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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.

b_jonas
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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 Dec 19 '16 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. –  Dec 19 '16 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 Dec 19 '16 at 21:36
  • @Erik But was the trench specifically designated as the location of the vent? :D –  Dec 19 '16 at 21:41
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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 Dec 19 '16 at 21:46
  • @Valorum I assumed that Galen knew enough about where the hole was that he could give a more specific location to the rebels. HamHamJ suggests in his answer that Galen might have known less than I supposed. – b_jonas Dec 19 '16 at 23:03
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    Mostly, so Weird Al could rhyme "plans" - "hands". – DVK-on-Ahch-To Dec 20 '16 at 04:59
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    @Terriblefan I'd bet good money that those X-Wing things fly a lot faster than Valorum walks, carrying a shovel and a metal detector. – Jon Hanna Dec 20 '16 at 12:11
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    One other reason I don't think has been mentioned is trust. The rebel's have little reason to trust Galen. If they have the plan however, stolen from the actual Imperial archive, they can run a simulation on it to confirm what he says. – yesennes Dec 21 '16 at 14:16
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    @yesennes: That might give a reason for the rebels to try to steal the plan anyway, but I don't think it's a reason for Galen to hold back details. – b_jonas Dec 21 '16 at 15:16
  • the Death Star is a 120km wide ball of fiery death, and without the plans, the Rebels would have no idea what to look for. It is likely that even if they found the 60km long vent, they wouldn't have guessed it was the flaw. – Petersaber Dec 30 '16 at 08:29

7 Answers7

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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.

Werrf
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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! –  Dec 19 '16 at 21:59
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    @Terriblefan: isn’t that the actual question, why it wasn’t spelled out? – Holger Dec 20 '16 at 09:55
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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 Dec 20 '16 at 15:27
  • @SethWhite I remember the movie had a K2SO referencing this. Not sure what the exact quote was, though. – David Starkey Dec 21 '16 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 Dec 30 '16 at 08:30
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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.

HamHamJ
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    The weakness Galen created was not the exhaust port. The weakness he created was the instability of the reactor. – Werrf Dec 19 '16 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 Dec 19 '16 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 Dec 19 '16 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 Dec 19 '16 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 – Andrew Magerman Dec 20 '16 at 14:09
  • @b_jonas He knows the plans exist, where they are, and was the one to come up with the codename to file them under. He may have clearance to go to Scarif and view them if he needs to for his own work. But he isn't cleared to remove them or copy them and would probably be closely monitored while he worked with them. – HamHamJ Dec 20 '16 at 15:10
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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)

DVK-on-Ahch-To
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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 Dec 20 '16 at 03:20
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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 :) – DVK-on-Ahch-To Dec 20 '16 at 03:42
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    Same comment as to HamHamJ: if Galen didn't have access to the Death Star plans, then how did he know their codename was Stardust? – b_jonas Dec 20 '16 at 09:23
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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 Dec 20 '16 at 17:20
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    @b_jonas: I know your codename "b_jonas" but literally nothing else about you. So, y'know. – Lightness Races in Orbit Dec 20 '16 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 Dec 21 '16 at 21:52
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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.

TVann
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  • I believe Galen had years to prepare for this thing before he sent the message. He even says "I arranged everything". – b_jonas Dec 20 '16 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 Dec 20 '16 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] – Michael Lorton Dec 21 '16 at 02:57
  • 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. – Michael Lorton Dec 21 '16 at 02:58
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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 Dec 22 '16 at 14:29
  • @Malvolio you give people directions to a 2 meter hole somewhere on the planet when you're not sure where that hole is? –  Dec 30 '16 at 08:16
  • Jeez, @TVann, what kind of corporation do you work at that the parking looks like this? And I am looking at a man-hole, noticeably smaller than a womp-rat, and I can locate it with three words. – Michael Lorton Dec 30 '16 at 16:46
  • @Po-ta-toe, why couldn't Galen just look and see where the vent was? I would assume an exhaust vent would have to be put in fairly early in the construction process. If Galen didn't have the access to find the vent, how could he be sure it was there? – Michael Lorton Dec 30 '16 at 16:47
  • @Malvolio he says he only knows of one full schematic, –  Dec 30 '16 at 16:48
  • @Malvolio not to get bogged down in chat, but since you seem to have missed my intention, what I was getting at in my comment and in my answer, was that the Death Star looks very similar all around, besides the dish and the equator (very industrial, with the same sorts of terrain all around). Without exact coordinates to give, simply describing the general location of a tiny (2 meter) feature on something the size of a moon that has uniform features and terrain all the way around (with no map or frame of reference to use in such description), would be practically impossible. – TVann Dec 30 '16 at 16:51
  • @TVann -- if I am understanding you, you mean that in the absence of a North Pole and a Prime Meridian, it's difficult or impossible to specify a location on an effectively featureless sphere. OK, but how does stealing the plans solve that? By describing enough distinguishable features, you establish a North Pole and a Prime Meridian? – Michael Lorton Dec 30 '16 at 16:58
  • @Malvolio Even with general descriptors like "prime meridian" or "west of the big dish" could only, even in the most optimistic scenario, narrow the search down to a section of several square miles, still far too large to search for in-the-moment. Having the plans is akin to having your map tool you linked to. Your three words make no sense to anyone without such a tool. But, give them a tool (i.e., the plans) and something to look for like a description (the weakness in question), and they can work out the rest. – TVann Dec 30 '16 at 17:01
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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."

Michael Lorton
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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.

Core
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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 Dec 20 '16 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. – Michael Lorton Dec 21 '16 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 Feb 01 '17 at 02:31
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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...

conspiracy
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