Tell the guard that you are an inspector

"Surprise! This is an inspection, ordered by Colonel James Huddleton," you say determined, stepping just a little bit too close, as those guys usually do.

"Never heard the name," the guard answers.

"That's because it's top secret. There are many enemies that gather around the Zeta Sector. If we let them, they will tear us apart. For this reason we have a whole cadre dedicated to make sure that we are ready for them. This department is called the Sect of Thunder. Home of the sector's mightiest protectors."

"Right," the guard rolls his eyes.

"It's true!" you say enthusiastic.

"It's not," the guard sighs.

"Yes it is!" you add. But there is no answer.

And thus you have to wait until he takes a piss - guards are human beings too! -, so you can step closer to the ship, and start probing it for possible entry points.

Easy! you think to yourself, as you realize that one of the airlocks are still open. Through it, you can climb onboard easily, arriving to what is seems like the ship's engine room.

"Hey, what are you doing here?" the mechanic raises his head the moment he sees you.

Two other people quickly barge in. Looks like the captain made sure there would be sufficient personnel to guard his vessel. You certainly won't fool these guys. This means you will have to figure out something else.