At the height of the cold war, the B-2 was designed to fly stealthily across the north pole and into Russian territory to destroy Russion nuclear missile silos. It was designed to do this even AFTER World-War-III had started, doing it's job with no external help from AWACs, GPS satellites, fighter cover, or any other assistance typically used in modern airial wafare. This mission required extreme stealth so as not to be detected (and destroyed) by the Russians, extreme independance in navigation and target acquisition, and extreme reliability. Invisibility had to be maintained against radar and thermal detection devices.
For this reason, the B-2 required a tiny radar cross-section, which is obtained by virtue of it's shape and materials... the shape has no vertical surfaces to reflect to radar transmissions looking at it from the side. There are no vertical stabilizers to refelct radar transmissions. There are no exposed engine components. The engines (whose turbine blades are typically a give-away on radar) are buried deep in the wing, totally invisible from the outside no matter what angle you lok at the airplane from. The curved ducts to and from the engine are coated with RAM (Radar Absorbing Material) to keep any stray radar beams from bouncing into or out of them.
The B-2 is made primarily out of composites (largey carbon-fiber) because metal construction would result in small SEAMS where the metal parts are joined... a dead give-away on radar. Composites, however, can be manufactured in large, curved parts that can then be "co-cured" (or baked) together to form an aircraft with no radar-detectable seams where the parts meet. This process is implemented on the B-2, resulting in a few large skin components that are baked together to form a perfectly smooth and seamless external shell... it was then up the engineers to fit the internal structure and systems inside of that shell... this is opposite from the way any other airplane has been designed and built... normally the structure is designed to suit the aerodynamics and load-carrying requirements, a frame is built, and the skin is then laid up on top of the internal structure... not so with the B-2 which had to meet the external shape required for stealth... this process had to be reversed, with all parts made to fit inside the pre-defined external shape of the aircraft. The carbon fibre that comprises much of the B-2 structure is good for shaping and low radar observability, but would be destroyed by lightning and and heat from the engine exhaust. Also the flexing of the wing in turbulence would change the shape of the wing enough in flight that radar observability would increase, reducing the sealth efficiency... these things resulted in Northrop testing over 900 materials, and stiffening the structure signifigantly, during the development program.
Thermal emissions are also problematic, since Soviet satellites could detect the heat trail of the aircraft from orbit. The B-2 therefore mixes cool air from the atmosphere with the hot air from the engine exhaust to result in a cooler heat signature from the airplane.
The aircraft might also be spotted VISUALLY by observation of it's contrails. Contrails have been broken up in aircraft before by injecting toxic and corrovice chemicals into the exhaust stream that break the water droplets into a smaller size than the wavelength of visible light. It is also SUSPECTED that there is a light sensor on the B-2 which will tell the pilot to climb or descend to stay in sky that is just as dark as the underside of the B-2 itself so that the aircraft remains difficult to detect visually.
Radar EMISSIONS from the B-2 might also be detected, so the B-2 has an active radar that gradully ramps up in strength JUST ENOUGH to detect it's target, then gradually reduces it's output as it gets closer to the target. The radar system is so complex that a normal milling machine would take TWO YEARS to make ONE component of ONE radar for ONE airplane. Special machines therefore had to be designed to make the radar assemblies for the B-2.
The control surfaces on the wingtips open and close to steer the aircraft in yaw and keep the aircraft pointed forwards (the airplane is only nuetrally stable so is controlled by a quadruple-redundant fly-by-wire system). The problem is that moving these control surfaces increases the airplanes visibility on radar... differential computer-controlled engine thrust is therefore used to steer the aircraft when in "stealth mode". (A "Go To War" mode is selected in the cockpit to initialize this and other systems on the plane).
Almost every system in the B-2 is hardened against radiation that would result from a Soviet nuclear attack, as well as the from the explosions of the bombs dropped by the B-2 itself.
The B-2 naviagtes using both inertial-reference and GPS (Global Positions System) navigation systems, but inertial-reference system graudlly lose accuracy over time, and the GPS system could be made useless by destruction or jamming of our GPS satellaties. The B-2 therefore has an Astro-Inertial navigation system which uses fixes on stars to navigate. An electro-optical telescope mounted to the left of the cockpit detets stars and fixes the aircrafts position using these steller references. The system is sensitive enough to work in daytime, under a cloud cover!!! This and other systems allow the B-2 to detect, identify, and locate virtually any large surface target with NO outside help, under any weather conditions... something which NO other aircraft can do.
Flight-test of the B-2 (from first flight to first delivery) took 8 years.
