How did we lose the technology to go to the Moon? If it has been built, it can be built again, can't it? What exactly is the problem?
There are so many little details that never got written down in the blueprints, and were kept in the heads of the builders. There were seals that did not fit unless you got Mary with the tiny fingers to lube the seal with a little spit and use her little finger to seat the seal. The driver transistors that had to be selected from the top 10% in speed and the bottom 5% in leakage. The titanium pieces that had to be rinsed twice in distilled water in the summer when the water company puts more chlorine in the tap water. The exact pressure you had to use while drilling the holes in the injector plate to avoid skipping or gouging. The exact angle you had to clamp on the heating clamp and hold the electrode when welding the stainless steel bell to prevent warping. Probably thousands of other important details, all lost when those folks retired. The information was supposed to be kept on the blueprints, but sometimes last-minute changes were done by telephone and never made it into paper prints. There were also supposed to be assembly, build, and test documents, but in those days before word-processors, little details often did not make it into the official manuals. You don't even have to go that far back-- the nuke bomb makers lost some of the details on how to make some very special foam. They could do it in 1980, but lost the secret sometime after that.