In the Rogue One film, Galen Erso sent a message to Saw Gerrera and the rebels, in which he has revealed that the Death Star has a serious backdoor vulnerability: shoot a torpedo into the reactor and the whole Death Star will get overloaded and explode. A New Hope proved that Galen was right: Luke shot the torpedo and indeed the Death Star exploded.

But Galen also instructed the rebels that they should get the plans of the Death Star from the imperial citadel on Scarif. Why was this necessary? Wouldn't it have been better if Galen told in the same message which hole on the Death Star it is where the rebels have to shoot the torpedo to the reactor, and just ignore the plans altogether? Getting the plans from an imperial complex was dangerous, and Galen would surely have anticipated that danger.

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    I was thinking that. Don't forget though that it's a bloody big station, merely saying that it's somewhere on the meridian trench is like me telling you that there's buried treasure somewhere in Belgium
    – Valorum
    Commented Dec 19, 2016 at 21:23
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    @Valorum roughly 8 Belgiums, actually. A sphere with an 87 mile radius has roughly 95,000 square miles of area. Belgium has roughly 12,000.
    – user40790
    Commented Dec 19, 2016 at 21:32
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    @Axelrod Limiting it to the trench would reduce the search area to smaller than the entire surface area. If we had the width of the trench then perhaps we'd be able to say definitively, and search an area the size of Luxembourg.
    – Erik
    Commented Dec 19, 2016 at 21:36
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    @Axelrod according to Valorum's comment yes. I have no clue as far as the movie goes because I haven't seen it. Although I'm somewhat sad I didn't have a shovel with me when I was in Belgium now that Valorum told me there's buried treasure there...
    – Erik
    Commented Dec 19, 2016 at 21:46
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    Mostly, so Weird Al could rhyme "plans" - "hands". Commented Dec 20, 2016 at 4:59

7 Answers 7


According to the official novelization by Alexander Freed, he didn't know how to get the explosion to the reactor, only that it needs to be exploded:

Galen snapped back into focus, no longer hesitant or soft. “Saw, the reactor system, that’s the key. That’s the place I’ve laid my trap. It’s unstable, so one blast to any part of it will destroy the entire station.
You’ll need the plans, the structural plans, to find your way, but they exist. Sabotage from the inside is impossible: Krennic is too paranoid. But I’ve thought about this, Saw, prepared everything for you I could.”

And he clearly didn't have access to engineering plans to the whole station himself, being just in charge of the weapon. He knew where plans existed but didn't have access himself (else, he'd have said Eadu has them too, or as you said, would have sent them with the pilot):

“I know there’s at least one complete engineering archive in the data vault at the Citadel Tower on Scarif. Use what I’ve told you, run the analysis, and you’ll be able to plan your attack. Any pressurized explosion to the reactor module will set off a chain reaction that will-”
(Chapter 6)

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    He did at least arrange for there to be an exhaust port. Among other things, it’s referred to as “some trivial adjustment of Galen’s.”
    – Adamant
    Commented Dec 20, 2016 at 3:20
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    @Adamant - yeah, there was along trail of memos in novelization covering that. It looked too much like email at work so I skilled reading them :) Commented Dec 20, 2016 at 3:42
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    @b_jonas I'm not sure why it seems like such a stretch that someone could know a project's codename without also having the actual plans. I know of Area 51, but I'm pretty sure I'd be shot if I tried walking in there. Similarly, I know AMD is working on a GPU codenamed Vega, but I don't know many details other than that it's supposedly a higher end part, and I'm pretty sure AMD would not just hand me the complete technical documentation.
    – 8bittree
    Commented Dec 20, 2016 at 17:20
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    @b_jonas: I know your codename "b_jonas" but literally nothing else about you. So, y'know. Commented Dec 20, 2016 at 18:33
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    He just didn't know the codename was Stardust, Galen was responsible for the codename itself (the nickname given to his daughter).
    – tylerwal
    Commented Dec 21, 2016 at 21:52

There were two parts to the Rebels destruction of the Death Star. The first was the knowledge that the reactor was unstable, that any explosion there could cause a chain reaction. That was the easy part.

The second part was that there was a tiny vulnerability, a way to get ordnance down into the core to trigger that explosion. To find that vulnerability, the Rebels needed the plans.

Without the plans, they would have had no way to exploit the weakness Galen revealed. Without the weakness, they'd have had no idea what target to look for in the plans.

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    I can't believe we all forgot that the connection between the vent and the reactor wasn't spelled out. Good catch!
    – user40790
    Commented Dec 19, 2016 at 21:59
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    @Terriblefan: isn’t that the actual question, why it wasn’t spelled out?
    – Holger
    Commented Dec 20, 2016 at 9:55
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    @Holger Maybe it was, but the message was cut off, and since the message was destroyed/left behind it may have been a moot point. Could you remember latitude/longitude coordinates or whatever star warsian characters use after only hearing them once?
    – SethWhite
    Commented Dec 20, 2016 at 15:27
  • @SethWhite I remember the movie had a K2SO referencing this. Not sure what the exact quote was, though. Commented Dec 21, 2016 at 14:32
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    @DavidStarkey yeah, K2 literally said to Jyn "Your words were - one blast in the reactor, and the whole station goes to hell". Not exactly specific.
    – Petersaber
    Commented Dec 30, 2016 at 8:30

He did not have the technical details to give or else he would have. He was working as an administrator of a kyber crystal refining operation. He worked on the reactor design and was able to create the thermal exhaust port weakness, but that does not imply that he had access to the final architectural schematics. In fact, it is pretty clear he didn't as if the plans were available anywhere easier to get to than Scarif he would have said that. So when he submitted his part of the designs the vent was probably just a line drawn on a circle. So he knows the vent exists, but without the final plans he does not know the coordinates of the vent on the Death Star. Even if he had a general idea from, say, seeing the designs in a meeting, that would probably not be good enough for the sort of fast precision strike needed.

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    The weakness Galen created was not the exhaust port. The weakness he created was the instability of the reactor.
    – Werrf
    Commented Dec 19, 2016 at 22:09
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    The novelisation indicates that Erso was very well aware of the flaw with the reactor vents. He deliberately caused a critical failure in the Death Star's reactor design, then left it too late to resolve it through any other means than cutting holes in the shielding and allowing the radiation to vent to the surface. He was also aware of their position as he was able to confirm that they were nowhere near to the officer's quarters.
    – Valorum
    Commented Dec 19, 2016 at 22:23
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    additionally, the pre-movie novel "Catalyst" reveals that much of the station was built many many years prior to Erso being brought back into the fold by Krennic (shown in the film) to complete the weapon. The platform itself was done in a relatively short time. It was the weapon that took so long. This also explains why the Death Star II was so quickly built - the R&D had been done and it was just a matter of assembly.
    – NKCampbell
    Commented Dec 19, 2016 at 22:25
  • @HamHamj I believe that as an engineer Galen had access to the plans of the Death Star. He knew that the code name for the plans was "Stardust" after all.
    – b_jonas
    Commented Dec 19, 2016 at 23:05
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    I join b_jonas; I'm assuming that since the file is called stardust, he wrote the file, so he's more than just the refiner, he created the plans Commented Dec 20, 2016 at 14:09

A common sense answer here is that Galen didn't have the exact plans on him, of course, so he would have had to describe it from memory. Keep in mind the Death Star is the size of an entire moon. And as we see in ANH, its surface features look pretty much the same everywhere. So, it'd probably go something like this:

Galen: "So...what you need to do is, you see...so there's a trench somewhere on the north-east hemisphere that leads to the weakness. Well, there's about seven thousand trenches there, but you want the one that's...well it's near a tower. One of the identical four billion towers. Also, there's an exhaust port, but THIS ONE goes to straight to the reactor. Oh, but there's also about seven hundred thousand exhaust ports in that section. Hmm...you know what. Just go get the plans, it'll be easier."

The rebels didn't have time to fly around the Death Star looking for the right port, just shooting into every one they saw to see if it stuck. They needed to know exactly where to go, immediately, or risk getting annihilated before the plan would work.

  • I believe Galen had years to prepare for this thing before he sent the message. He even says "I arranged everything".
    – b_jonas
    Commented Dec 20, 2016 at 16:34
  • I don't believe Galen was in charge of the whole project. So even if he had years, if he didn't have access to exactly where the exhaust port would be in the schematics (which could, and probably did, change locations frequently as the engineers tried undoubtedly to find a workable solution to the error), he would have had to try to roughly explain the location of something he knew must exist, without knowing exactly where. So he probably didn't have years to find its exact location, since the whole Death Star plans, complete with faulty exhaust port, wasn't available to him at the start.
    – TVann
    Commented Dec 20, 2016 at 16:55
  • I find this explanation unsatisfying. I live on a planet the size of a planet, but I routinely give people directions to important locations without any difficulty. This is literally the most important fact in the galaxy, he has spent his entire life painstakingly introducing this flaw into the design, but in order to exploit it, he assumes that the rebels will be able to sneak onto a heavily guarded base and steal a gigantic data file and then somehow analyze all that data, find the flaw, and exploit it. [continued] Commented Dec 21, 2016 at 2:57
  • In other words, he was relying on all of the events from the last 30 minutes of Rogue One and the whole of A New Hope to occur, and to turn out exactly as well as they did. Commented Dec 21, 2016 at 2:58
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    @Malvolio You also give directions to people who live on the same planet, have for their entire lives, and are probably already (relatively) nearby to begin with. Plus there are tons of resources at your and their disposal to reference your directions. Imagine giving directions to someone with no map or internet, who has never even seen the Earth, who is coming from the other side of the galaxy. Now imagine doing the same thing if the entire earth looked like a corporate parking lot.
    – TVann
    Commented Dec 22, 2016 at 14:29

The real-world situation is this:

In the 1977 film, there was never any indication of a deliberate weakening of defenses. The rebels stole the plans in the hope of finding an accidental weakness, and found one.

Once Star Wars became the best film evah, and subject to endless analysis by people who analyze movies instead of getting laid, this sequence of events began to seem rather implausible. The builders of the Death Star were unable to find the flaw, despite decades of intimate familiarity with the plan, but the rebels were able to uncover it in just a few hours?

When the new film came out, the producers wanted to patch the problem: in the revised story line, the weakness (the unshielded "thermal exhaust port") was deliberately introduced to the design and deliberately disclosed to the rebels. None of this was mentioned in the previous movie, but neither was it contradicted.

There is still a problem, albeit a smaller one. The natural behavior of the saboteur, Galen Erso, would be to commit the location of the weakness (and whatever other information necessary to exploit it) to memory, or at worst, to some summary form, and pass that information along directly.

Of course, if the screenwriters allowed their character to do that, A New Hope would be retroactively made pointless, and they wouldn't have much of a story for Rogue One to boot. Instead, Erso carefully creates the weakness and only passes along enough information to tell the rebels what to look for in the plans, which the rebels need to obtain for themselves.

Had I been the screenwriter, I would have made Erso's plan to be the sensible one: to tell the rebels, "If you put an torpedo down the unshielded vent at 38.061927°N, 122.652542°W, the whole thing will blow up."

Then, of course, I'd kill off Erso before he could convey the details and give Jyn a line like "Alas, my father died before he could give us the exact location of the hole in the Imperial defense! Wait, the hole must be in there somewhere. If we analyze the plans carefully, we can find it. All we need now is to steal the plans."

  • @user23715 -- nice to see that the effort I put into picking a lat-long was not unappreciated. Commented Dec 22, 2016 at 15:58

It was necessary for purposes of data security. Galen made the rebels aware there was A vulnerability. If the message had fallen into the wrong hands (a third party who could sell the vulnerability back to the Empire) then all would have been for naught and the empire could dish out credits to the vendor and then patched the hole. Instead, he gives clues that really only the rebels could leverage which wouldn't be valuable to anyone else. The rebels could retrieve the information themselves and know all the details without anyone in between potentially being the wiser.

They call this a handshake in tech circles. I suspect similar patterns of communication are common in tradecraft as well.

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    I don't understand that. If someone gives the Empire the secret message, then the Empire can access the plans and figure out the vulnerability themselves.
    – b_jonas
    Commented Dec 20, 2016 at 20:22
  • I don't buy it. Even as it was, the Empire had access to two pieces of information, (1) that Jyn, a rebel, spoke to her father, a designer of the Death Star, and (2) that Jyn immediately went and stole the Death Star plans. The obvious conclusion is the designer told the rebel there was something of interest in the plans. It is now vital therefore to retrieve or destroy the stolen plans and find out what the rebels were looking for. Had Tarken not been such a thoroughgoing psychopath, he would have captured Jyn and asked her, hard, what she was looking for. Commented Dec 21, 2016 at 14:36
  • So if Galen revealed the exact location of the port in his message and the message fell into the hands of some extortionist, how exactly would they go about extorting the Empire? Odds are, if they don't have manpower to launch an assault on Scariff, they don't have the manpower to launch an assault on the Death Star either so that information is still useless to them. The best they could do would be to threaten to sell the message to the Rebels, which would work equally well regardless of what the message said.
    – aleppke
    Commented Feb 1, 2017 at 2:31

After reading all these comments, I had a great epiphany. Erso was in charge of only the superlaser, not the whole Death Star. He embedded the unstable reactor as his trap but did not know how to exploit it. The vent was a coincidence or a result of the reactor needing it, as requested by Erso. However, he did not know how the vent would be built or where it would lead to on the surface. Thus he told the rebels to get the plans and find a weakness for themselves.The imperial records on Scarif contained the entire engineering plans for the Death Star, codename "Stardust". Since the planning and building of the Death Star began long before Erso joined to build the superlaser, "Stardust" as the codename for the Death Star PRECEDED Jyn's nickname. So Jyn was named after the Death Star...

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    Can you show any sources for what led you to have this epiphany?
    – Edlothiad
    Commented Apr 22, 2017 at 5:44

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