Catastrophic failure assessment of sealed cabin for ultra large manned spacecraft in M/OD environment

First, authors analyze three typical catastrophic failures of manned spacecraft in an M/OD environment. For the astronaut casualty mode caused by low-pressure or hypoxic environment, hereinafter collectively referred to as astronaut hypoxic failure mode. In case of emergencies such as perforated gas leak that occurs in the cabin, the gas pressure control system in the sealed cabin should keep the total pressure not lower than P_TE, the oxygen partial pressure not lower than P_O2E, and duration not less than the critical escape time T_CE to support the astronauts in emergency on-orbit plugging or evacuation. When the perforation diameter D_h greater than the critical perforation diameter D_hE, the total pressure is lower than P_TE, or oxygen partial pressure is lower than P_O2E at T_CE, the astronaut hypoxia failure happens. In the analysis of the critical perforation diameter, variations in the internal pressure of the sealed cabin at a perforation diameter of D_h and the critical perforation diameter D_hE of the cabin at a given T_CE are obtained. Sealed cabin fracture failure mode refers to the situation where cracks induced by M/OD impact propagate or expand under the internal pressure of the sealed cabin, resulting in depressurization and then catastrophic failure of the cabin. When the stress intensity factor (SIF) at the tip of a crack on the cabin wall is equal to the fracture toughness of the wall material, the corresponding crack length is defined as the CCL of the sealed cabin. Under M/OD impact, if the crack length is greater than the CCL, SIF at the crack tip exceeds the fracture toughness of the material and, thus, the sealed cabin fractures. The relationship between SIF at the tip of an axial crack on a cylindrical cabin wall and crack length, which proposed by Folias, was used in this paper. Furthermore, spacecraft breakup is the most serious failure mode of manned spacecraft. The M/OD critical size criterion was used for cabin breakup failure mode assessment. When the M/OD particle impacted on the sealed cabin is larger than 3 cm in size, the spacecraft would fail to break up.

Then, authors establish the perforation and crack equations for stuffed Whipple shield of sealed cabin. The ballistic limit equations of the stuffed Whipple shield are derived in advance, which are important bases for studying perforation equations. To obtain the equations, hypervelocity impact tests on 3 types of stuffed Whipple shields were completed first, obtaining the ballistic limits of such shields. Then, on the basis of the genetic algorithms and multiple linear regression method, the coefficients of NASA’s Christiansen equation commonly used in the world were corrected, and finally the ballistic limit equations suitable for the stuffed Whipple shield of a specific ultra large manned spacecraft was obtained. With the above corrected ballistic limit equations of the stuffed Whipple shield and the perforation data of impact tests, the perforation equation for region 1 of the W-S hole equation was corrected, while the perforation equations for regions 2 and 3 and the crack length equation remain are consistent with those in the study of Williamsen and Schonberg in terms of form and coefficients. On this basis, the equations of perforation diameter and crack length on the sealed cabin were obtained, which are suitable for the stuffed Whipple shield of a specific ultra large manned spacecraft under different debris diameters and impact velocities. Moreover, depending on the structural parameters of 3 types of shield structures for a specific ultra large manned spacecraft and the modified perforation and crack equations, perforation diameter and crack length on the sealed cabin under an impact velocity of 3 km/s and an impact angle of 0° were predicted (Figs. 8 and 9).

At last, authors conduct catastrophic failure assessment of sealed cabin of ultra large manned spacecraft in M/OD environment. The assessment is based on the MODAOST framework (main modules are seen in Fig. 10), which is developed by the China Academy of Space Technology and has been successfully used for on-orbit PNP assessment of manned spacecraft of multiple models, such as the Tiangong-1 space module and the Tianhe core module. Among the modules in MODAOST, the impact characteristic database is used to describe failure modes of spacecraft and corresponding failure models. The impact characteristic database was expanded by adding the database modules of ballistic limit equations, perforation diameter calculation, and crack length calculation, as well as corresponding failure criterion modules of the sealed cabin structure that were supplemented. The catastrophic failure assessment of ultra large manned spacecraft is verified via the 3-module assembly of a specific ultra large manned spacecraft had an orbit of 400 km and an orbit inclination of 42°, flying in a triaxial stable attitude. Results show that among the typical failure modes, the gas-leakage-induced astronaut hypoxia is the primary factor, with the R factor reaching 0.159. Compared with the PNP assess method, the PNCF of the system achieved by the proposed method increases from 0.9970 to 0.9995, followed by the sealed cabin fracture, while spacecraft breakup is of the lowest probability. Under orbital debris impact, quadrants II and IV of the small column segment of the core module are the riskiest zones of perforation failure, while quadrant III of the small column segment is the riskiest zone under micrometeoroid impact. Authors pint out that the quantitatively catastrophic failure assessment of a specific ultra large manned spacecraft in an M/OD environment using MODAOST can provide reference for the design and assessment of long-term on-orbit missions of the spacecraft.