"That's no moon; it's a space station!"
With those immortal words, we were introduced to the Death Star — the most famous science-fiction superweapon of them all! Now, with the release of Rogue One, the story of the Death Star is finally complete. Tying together the movies and the novels, we now know the full story of that tremendous planet-destroying weapon!
Warning: Spoilers follow for Rogue One!
Back to the Beginning
The story of the Death Star begins back in Attack of the Clones, with the Separatists in possession of plans for the battlestation! It's only in James Luceno's novel Catalyst that we find the reason for this; it seems the Sith had long coveted the power to destroy entire worlds, and Palpatine hatched an insidious scheme to have the Death Star built.
The captive Geonosian leader, Poggle the Lesser, insisted that the Separatists had no project in the works. Still, Palpatine was able to use the Republic's fear to kickstart work on the project. If the Separatists were building such a superweapon, then it stood to reason that the Republic needed to get there first!
All of this was done in secret, with only a handful of Palpatine's closest military advisers aware of the project. Fittingly, Orson Krennic persuaded Poggle the Lesser's Geonosian hive to work for the Republic, and the Death Star was born over the skies of Geonosis.
The real problem with the Death Star, though, was with the superweapon itself. It was here that Orson Krennic's real genius demonstrated itself; he remembered an old friend, Galen Erso. Erso was a backwater scientist with incredible intelligence, and expertise in the use of Kyber Crystals. Krennic began manipulating Galen and his wife Lyra, working to make them indebted to him. Krennic's real masterstroke, though, came when the Republic became the Empire; he persuaded Galen that Palpatine was focused on using Kyber to create a cheap, sustainable power source that would bring peace to the Galaxy.
Galen and Lyra fell for Krennic's lies, and as a result Galen began working to unlock the power of the Kyber Crystals. Unknown to Galen, his research was being co-opted into the Death Star project, with entire worlds ravaged when Imperial scientists were unable to reverse-engineer his discoveries and technology.
The Construction Continues
The years passed, and the Republic became the Empire. Wilhuff Tarkin rose to influence, espousing a doctrine that matched Palpatine's own: the belief that a strong military was essential to galactic peace. Tarkin believed that peace could only be achieved through fear, with the Imperial war machine possessing unstoppable military might. The Death Star would be the greatest instrument of fear of them all.
In John Jackson Miller's novel A New Dawn, we learn that the Tarkin Doctrine had an unexpected repercussion. Building Star Destroyers takes a vast amount of raw material; so does building the Death Star. As entire worlds were razed for ore, as planetary populations were decimated by the Empire's lack of concern for environmental regulations, the seeds of Rebellion were sown. As we saw in James Luceno's Tarkin, the Death Star was moved to orbit around Scarif, where the final construction took place; many small splinter groups learned of a secret engineering works, but the truth about the Death Star didn't leak out.
Galen Erso's Betrayal
As we saw in Catalyst, Galen Erso's wife Lyra became suspicious of Krennic's motives. The Ersos ultimate discovered the truth about the Death Star, and fled with their daughter Jyn. Rogue One opens with Krennic discovering the Ersos; Galen was captured by the Empire, Lyra was killed, but Jyn escaped.
At first Galen resisted working for the Empire, but he quickly discovered that the Imperial scientists would ultimately unlock the power of the Kyber Crystals. He decided to position himself to sabotage the Death Star, and over many years, he earned Krennic's trust once again; Krennic had always tended to underestimate Galen, believing Lyra to be the troublesome one.
As the years passed, Erso introduced a weakness into the Death Star's design. He ensured that the Death Star's reactor was dangerously unstable, and that a single explosion would lead to a chain reaction. The Rogue One novelization, by Alexander Freed, confirms that he manipulated Imperial bureaucracy to create the infamous exhaust port - a perfect way to launch a missile into the Death Star. Erso leaked knowledge of the Death Star to the Rebellion, and sent a message to his daughter Jyn that he'd introduced this weakness.
Rogue One tells the story of the Death Star plans — and of the band of rebels who raid the planet Scarif to steal the plans. The full might of the Empire is brought against the rebels, but the plans still escape; and that leads us directly into the events of A New Hope; the destruction of Alderaan; and, ultimately, Luke Skywalker's successful attack on the Death Star.
We finally know the history of the Death Star. Weaving between novels and films, the now know that the Emperor manipulated both the Republic and the Empire into constructing the Death Star. We know that the superweapon itself was the product of Galen Erso's genius - and that the critical weakness was a deliberate one. Rogue One may not tell the tale of the Skywalker family, but it certainly fits brilliantly into the overarching Star Wars narrative!