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In the Battle of Endor, the unfinished Death Star II was firing its superlaser at the Rebel capital ships while the ground team was still trying to disable the Death Star's shield. Which means the shield was still operational.

In multiple films (e.g. The Emptire Strikes Back, Rogue One), we've seen that both energy and projectile weapons are generally stopped by shields. In Rogue One, we've also been told that

a shield works both ways, i.e. that it's impossible to get out through a shield as well as impossible to get in.

That leaves me wondering: how was the Death Star able to fire through its shield while still being protected by it? Is there an in-universe explanation?

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    Where's that quote from; could it not be that "a shield works in exactly as many directions as the people operating it want it to operate
    – user20310
    Feb 27, 2017 at 15:54
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    @Angew For exactly the reason the people who are concerned about it being two ways are concerned about it being two ways. Military bases hate people sneaking in, but they aren't huge fans of people sneaking out either
    – user20310
    Feb 27, 2017 at 16:08
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    Shields behave inconsistently in Star Wars canon. In Legends, the Death Star shield would probably be explained as a particle shield that blocks physical objects but not blaster bolts.
    – Null ♦
    Feb 27, 2017 at 16:33
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    Death Star's superlaser is in phase with the shield... Sorry, wrong universe...
    – Ragnarok
    Feb 27, 2017 at 16:48
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    This question appears to assume that all shields are the same. However, humans almost always build variations of things in order to target specific qualities (reliability, cost, utility, specializations, etc). Perhaps one-way shields have larger power requirements or other complications. That kind of system might make sense on larger ships, but might not make sense on small ships (cheap, simple, disposable) or something on a planetary scale (already massive, problems scaling further up).
    – Ellesedil
    Feb 27, 2017 at 20:54

3 Answers 3

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The implication, at least according to the Death Star Owner's Technical Manual, is that the superlaser is sufficient powerful as to penetrate the shield, allowing a majority of the energy to pass through unhindered.

Built on the forest moon's surface, the SLD-26 planetary shield generator consisted of a dish network, an underground generator, and an above-ground shield projector complex that spanned an area of 70km (43 miles) in diameter. The planetary shield generator projected an energy screen that completely enveloped the orbital Death Star II, and could be easily defended bv anti-infantry and anti-vehicle turrets. The only weapon capable of penetrating the energy screen was a superlaser.

The shield presumably then regenerates after the trailing edge of the blast has crossed the shield barrier.

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  • I'm not sure that quote implies that, wouldn't firing on your own shields be a very bad idea (broardly equivalent to just lowering the shields). Isn't it just emphasising how strong the shields were
    – user20310
    Mar 1, 2017 at 9:22
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    @user20310 - I thought that, but I noted the past tense used. It was penetrated.
    – Valorum
    Mar 1, 2017 at 9:39
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According to the Wookieepedia article on Shields,

Some shields were one-way shields that only allowed a person to come in through the shield, but prevented passage back out through the shield

Also, the majority of ships in Star Wars have shields which are up in combat, but they obviously fire through them to attack enemies.

It makes sense for the Death Star II to have shields which were only one way, so they could be both defensive and offensive at the same time, while the shield over Scarif would make sense to be both ways, as they would want to control the flow of ships and lasers both in and out (no unauthorized entries or exits).

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    Droidekas' shields aren't one way. See this: scifi.stackexchange.com/a/113012/931
    – Ragnarok
    Feb 27, 2017 at 16:46
  • @user931: It is not unreasonable for there to be a variety of different shield designs, each with pros and cons. Utility, functionality, requirements, power consumption, etc, etc, could all factor into a particular shield's design and resulting abilities.
    – Ellesedil
    Feb 27, 2017 at 20:48
  • I understand most ships have shields active in combat, but I can easily accept those being of a different kind: they're projected by the ships themselves, do not prevent physical contact etc. The Scarif and Death Star shields seemed too similar, that's what made me ask the question (after I've finally watched Rogue One).
    – Angew is no longer proud of SO
    Feb 28, 2017 at 7:19
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There are a few references in Legends to the idea that very large-scale shields (like planetary shields) operate in "sectors" or "zones" that can be selectively turned off or overloaded. For instance, during the Yuuzhan Vong invasion of Coruscant, several shield sectors on the far side of the planet from the Vong fleet are lowered so refugee ships can escape; later on the shields are noted as failing in sections under heavy bombardment. (This is similar to the idea of "double front" shields and the like seen in the movies, but more granular.)

It seems plausible that just part of the Death Star's shield could be lowered during the firing sequence to let the beam out, then raised afterwards. A ship would have to be extremely lucky to pass through the shield in that brief moment without being vaporized by the beam, so for all practical purposes the shield is still up.

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