The speed with which technology advances, and makes older stuff obsolete, has increased over the last decade. Big budget projects, with long development times, are increasingly at risk. This is particularly the case when electronics are involved. In the case of the Backscatter radar, smaller, portable, systems have since been developed as well. One reason backscatter radars are still useful is because they can detect most current stealth aircraft.
Another expensive Cold War era system is finally being retired. In this case, its a radar (the AN/FPS-118 Over-The-Horizon-Backscatter Radar), which was built to detect aircraft (Russian bombers carrying nuclear bombs and missiles) 3,000 kilometers away. After fifteen years of research, two of these systems were built in the late 1980s. They came online just as the Cold War ended. Total cost of the project has been about $1.5 billion. The Oregon radar was mothballed after one year of operation, while the one in Maine continued to operate for a few years to see if it could be of any use in detecting narcotics smugglers. This didnt work out, and the Maine facility was mothballed as well. This meant that the system could be put back into working order in about 24 months. Finally, it was decided that the two radars would never see much use, and have been ordered dismantled. This will be a big job, as each radar system consists of about five kilometers of tall metal transmitters/receivers, plus support and operator facilities. Each radar puts out about a megawatt of energy when in use. New technologies, particularly satellite based, has also contributed to making the backscatter radars obsolete.