In 2183, the Systems Alliance and the Turian Hierarchy co-developed the IES (internal emission sink) stealth system for small military frigates. It's unknown how the Initiative acquired this system for its survey ships, as IES stealth technology is classified. Despite valid security certificates, no record of negotiations exists in the Nexus legal archives.
An IES stealth system is designed to capture the heat and radiation emitted by all starships in refrigerated storage sinks, effectively removing the ship from sensors. Initiative starship systems are streamlined to emit less electromagnetic and particle radiation, and to lower heat production. This reduces the amount of emissions to be stored. Additionally, breakthroughs in cryogenic research allow the storage sinks to be more effectively refrigerated, allowing longer stealth time before the sinks must be vented for safety.
The Tempest can remain stationary in stealth for several hours, or travel at FTL in "silent running" for shorter periods.