How was construction of the Death Star(s) kept secret?

Question

According to various sources there were over 2,379,000 people on board the original Death Star when it exploded. On top of that it's said that it took 19+ years to build and millions of people worked on the construction.

Yet despite all of those people working on a massive project (and the 2 million personnel being transferred and living there!) people like Han Solo and Obi Wan have no idea about the Death Star. Even though Han is a smuggler who has a history with the Empire and it would be in his interests to know about it.

So my question is: How did the Empire keep the Death Star secret from the general populace and even from the underworld which would have a vested interest in that information?

In-universe answers please.

Answer 1

The canon explanation is given in the novel Tarkin.

The Empire used a combination of secluded and inhospitable bases which each supported only part of the project. This made sure no single person (except the Emperor and Tarkin) knew about the project as a whole.

The Death Star was constructed in orbit over the planet Geonosis, and the planet's irradiated surface discouraged anyone from even traveling to the planet. Geonosis was also heavily defended:

Harassment of Imperial installations by pirates and malcontents was nothing new, but in almost all cases the assaults had been hit-and-run sorties, and none had taken place so close to heavily defended Geonosis.

...

The epicenter of a bustling throng of construction droids, supply ships, and cargo carriers, safeguarded by four Star Destroyers and twice as many frigates, the deep-space mobile battle station hovered in fixed orbit above secluded and forbidding Geonosis. When viewed from mid-system or from even as close as the asteroid belt that further isolated the planet from celestial interchange, one could be fooled into believing that the irradiated world had added another small moon to its collection.

_{Tarkin, p. 25, 257}

Wilhuff Tarkin, who was in charge of the overall project, was stationed on Sentinel Base; this base was located on an extremely remote system that didn't even have name:

For those in the know, then, it seemed inexplicable that Wilhuff Tarkin should be assigned to a desolate moon in a nameless system in a remote region of the Outer Rim. The closest planets of any note were the desert world Tatooine and equally inhospitable Geonosis, on whose irradiated surface the Clone Wars had begun and which had since become a denied outlier to all but an inner circle of Imperial scientists and engineers.

_{Tarkin, p. 5}

A different base, called Rampart Station, served as the marshaling depot for supplies:

Coreward from Sentinel in the direction of the planet Pii, Rampart was a marshaling depot for supply ships bound for Geonosis, where the deep-space weapon was under construction.

_{Tarkin, p. 10}

The people who delivered supplies to this base had no idea what the supplies were for.

The Death Star's hyperdrive generator came from a separate base called Desolation Station:

There was probably no harm in sharing with Amedda information about the expected shipments of matériel from Desolation Station to Geonosis—including vital components for the battle station’s complex hyperdrive generator—but he was under no obligation to do so.

_{Tarkin, p. 29}

Although millions of individuals were involved in the construction of the Death Star, even Imperial Moffs could not see the whole picture and thus figure out what the Empire was actually constructing:

What bothered him was that, compliant with a strategy that no base commander—Moff, admiral, or general—should have unrestricted access to information regarding shipments, scheduling, or construction progress, no single person was in charge of the project, unless of course the Emperor was considered to be that person. But the Emperor’s visits had been few and far between, and it was anyone’s guess just how much information was getting past the Imperial Ruling Council the Moffs and others answered to and actually reaching the Emperor’s ear. Certainly he was being briefed, but briefings were no longer enough. The project had reached a point where it had to rely on countless suppliers; and though each was being kept in the dark regarding the final destination of their contributions, millions of beings, perhaps tens of millions of beings galaxywide, were now involved with the battle station in one capacity or another.

_{Tarkin, p. 27}

The Death Star was constructed using slave labor and recruited workers from nearby areas. These laborers were not in a position to tell anyone else about what they worked on.

For three years the only non- or near-humans he had seen or had direct contact with had been slaves or recruited laborers at outlying bases or at the battle station’s construction site.

_{Tarkin, p. 56}

The distributed network of bases involved in the construction meant that very few people knew what the Empire was actually building, and the workers themselves were not in a position to tell anyone what they were building.

Answer 2

In addition to the others, I want to put some of the numbers into scope.

Given this other question and answer, and using the rough order of magnitude of 100 Quadrillion (1x10^17, or 100,000,000,000,000,000).

Using your figure of 2,379,000, and the above galactic population, the amount of workers on the Death Star amounts to 0.0000002379% of the galactic population.

Taking the numbers from this question, we see that there are roughly 50,000,000 inhabited planets in the Empire. Which means on average one person from every 21st planet was pulled in to work on the project. And even that suggests an even distribution, which is obviously not true per Null's answer showing slave labor being a factor.

Others have noted the 'massive' amount of materials needed to make this thing come together, but the numbers would work out similarly for that as well. In the grand scheme of things, in a galaxy-wide community, the Death Star is a tiny and insignificant object. The amount of resources to build the Death Star is probably gathered and refined a thousand times over on an hourly basis.

Answer 3

In Disney canon

this has yet to be sufficiently explained.

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In Legends canon

The construction of the Death Stars were done in a secret installation called The Maw Installation.

This was a remote area largely inaccessible due to the surrounding black holes. Here, Tarkin had a number of scientists and construction crews secretly developing and building weapons such as the Death Stars, Sun Crushers and World Devastators.

Once complete, the weapons would be brought out from the Maw and deployed.

The Rebel alliance had heard of the installation, but could never find it, or learn exactly what was being done or worked on there.

Answer 4

So long as you don’t mind no-longer canon works, then I recommend reading “Star Wars : Death Star” by Michael Reaves and Steve Perry. Long story short though, they didn’t (“Help me Obi Wan Kenobi – You’re my only hope”).

They did keep it a secret for a good while though, and their go-to plan was to kill everyone and everything that had any possible way of knowing what was going on. All of the construction was done in a backwoods star system with only one inhabited world, and that was a prison world. Anything non-imperial that tried to get in or out was blown to bits. Also when they left they hyper-matter-gunned the prison world – just to be sure.

Answer 5

Easy, although Star Wars occurred long ago in a galaxy far far away, a galaxy is a huge (edit: mind bogglingly vast) expanse of space, and no one was trading with the Ewoks, who revered 3CPO as a god because the last time they saw a droid was sometime long ago passed down through oral history.

The question is analogous to how come nobody noticed that red grain of sand on this white sand beach despite the fact vacationers have been coming to this beach since the beginning of recorded history.

Answer 6

Yeah. The fact is, Vader can be everywhere. The only people who could leak info would be killed. Doubtless personal communication was blocked on the Death Star. Thus, only those getting materials could have a shot at leaking any info, and they would have been promptly disposed of.