The giant, 40-ft. space telescope resting in the airtight, climate-controlled clean room at NASA’s Goddard Space Flight Center in Greenbelt, Md., wants nothing to do with the microscopic dust particles clinging to your clothing. So before you enter the room, you stand in a chamber that blows high-powered, compressed air at you from head to toe, sweeping you clean. Next you dress up in surgical scrubs—booties, head covering, mask, blouse, and pants—and pass through a series of doors that take you into successively more sterile anterooms. Only then, when your dust can pose no danger to the delicate machine in the center of the room, can you join the Nancy Grace Roman Space Telescope on the factory floor. There, technicians are busy completing its assembly in preparation for its…