Blackstar to orbit? Aviation Week & Space Technology reports in its most recent issue that a two-stage-to-orbit system may have been declared operational during the 1990s. The Blackstar system appears to have heritage from three other X-Planes, the X-20 Dynasoar, the XB-70 Valkyrie, and the X-30 National Aerospace Plane. [Related MeFi post] [via]
So, why hasn't the Shuttle been replaced? Because it hasn't been easy. In the late 80's and early '90s, the cold-war-fantasy-cum-shuttle-replacement was the X-30 National Aerospace Plane (NASP) that was supposed to take off and land like a plane flying on super-fast Scramjet engines that, alas, were never really successful... In the late '90s, the New Economy, space-exploration-on-VC-money shuttle replacement was the X-33 VentureStar program which was eventually cancelled, after a long and turbulent history. The X-33/VentureStar was one of the most technologically daring machines ever built --albeit too daring. I cannot mention the X-33 without mentioning the ingenious-but-untested linear aerospike engine that was going to take it to orbit. If the US is now (again) considering a Shuttle replacement, maybe the Delta Clipper is worth a second look. The DC-X was a competitor for the X-33 program that was eventually scrapped, for technological and other reasons. At least the Russians and Europeans liked it so much better than the other New Shuttle options that they copied it.