## 2 Overview of Pressurized Capsule Structure
### The Development Course of Pressurized Capsule Structure  
The development of the pressurized capsule structure has gone through three stages: monocoque shell structure, semi-monocoque shell structure and the panel structure. The monocoque shell structure has no reinforcement parts, and the overall structure stiffness is low, so it is not suitable to bear large concentrated load and compression load. The semi-monocoque shell structure has longitudinal and transverse reinforcing members, which can withstand large axial and bending loads, and has large stiffness. For example, the Shenzhou spacecraft reentry module (as shown in Figure 5a), the Russian 'Soyuz' spacecraft orbit capsule and the Russian 'Salyut' space station pressurized capsule structure are all semi-monocoque pressurized capsule structures (s-MPCSs). Figure 4: Reinforced component of semi-monocoque shell and panel pressurized capsule structure. Table 1 summarizes the structure forms of common manned spacecraft pressurized capsules in the world. It can be seen from the table that the panel pressurized capsule structure gradually replaces the s-MPCS and becomes the mainstream form of the pressurized capsules. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Serial** & **Type** & **Spacecraft** & **Nation/Institution** & **Module Name** & \
\begin{tabular}{c} **First** \\ **Launch Date** \\ \end{tabular} &
\begin{tabular}{c} **Structure** \\ **Form** \\ \end{tabular} \\ \hline
1 & manned spacecraft & Vostok & Russia & pressurized capsule & April 196 & s-MPCS \\
2 & manned spacecraft & Mercury & USA & pressurized capsule & February 1962 & s-MPCS \\
3 & manned spacecraft & Voskhod & Russia & pressurized capsule & October 1964 & s-MPCS \\
4 & manned spacecraft & Gemini & USA & pressurized capsule & March 1965 & s-MPCS \\
5 & manned spacecraft & Soyuz & Russia & reentry capsule & April 1967 & s-MPCS \\  & & & & & \\
6 & manned spacecraft & Shenzhou & China & reentry capsule & November 1999 & s-MPCS \\
7 & manned spacecraft & Apollo & USA & command capsule & July 1969 & s-MPCS \\
8 & cargo spacecraft & Progress & Russia & cargo pressurized module & January 1978 & WPPCS \\
9 & cargo spacecraft & Automatic transfer & European Space & cargo pressurized module & March 2008 & WPPCS \\  & & of aircraft & Agency & & & \\
10 & cargo spacecraft & Tianzhou & China & cargo pressurized module & April 2017 & WPPCS \\
11 & space laboratory & Salyut & Russia & docking module & April 1971 & WPPCS \\
12 & space laboratory & Skylab & USA & orbital module & May 1973 & WPPCS \\
13 & space laboratory & Tangong-1 & China & experiment module & September 2011 & WPPCS \\
14 & space station & & Russia & core module & February 1986 & WPPCS \\
15 & space station & & Russia & Quantum-I/1 module & April 1987 & WPPCS \\
16 & space station & Mir & Russia & Crystal module & May 1990 & WPPCS \\
17 & space station & & Russia & Spectrum module & May 1995 & WPPCS \\
18 & space station & & Russia & Friroda module & April 1996 & WPPCS \\
19 & space station & & Russia & Zarya cargo module & November 1998 & WPPCS \\
20 & space station & & USA & Unity node module & December 1998 & WPPCS \\
21 & space station & & Russia & Zvezda service module & July 2000 & WPPCS \\
22 & space station & & USA & Destiny & February 2001 & WPPCS \\
23 & space station & International & USA & Quest airlock module & July 2001 & WPPCS \\
24 & space station & Space Station & Russia & & Department module & September 2001 & WPPCS \\
25 & space station & & USA & Harmony node module & October 2007 & WPPCS \\
26 & space station & & European & Columbus & February 2008 & WPPCS \\  & & & Space Agency & experiment module & & \\
27 & space station & & Japanese & & March 2008 & WPPCS \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of manned spacecraft pressurized capsule structures. Figure 5: Semi-monocoque shell and panel pressurized capsule structure. The panel pressurized capsule structure includes the development of the semi-monocoque shell structure.