After completing the Mothership Zeta DLC, two of the characters: the cowboy and the other wastelander will leave the ship.

Sally, Operation Anchorage Medic and the Samurai will stay behind on the ship.

Sally will give you anything she finds on the ship after asking her to "Report" and return a day or two to resupply.

The Medic will supply you with weapons, and convert the alien biogel into a human version with more health points and no side effects. He can also make Cyro Mines from the Cryo Lab mission you brought him along for.

This can be replayed over as many time as you want and sell whatever you want for 300 - 1000 caps for each weapon sold.