America's newest nuclear stealth bomber is making its public debut after years of secret development and as part of the Pentagon's answer to rising concerns over a future conflict with China. The B-21 Raider is the first new American bomber aircraft in more than 30 years. Almost every aspect of the program is classified. Ahead of its unveiling Friday at an Air Force facility in Palmdale, California, only artists' renderings of the warplane have been released. Those few images reveal that the Raider resembles the black nuclear stealth bomber it will eventually replace, the B-2 Spirit. The bomber is part…