stealth technology, designs and materials engineered for the military purpose of avoiding detection by radar or any other electronic system. Stealth, or antidetection, technology is applied to vehicles (e.g., tanks), missiles, ships, and aircraft with the goal of making the object more difficult to detect at closer and closer ranges. Since radar is the most difficult form of detection to elude, avoidance is generally accomplished by reducing the radar cross section (RCS) of the object to within the level of background noise; for example, the reported goal of U.S. military designers is to make a fighter plane with an RCS the size of a bird. The RCS is the area of an imaginary perfect reflector that would reflect the same amount of energy back to the receiving radar antenna as does the actual target, which may be much larger or even smaller than the RCS. A pickup truck, for example, with its flat surfaces and sharp edges has an RCS of approximately 200 sq m, but a smooth-edged fighter jet has an RCS of only 2 to 4 sq m. The RCS of any given object, however, differs at various angles and radar frequencies. Much about stealth technology remains classified, but among the antidetection techniques used in the U.S. Air Force F-117A Stealth fighter (now retired) and B-2 bomber were a low profile with no flat surfaces to reflect radar directly back, the intensive substitution of radar opaque composites in place of metals, and an overall coating of radar absorbing material. The implementation of stealth technology may require such compromises as reduced payload capacity, aerodynamic instability, and high design, production, and maintenance expenses. More recently, stealth technology has been incorporated into planes with a more traditional appearance than the F-117, such as the U.S. F-22 Raptor and the Russian-Indian Sukhoi T-50 fighters. China also is developing stealth aircraft.