Newswise — Micrometeoroid and Orbital Debris (M/OD) pose grave risks to manned spacecraft and astronauts in orbit due to hypervelocity impacts. Currently, M/OD larger than 10 cm, which can be anticipated and tracked in advance, can typically be evaded through orbital maneuvers. However, smaller M/OD particles present a significant threat as they are challenging to monitor. Consequently, they become the primary focus of impact risk evaluation and protection design for manned spacecraft. The assessment of sealed cabin integrity, determined by the probability of no penetration (PNP) under M/OD impact, serves as a method to evaluate the system's failure probability in manned space missions. Various methods have been developed to gauge the M/OD impact hazard, including PNP, the probability of no catastrophic failure (PNCF), and Manned Spacecraft Crew Survivability (MSCSurv). These methods ascend in accuracy when assessing the safety and survivability of manned spacecraft and astronauts. Presently, China employs the PNP of sealed cabins to assess the likelihood of catastrophic failure in the design of manned spacecraft, leading to imprecise risk evaluations in M/OD environments. Consequently, further research must be conducted to enhance the assessment of catastrophic failure in sealed cabins of Chinese manned spacecraft. In a recent research paper published in Space: Science & Technology, several scholars examined critical perforation diameters and critical crack lengths of sealed cabins, focusing on typical catastrophic failure modes. They developed a failure assessment module to enhance the M/OD Assessment and Optimization System Tools, originally created by the China Academy of Space Technology. Furthermore, they established ballistic limit equations, perforation equations, and crack equations specifically suitable for stuffed Whipple shields. These findings offer valuable insights for the design and assessment of long-term on-orbit missions for ultra large manned spacecraft operating in M/OD environments.
Initially, the authors examine three major catastrophic failures in the presence of Micrometeoroid and Orbital Debris (M/OD) for manned spacecraft. The first failure mode, collectively known as astronaut hypoxic failure mode, involves astronaut casualties due to low-pressure or hypoxic environments. In emergencies like cabin gas leaks, the sealed cabin's gas pressure control system must maintain a total pressure not below PTE, an oxygen partial pressure not below PO2E, and a duration of at least the critical escape time TCE. This ensures support for astronauts during emergency plugging or evacuation in orbit. Astronaut hypoxia failure occurs when the perforation diameter Dh exceeds the critical perforation diameter DhE, or when the total pressure or oxygen partial pressure falls below the specified levels at TCE.
The analysis of the critical perforation diameter involves examining variations in the internal pressure of the sealed cabin at a given perforation diameter Dh and the critical perforation diameter DhE for a specific TCE. Sealed cabin fracture failure occurs when cracks induced by M/OD impacts propagate or expand under the internal pressure, resulting in depressurization and catastrophic failure. The crack length corresponding to the stress intensity factor (SIF) equaling the fracture toughness of the cabin wall material is defined as the Critical Crack Length (CCL) of the sealed cabin. Under M/OD impact, if the crack length exceeds the CCL, the SIF at the crack tip surpasses the fracture toughness, leading to cabin fracture. This paper utilizes Folias' proposed relationship between SIF at the tip of an axial crack on a cylindrical cabin wall and crack length.
Furthermore, spacecraft breakup is the most severe failure mode for manned spacecraft. The assessment of cabin breakup failure mode employs the M/OD critical size criterion. If an M/OD particle impacting the sealed cabin is larger than 3 cm in size, the spacecraft fails to withstand the impact and undergoes breakup.
Next, the authors focus on establishing perforation and crack equations specifically for the stuffed Whipple shield of the sealed cabin. Initially, ballistic limit equations for the stuffed Whipple shield are derived, serving as essential foundations for studying perforation equations. To obtain these equations, hypervelocity impact tests were conducted on three types of stuffed Whipple shields. These tests provided the necessary data to determine the ballistic limits for these shields. Subsequently, using genetic algorithms and the multiple linear regression method, the coefficients of NASA's widely used Christiansen equation were corrected. This led to the development of ballistic limit equations specifically suitable for the stuffed Whipple shield of a particular ultra large manned spacecraft.
Using the corrected ballistic limit equations and the perforation data obtained from impact tests, the authors then corrected the perforation equation for region 1 of the W-S hole equation. However, the perforation equations for regions 2 and 3 and the crack length equation remained consistent with the study conducted by Williamsen and Schonberg in terms of their form and coefficients. Building upon this, the authors obtained the equations for perforation diameter and crack length on the sealed cabin, which are suitable for the stuffed Whipple shield of the specific ultra large manned spacecraft under different debris diameters and impact velocities. Furthermore, leveraging the structural parameters of the three types of shield structures for the specified spacecraft and the modified perforation and crack equations, predictions were made for the perforation diameter and crack length on the sealed cabin under an impact velocity of 3 km/s and an impact angle of 0°.
Finally, the authors proceed with the catastrophic failure assessment of the sealed cabin of an ultra large manned spacecraft in an M/OD environment. This assessment is conducted using the MODAOST framework, which was developed by the China Academy of Space Technology and has been successfully applied to assess the probability of no penetration (PNP) in on-orbit manned spacecraft of various models, including the Tiangong-1 space module and the Tianhe core module. The main modules of MODAOST are depicted in Figure 10.
Within the MODAOST framework, the impact characteristic database plays a crucial role in describing spacecraft failure modes and their corresponding models. To enhance the database, modules for ballistic limit equations, perforation diameter calculation, crack length calculation, and the corresponding failure criteria for the sealed cabin structure were added. The assessment of catastrophic failure in the ultra large manned spacecraft was validated using a specific spacecraft model that orbited at 400 km with an inclination of 42°, maintaining a triaxial stable attitude.
The results reveal that among the typical failure modes, astronaut hypoxia caused by gas leakage is the primary factor, with an R factor of 0.159. Compared to the PNP assessment method, the proposed method achieves an increased probability of no catastrophic failure (PNCF) for the system, rising from 0.9970 to 0.9995. Sealed cabin fracture follows astronaut hypoxia as the next significant failure mode, while spacecraft breakup exhibits the lowest probability. Under the impact of orbital debris, quadrants II and IV of the small column segment of the core module are identified as the riskiest zones for perforation failure, while quadrant III of the small column segment poses the highest risk under micrometeoroid impact.
The authors emphasize that the quantitative assessment of catastrophic failure in a specific ultra large manned spacecraft within an M/OD environment using the MODAOST framework can provide valuable guidance for the design and assessment of long-term on-orbit missions for such spacecraft.
Reference
Article Title: Catastrophic Failure Assessment of Sealed Cabin for Ultra large Manned Spacecraft in M/OD Environment
Journal: Space: Science & Technology
Authors: Jiangkai Wu, Zengyao Han, Runqiang Chi*, Shigui Zheng, and Yong Zhang
Affiliation: Harbin Institute of Technology, Harbin, 150001 Heilongjiang Province, China
RSS