But the question of whether the monitoring system and ban will work, in the end, is a political one. Each nation that signed the test ban treaty is now independently reviewing it against their politics and budget, deciding whether to ratify the ban and fund the IMS.

"The idea of the treaty and the monitoring system is to provide a credible deterrent to testing," says Zucca. "If you are a potential evader, the idea of this treaty is to make you think twice, or thrice, or four, or five, or six times." So in the end, the decision to build the sentinel will be based not just on whether its technology works, but as much on how technologically menacing it appears--from potential ground zero.