Standards-based wireless sensor network (WSN) protocols are promising candidates for spacecraft avionic systems, offering unprecedented instrumentation flexibility and expandability. However, when migrating from wired to wireless data gathering systems, ensuring reliable data transport is a key consideration. In this paper, we conduct a rigorous laboratory analysis of the relative performance of the ZigBee Pro and ISA100.11a protocols in a representative crewed aerospace environment. Since both operate in the 2.4 GHz radio frequency (RF) band shared by systems such as Wi-Fi, they are subject at times to potentially debilitating RF interference. We compare message delivery rates achievable by both under varying levels of 802.11g Wi-Fi traffic. We conclude that while the simpler, more inexpensive ZigBee Pro protocol performs well under moderate levels of interference, the more complex and costly ISA100.11a protocol is needed to ensure reliable data delivery under heavier interference. This paper represents the first published, rigorous analysis of WSN protocols in an aerospace analog environment of which we are aware and the first published head-to-head comparison of ZigBee Pro and ISA100.11a.