Before the successful Exploration Flight Test 1 (EFT-1) flight test in December 2014, the Orion EFT-1 Heat Shield suffered from two major certification challenges: First, the mechanical properties used in the design were not evident in the flight hardware, and, second, the flight article itself cracked in several locations during fabrication. These events motivated the Orion Program to pursue an engineering-level Loss of Mission Probabilistic Risk Assessment (PRA) as part of the Heat Shield certification rationale. The PRA provided likelihoods considering the probability of ablator cracks occurring during the mission and the likelihood of subsequent structure overtemperature. After a general discussion illustrating the relationship between typical stress design policy and reliability, the Orion-specific methods and input data for the PRA are presented along with a discussion of the test data used to anchor the results. The Orion program accepted an EFT-1 Loss of Vehicle risk of 1 in 160,000 due to in-mission Avcoat cracking based on the results of this analysis. Conservatisms in the result, along with future considerations for Exploration Missions, are also addressed.

在2014年12月成功进行探索飞行测试1（EFT-1）飞行测试之前，猎户座EFT-1防热罩遭受了两个主要的认证挑战：首先，设计中使用的机械性能在飞行硬件中不明显；以及其次，飞行物品本身在制造过程中会在多个位置开裂。这些事件促使Orion计划寻求进行工程级的任务损失概率风险评估（PRA），作为“热盾”认证依据的一部分。PRA考虑了在任务期间发生烧蚀裂纹的可能性以及后续结构过热的可能性，提供了可能性。经过一般性讨论，说明了典型的应力设计策略和可靠性之间的关系，提出了PRA特定于Orion的方法和输入数据，并讨论了用于锚定结果的测试数据。根据分析结果，Orion计划接受了因任务中的Avcoat破裂而导致的160,000的EFT-1车辆损失风险中的1。还讨论了结果中的保守性，以及对勘探任务的未来考虑。