The Argonauts were known as strong and brave heroes from Greek mythology. These men got their name from the ship Argo that they used. Since these men were sailors on a quest, they got their name from the ship Argo which was used in their voyage. The term “Argonauts” is meant to mean "adventurer on a quest", so, by using this term, Stein is referring to being a voyager.
Information and picture retrieved from: http://theargonauts.com/about/what-is-an-argonaut.shtml
Information and picture retrieved from: http://theargonauts.com/about/what-is-an-argonaut.shtml