Conversation so far:
When was the expedition?
In 1955-1956, Heyerdahl organized the Norwegian Archaeological Expedition to Rapa Nui.
Where did the expedition start from?
CANNOTANSWER.
How many people were on the expedition?
The expedition's scientific staff included Arne Skjolsvold, Carlyle Smith, Edwin Ferdon, Gonzalo Figueroa and William Mulloy.

Question: How long did the expedition take?
Self-contained rewrite: How long did the Thor Heyerdahl's expedition to Rapa Nui take?