How did the Rebels find the design flaw to the first Death Star?

Question

So I just read the answers to this question, where most of the authors agree complete fault analysis for a ridiculously complex project like the Death Star is close to impossible, given technical difficulties and bureaucratic nightmares. As a follow-up question:

When the Rebels were handed the Death Star plans by Princess Leia, they were able to find the flaw while a doomsday machine was on the way and predicted the effects of exploiting the fault accurately. How were they able to find it so quickly and efficiently? Mind I don't ask why the Empire engineers seemingly overlooked it, that's covered. But what method could the Rebels possibly have used? The Deus ex machina analysis engine with two parameters, maximum destruction and minimum material cost?

An in-universe explanation would be nice.

Answer 1

The Rebels had a slight advantage: they already knew what they were looking for; Galen's message, relayed by Jyn, explained both what to do, and what the result would be:

"What kind of trap?" [Baze] asked. "You said your father made a trap.”

"The reactor." On this point Jyn was utterly certain. "He's placed a weakness there. He's been hiding it for years. He said if you can blow the reactor — the module — the whole system goes down."

^{Rogue One: A Star Wars Story - Official Novelization Chapter 9}

This conversation occurs during the flight from Jedha to Eadu; she later recounts the message to the Rebel Council before the mission to Scarif. So the Rebel's analysts knew they were looking for a way to get an explosive into the reactor module, which is somewhat easier than starting from scratch.

Exactly how they located the specific exhaust port isn't described in great detail, but we know from the Alan Dean Foster novelization that it involved both computer and human analysis:

Little Artoo Detoo rested comfortably in a place of honor, his body radiating computer and data-bank hookups like a metal hairdo. On an array of screens and readouts nearby the technical information stored on the submicroscopic record tape within the robot's brain was being played out. Hours of it - diagrams, charts, statistics.

First the rush of material was slowed and digested by more sophisticated computer minds. Then the most critical information was turned over to human analysts for detailed evaluation.

^{Star Wars - Official Novelization Chapter 11}

Based on Foster's prose, we can imagine that the Alliance used their computers as a kind of sieving mechanism to reduce the search space, so the human analysts weren't wasting their time flipping through air conditioner specifications, or whatever.

Answer 2

The film's official novelisation actually gives us a pretty solid idea of how they found the flaw. Galen offered some direct advice to Jyn on how to attack the 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.”

The roar was growing louder. The stone seemed to tremble and Jyn fell to her knees, a shock of pain driving back the darkness of the cave long enough for her to realize that Saw, too, was shaking. His cane tapped rapidly on the floor. “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—”

And we also see some of the documents that they recovered from the disk, most notably...

SUPPLEMENTAL DATA: BATTLE STATION ENGINEERING NOTES

[Document #YM3884L (“Waste Radiation Distribution Solutions”), timestamped approximately eighteen months prior to Operation Fracture, sent from Engineering Operations Manager Shaith Vodran to Galen Erso.]

...

Option three: construction of manual venting shafts and thermal exhaust ports. This should reduce particle buildup to within tolerances but not to a degree I find personally acceptable. In addition, adding venting shafts risks additional incompatibilities with noncritical systems. Please alert me if you have concerns.

The ability to search for any documents that tied Erso, shafts and the station's main reactor together would have dramatically lowered the time needed to search for weaknesses.

Answer 3

Legends answer

According to The Movie Trilogy Sourcebook, one of the sourcebooks for West End Games' Star Wars RPG, General Dodonna was in charge of looking for a vulnerability, and came up blank until he remembered The Hobbit a legend about an invulnerable dragon with a hole in its armor. This inspired him to look for smaller, more easily-overlooked weaknesses.

At first, the situation seemed hopeless, as the station's defenses exceeded Dodonna's worst fears; the only strategy he could conceive that stood any chance was crashing wave after wave of the Alliance's heaviest vessels into the station, on the slim chance there would be sufficient damage to neutralize it; this would effectively destroy the Rebellion, but would allow a new one to grow without the Death Star threatening them. Dodonna prepared to go to sleep, but instead wandered the halls for fresh air. While doing so, he encountered a small child, weeping over a nightmare about a dragon coming to burn her village. Dodonna comforted her with an old tale of a Jedi Knight finding a hole in the dragon's scaly armor, killing it. Inspired, Dodonna ran back to his quarters and scoured the plans for a similar hole, eventually finding one in the form of a small exposed thermal exhaust port that led directly to the main reactor.

(source: Wookieepedia)

Answer 4

The rebels knew that the station's weakness was in the reactor, and they knew they'd need to target it from the outside. This narrows the search tremendously.

A torpedo is not going to navigate sharp bends or pass through obstacles such as heavy metal grates. Once they had the schematics, they could start from the reactor and follow every pathway leading away from it. Any path which had a sharp turn, dead end or obstacle could be eliminated. A wide, straight, open path leading to the station exterior would stand out very clearly.

The only other option would be to find something explosive next to the reactor that could be used to start a chain reaction. If they found something like that, it would just create an additional starting point to search. They'd still need to find a clear path to the station exterior.

Answer 5

You don't even need evidence from books and movies. Today, law firms use eDiscovery tools that can search millions of documents for this kind of information. The tools are pretty thorough. Given the technology we see in the Star Wars Universe, we can easily imagine they have even better tools. Some reasons why the Empire might not have found the flaw are:

• The expected their security apparatus to discover traitors.
• The perplexity of finding any system of catastrophic flaws is far greater than for one specific one.
• The flaws were documented, but in a way that obscured them, not obvious until you went looking for them.

Look at how teenage hackers are able to penetrate NSA, CIA, and DOD computer systems, and those are checked all the times for flaws.

Answer 6

The Rebels were able to accomplish the 'analysis' due to the fact the Death Star is, if anything, advanced technology, the construction of which is made possible only by the existence of an equally advanced and technically competent supporting society and culture, the size and scope of which would be large and well established. The freedom fighters constituting the 'Rebellion' are merely citizens of the Empire whose ideas on government are a bit outside the average citizen (and, of course, with the guts to do something about it). Thus, an analysis of the Death Star would be little different than a similar analysis performed by the engineers 'working' for the Empire. Nothing a few, creative, engineers driving in reverse couldn't crack.

Answer 7

They Didn’t?

If you watch the scene in the movie where the pilots are briefed on the Death Star plans, you see that the blueprints show this:

The actual Death Star looks like this:

Those plans are not correct. One obvious difference is that the blueprints show the equatorial trench running through the middle of the main dish, whereas the real Death Star has its dish slightly above it.

Although Jyn guessed that her father chose his pet name for her, “Stardust,” as the code name for the Death Star plans, her assumption was clearly mistaken. The plans that she stole, codename Stardust, must have been a rejected proposed redesign of the Death Star plans. It could not have been the original version, since we saw a blueprint that looked closer to what was built in Episode III. (If Galen Erso ever had a bastard child, he might have named the design the Imperial brass and bureaucracy and the rest of the committee got their fingerprints on after her.) By good luck, the Achilles’ heel from Stardust made it into the final design. But luck it was.

The Real-World Explanation

The CGI animation was the work of by Larry Cuba and others at the Circle Graphics Habitat at the University of Illinois at Chicago, later renamed the Electronics Visualization Laboratory (EViL).

The anonymous, unsourced claim made on Wookieepedia that the CGI was done at the Jet Propulsion Laboratory and left uncredited so as to prevent the artists’ employers from finding out they’d done it on work computers is completely false. Larry Cuba does have a screen credit for “computer animation and graphic display,” although his collaborators and the university do not. The institution was fully aware of the project and uses the fact that it did the CGI for Star Wars heavily in its marketing to this day.

This documentary by Cuba describes the process. As he explains (at 1:15), the Death Star model had not yet been constructed, so he was working from a matte painting in which the dish was in shadow as his reference.

The original PDP-11/45 that created the wireframe model of the Death Star is still up and running fully operational (with video of the old-school minicomputer).

Out-of-universe, and probably in-universe as well, the plans depict an earlier concept of the Death Star, different from what was constructed.