4 ms·

Someone mentioned them in this discussion ~30 minutes before you posted.

• dTal 10y ago
  Where? I'm ctrl-f-ing here and seeing nothing older than my comment.
  • greglindahl 10y ago
    OK, the previous ref was for nuclear pulse propulsion, which I'm sure you consider completely different.
    • dTal 10y ago
      They are extremely different. One is a highly impractical idea from the 1940s, and the other is a relatively recent and promising design that continues to be refined.
      • m_mueller 10y ago
        What's exactly impractical about a nuclear pulse drive - conventionally launched and activated outside the atmosphere? We know how to build that stuff safely to account for launch failures, it has been done with RTGs many times already.