Nerva became emperor immediately after Domitian’s murder in 96 AD. He had a lifetime of service to Rome and its emperors, and had served as consul twice, in 71 and 90 AD.

Six NERVA technology demonstrators were built between 1964 and 1973. The highest power threshold NASA could muster during testing was a scarcely believable 246,663 newtons (55,452 lbf) of thrust ...