Setting a new movie in events that immediately preceded the first Star Wars film gives new filmmakers an amazing opportunity to create a new story in an existing world, but it also gives them a huge opportunity to answer a burning question about that story. We know that Rogue One: A Star Wars Story will deal with the theft of the Death Star plans, which are eventually used to discover a weakness that allows Luke Skywalker to blow it to pieces in Star Wars: Episode IV - A New Hope. (Spoilers. Sorry.) But does it really make sense that such a clear and obvious weakness would exist on such a massive project? It would if it was left there on purpose.
On its face, the thermal exhaust port that leads directly to the Death Star's main reactor, in a straight line no less, doesn't make a lot of sense. While there are certainly waste products that the station would need to expel, gasses don't require a straight line in order to follow a designated path, nevermind the fact that in the zero gravity of space, it wouldn't really work anyway. It's an incredibly convenient thing to exist. If it hadn't been there, the Rebellion would have been destroyed. Which may be why it was there.
We know that Galen Erso, the father of Felicity Jones' character in Rogue One, played by Mads Mikkelsen, is recruited by the Empire to help them build their ultimate battle station. While trailers have shown him going without a fight, it's also clear that he is going against his will. He's protecting his family by doing what the Empire wants of him. While doing anything overt that would hinder the production of the Death Star would surely get Galen killed and risk the lives of his family, certainly the existence of the Death Star itself also threatens them, so he might be willing to risk doing something that the Empire might not notice, like design a thermal exhaust port that runs directly to the main reactor.
Whatever skill set Galen has that makes him necessary to the Empire's plan is clearly somewhat unique. If there was somebody more sympathetic to the Empire that could do the job, they would use them. However, this unique knowledge or ability could also mean that the Empire wouldn't necessarily have anybody who could understand whatever Galen was doing, so he could create the weakness without anybody realizing what he was doing.
This could all be theoretical, however, in the most recent international trailer, we hear a couple of lines from Jyn Erso that makes us think this isn't just a theory. At one point, she says a couple of things that caught our ear.
While these two lines are spoken together in the trailer, the tone and inflection shift a bit, which makes us think that they may not be spoken that way in the actual film. However, they likely come during the same scene and the trailer clearly wants us to hear them together. How does Jyn Erso know that there is any way to defeat the Death Star? How does she know the plans are the key? She doesn't say there might be a way to defeat it if you look at the plans. She's not guessing or hoping. She clearly knows something here, and the entire reason she's brought in on this mission is because of her connection to the man working on the Death Star.
We're being led to believe that Jyn Erso hasn't seen her father since he was taken from her as a child. It's possible that the message that the Rebel Alliance "intercepted" from Jyn's father was meant for them to hear, and he's trying to get a message to them. It's possible that Jyn has heard from him somehow and so she knows more about the Death Star than we realize. It's also possible that she just knows her father, the sort of man that he is, and knows that he would leave something in the plans that the Rebels could use to fight the Death Star.
It's clear in Star Wars: A New Hope that the exact nature of the Death Star's weakness isn't known by the Rebels until the plans are analyzed at the base on Yavin. They're hoping to find something, they seem to believe they will, but they obviously don't know what it is or they wouldn't actually need the plans anymore. Why would they be so sure they'll get something out of the plans unless they knew there was something to find, and how would they know unless they had been told that there was?
We have a man working against his will, a woman with intimate knowledge of how that man works, and a Galactic Empire that apparently doesn't know enough to notice when their contractor builds a fatal flaw into their design. It all adds up to the simple explanation that the reason the attack run on the Death Star seems so perfect is because it was planned to be that way. Galen designed the beginning of the end of the Galactic Empire right under the Emperor's nose. 40 years ago we had no idea that Luke Skywalker's success was actually due to an act of industrial sabotage. Now we think it might. Do you agree?