Generally our articles on missions are on the missions themselves, their planning, accomplishments, and so on, with separate articles on the components describing the functioning of the components themselves. For example, the information on the first moon landing is on [[Apollo 11]], the name of the mission, while [[Apollo Lunar Module]], the craft that actually performed the landing, is an article on the craft itself (which of course does mention that it landed on the moon, but is not the primary article about the moon landing).
It seems to make sense, along similar lines, to have [[Cassini-Huygens]] be the article about the mission, which was planned and executed largely as a joint mission, and then separate articles about [[Cassini]] and [[Huygens]] describing the detailed information about the craft. After all, there was no "Huygens mission" or "Cassini mission", but a "Cassini-Huygens mission" that used both craft. Huygens and Cassini themselves are merely pieces of equipment.
-Mark