Huygens was an amazing project. It also sticks in my head as a really instructive example of "bug in production code" - the Huygens probe was transmitting on two channels to the Cassini orbiter during its descent. Due to a mistake in the Cassini software, one of the receivers never got switched on. 900 million miles from Earth and during a one-off unprecedented probe landing on an outer solar system body. Half the images and some wind speed data lost.

I don't know if the exact details of the bug ever got published but it would be interesting to know how it slipped through testing.

JPL tests in production!