The Normandy is a prototype starship, developed by the human Systems Alliance with the assistance of the Citadel Council. It is optimized for scouting and reconnaissance missions in unstable regions, using state-of-the-art stealth technology.
For most ships, the heat generated through standard operations is easily detectable against the absolute-zero background of space. The Normandy, however, is able to temporarily sink this heat within the hull. Combined with refrigeration of the exterior hull, the ship can travel undetected for hours, or drift passively for days of covert observation. This is not without risk. The stored heat must eventually be radiated, or it will build to levels capable of cooking the crew alive.
Another component of the stealth system is the Normandy's revolutionary Tantalus drive, a mass effect core twice the standard size. The Tantalus drive generates mass concentrations that the Normandy 'falls into', allowing it to move without the use of heat-emitting thrusters.