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In the Star Wars saga, one of the most iconic weapons of the Empire was the Death Star: a self sustained weapons platform the size of a moon, with the capacity to destroy a planet. in A New Hope, we see the first Death Star in close proximity to the planet Alderaan, holding the planet hostage as the Empire tries to deduce the location of the Rebel Alliance's headquarters. In Return of the Jedi, we see the second Death Star in "dry dock" over the forest moon of Endor as it is being constructed.

My question is: How did the Death Star move? I imagine a spherical space station the size of a moon would be utterly massive, requiring a massive amount of thrust to move it. If it was constructed in low orbit of an inhabited planet/moon, the gravitational field would be immense, consisting of the planet/moon's gravity, and the Death Star's own considerable gravity. Breaking that gravitational field would be a massive task, yet we see no thrusters or engines on either Death Star. Were they hidden, stored under the station's surface while not in use? Was the station towed by another vessel?

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Believe in force, Vader.. – Evil Angel May 30 '12 at 2:16
With a hyperdrive array. Duh. – Gorchestopher H May 30 '12 at 2:25
How does the Death Star move? ... any dang way it wants to. – Omegacron Aug 19 '14 at 18:42
up vote 32 down vote accepted

It depends on what level of canon you are looking for.

If you accept the Gaming books, the Death Star Technical Companion (at least one of them, I believe there were several) lists it as having both Ion drives and a series of 123 hyper-drive field generators. See chapter two, Technical Specifications.

Image from the Death Star Technical Companion (Image from the Death Star Technical Companion, 1st edition, published by West End Games.)

Given that the reactor was deep inside, we could well have been seeing the ports the Ion drives used, and never realized it. In most space vehicles that we see, the source of the propulsion is visible as it's close to where it's being emitted, and we see the burning / glow / whatever -- In the Death Star, the Reactor was deep inside. I believe the Ion output ports were inside that trench along the middle.

The Technical Companion says: "Finally, the surface was riddled with thermal exhaust ports, heat sinks, sublight thrusters, hyperdrive thrusters ... "

(Emphasis mine)

As I recall, there is also more on this in the expanded universe; the Death Star that we eventually see was the result of a fairly substantial evolution.

One thing to remember, though; the Death Star was HUGE. If you look at the picture I included, that Star Destroyer in the corner is to scale, and you may recall those things were huge, themselves. The Death Star was the size of a small moon; the thrust ports could be easily visible on the surface, and we still might not see them, as most shots of the Death Star show a larger portion of it's surface -- If there are a few hundred of them, and they are each say 500 meters square, we'd never notice them.

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Those are awfully big computers.... – DampeS8N May 30 '12 at 3:01
@KeithHWeston even assuming a width of 10 feet only, we are still talking 18 cubic miles of computer. (if that takes up 40% of the cross-section) I repeat, that's an awfully big computer. – DampeS8N May 30 '12 at 3:10
@DampeS8N - No argument.... I didn't design it, and I think it's pretty unrealistic, too. But (to play devil/Lucas' advocate) huge, even planet spanning computers were not an uncommon staple of sci-fi for a while; until the transistor and IC took over, the miniaturization process really couldn't happen. Out-of-universe, though, I think for the guys building the specs, "Computer Core" == "What in hell are we gonna call all of this extra space?!? Did Lucas consider how much VOLUME this thing had! GAH!" – K-H-W May 30 '12 at 3:14
@KeithHWeston Both answers were good, but yours was the only one to address why the thrusters aren't visible. You get the cigar. – Gabe Willard Jun 2 '12 at 21:18
It's really a 70s movie - computers sized half a moon! – n611x007 Jul 7 '12 at 8:54

According to Star Wars Technical Journal (Volume Two) (July 1994) (emphasis added):

At the core of the Death Star was an immense, cavernous housing for the battle station's power generator matrix. A fusion reactor of incredible proportions, fed by stellar fuel bottles lining its periphery, produced the raw energy demanded by the Death Star's superlaser and hyperdrive systems. Much of the station's interior volume was filled by the machinery necessary to sustain such a fusion core, with sublight propulsion systems and defense field generators lining the outer equatorial regions. Realspace propulsion was handled by an external array of powerful ion engines, which converted the raw fusion energy of the station's core into thrust and pressed the station's great mass into any motion dictated by the Death Star's huge navicomputer banks. While ion engines of such magnitude are highly radioactive, no other system could provide the directional control necessary for a station of such great size. Engineering personnel assigned to monitor ion vent operations usually wore radiation suits.

The Death Star's hyperspace motivator units were comprised of linked banks of field generators such as those found aboard Imperial Star Destroyers. One hundred twenty-three individual hyperspace generators, tied into a single navigational matrix, were necessary to carry the Death Star beyond the speed of light. The intense power generated within the battle station, combined with its great mass, gave it both magnetic and artificial gravitational fields equal to those of a natural body many times its size.

At the true equator of the station was a deep trench, encircling the Death Star like a straight, endless canyon some 376 kilometers in length. Here were housed the station's primary hanger bays, drive thrusters, heat exhausts, primary sensor arrays, and tractor beam systems.

It also adds the following statistics:

Construction site: Planetary orbit, penal world Despayre, Horuz system, Outer Rim Territories

Diameter: 120,000 meters (equivalent to a Class IV moon)

Maximum Speed: 1.2c

Fuel: Compressed stellar hydrogen

Here is an exterior diagram from the technical journal showing where the ion drives are located:

Death Star exterior diagram in Star Wars Technical Journal (Volume Two)

Here is a interior diagram from the technical journal:

Death Star interior diagram in Star Wars Technical Journal (Volume Two)

There is a nice full color multi-page cross section of the Death Star in Star Wars Incredible Cross Sections which shows the ion sublight engines and hyperdrive are hidden inside of the moon space station along the equatorial sector.

Death Star diagram in Star Wars Incredible Cross Sections

Below are close-ups on where the ion sublight engines and hyperdrive are located. Notice that they are hidden beneath the surface of the Death Star.

Cross section of the ion sublight engines

Cross section of the hyperdrive

The Essential Guide to Vehicles and Vessels (1996) states:

Fully half of the battle station's interior was filled by the reactor core, the sublight and hyperdrive systems and the superlaser housing.

Death Star picture from the Essential Guide to Vehicles and Vessels

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Many Bothans died to bring us this information. – benshepherd Nov 19 '15 at 12:18

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