Jupiter Family is pixiv's nickname for Otacon, Snake and Sunny.

At the end of MGS1, if you get the Otacon ending, Snake and Otacon have a brief conversation and make a reference to Space Odyssey.

"I'm David, Otacon."
"I'm Hal, Dave."
"Hal? Maybe we should take a trip to Jupiter."

Thus, the name. Messily drawn on purpose, also in a hiimdaisy-style.