why the US-China space race could come down to a thin metal cap

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Propellant tank dome that is only millimetres thick must withstand extreme internal pressures and is very difficult to mass-produce

Propellant tank dome that is only millimetres thick must withstand extreme internal pressures and is very difficult to mass-produce