Answer: a. He has already been to the asteroid.
Step-by-step explanation: in the given short text, Kenniston is telling his friend that they need to get back to an asteroid and that they only have two weeks to do that. He also says that they need a ship to accomplish their mission. From that excerpt we can infer that Kenniston has already been to the asteroid he is talking about, because he says "We've got to get back to that asteroid", if they need to "go back" it means that they have been there before.