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In many sci-fi works, spaceships do not trigger a nuclear explosion upon destruction. Presumably this would be because of sophisticated fail-safe measures. However it occurs to me that having a ship explode on destruction would provide a severe deterrent to anyone trying to attack the ship. (Mutually Assured Destruction.) Especially when predicting bloody conflicts such as in war, it would seem the fail safes should be removed.

So what reason is there to not disable these fail safes as a deterrent? Is it an environmental concern because radiation could affect nearby planets?

EDIT: Some answers have addressed the fact that some engine types will not necessarily explode even without fail safes. Some others may not explode violently enough to cause damage in space to anything that isn't very close.

However this question is intended to be more concerned with why fail-safes would be put in place on an engine that is prone to violent explosion, such as an antimatter engine with a sizable antimatter reserve for extended voyages. Assume enough antimatter and short enough combat range that the ship would stand a chance to destroy the attacking ship if it exploded.

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    $\begingroup$ you are literally traveling in a missile $\endgroup$ – user6760 Sep 7 '17 at 1:23
  • $\begingroup$ Space battles are likely to occur with the opponents a great distances from each other. Even a few hundred kilometres is enough to make one safe from a megaton scale explosion eg. By far the closest people to the explosion would be the crew of the ship fleeing in the escape pods. $\endgroup$ – smatterer Sep 7 '17 at 2:12
  • $\begingroup$ @smatterer Yes but I'm considering a space ship detonating could be way over megatons, especially if it ran on antimatter and had a sizable antimatter reserve. $\endgroup$ – Braydon Sep 7 '17 at 23:00
  • $\begingroup$ Fair enough. It would depend on how big the explosion was. As a back-of-the-envelope example, 100kg of matter converted to energy would be 9EJ. At a distance of 1000km there would be about 2.8MJ/m^2 . That’s roughly the amount of solar energy that an Earth satellite receives in 35 minutes. Any escape pods would still be the closest people to the blast unless the disabled ship was left as a booby trap. $\endgroup$ – smatterer Sep 8 '17 at 10:53
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This could be entirely different based on the technology base of each scifi universe. Despite popular belief, nuclear reactors can vary in meaning and design, and may not even explode at all. A traditional fission reactor for example would more likely have a meltdown (melting of internal components) before it could get to a point of catastrophic explosion; which would result in a loss of all power, essentially ending the battle. The currently experimental fusion reactors however, while still nuclear, are a completely different process and reaction; and wouldn't really explode much different from the explosion of an MRI machine if you want to look up a video for comparison. It makes sense to assume that an advanced space-fairing race would have the technology of a fusion reactor that doesn't require the same kind of fail safes.

So the simple answer may simply be that there is no reason to disable fail safes that don't exist. If there is no risk of an explosion of the kind you are expecting, why would you need a fail safe for it?

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  • $\begingroup$ Yes I suppose that could be. Still I'm more interested in why they would deliberately stop the ship from exploding on destruction. I'll change the question to concern antimatter based spaceships, that would certainly explode on a phenomenal level. $\endgroup$ – Braydon Sep 7 '17 at 22:59
  • $\begingroup$ After your update it looks like you are just really trying to find someone to legitimize your pre-existing idea. Not that your idea is invalid at all, but put in different words you are essential describing some sort of self-destruct protocol. In that case, the protocol itself would be to remove any fails safes, or to ignite the reactor yourself. At this point its a matter of terminology, not plausibility. Even if you use a reactor that doesn't accidentally explode in spectacular fashion, an intentional self destruct could easily be used to the same effect. $\endgroup$ – TitaniumTurtle Sep 8 '17 at 17:31
  • $\begingroup$ Well I was more looking for something satisfactory to contradict my preexisting notions. Still doesn't seem that is happening so I guess I'll just accept the answer that comes closest. $\endgroup$ – Braydon Sep 8 '17 at 19:26
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Pointless, improbable, and not a concern

It is a deterrent? Not really, no, because you can expect space battles to happen at such long range that the enemy will not be caught in any such explosion. A mere kilometer/mile or so away from a nuclear explosion in space, a ship will be relatively safe. This is because the main effect of a nuclear explosion is the shock wave. Since there is no atmosphere in space to propagate the shock wave, a nuclear explosion in space is not nearly as violent as one on the surface of Earth. Instead the main effect will be heat heat pulse and the radiation pulse. Both of these diminish quickly by the square of the distance to the explosion.

It is also not technically credible. Fission reactors cannot be brought to explode in any kind of spectacular fashion. During the Chernobyl accident — which by any and all accounts must be considered a worst-of-the-worst scenario — people in the control room were not aware the reactor had ruptured in two separate explosions for several hours. Fusion reactors would be even less likely to explode since they will be dependent on a steady flow of fusionable fuel into the reactor to even keep going. Anti-matter reactors? Well... there we could get a sizable explosion going. But if so then there must already be anti-matter weapons. If a dying ship is to give one last "Good Game, and F*CK YOU!" salute, then I would rather expect the ship to send out all its missiles/kill drones for that, especially since the risk of Friendly Fire is significant with the ship blowing up.

Further more, in case the ship needs to be destroyed then that must be a controlled and deliberate action, or through a dedicated mechanism that guarantees the proper execution. Otherwise you cannot be sure of when it happens nor how effective it is. If you have made the decision that the ship will be scuttled, then you need to know this will actually happen, and you will not be left with a fizzle that leaves most of the ship intact.

As for the environmental concerns: no... that is a complete non-issue. A star bombards its planets with so much radiation that a nuclear bomb in space is like tipping over one of those water bottles...

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(Image Source)

That said...

Obviously the self-destruct trope — both deliberate and inadvertent — still manages to make its way into fiction all the time. Usually though it is for any of the following:

  • Prevent capture and with that a fate worse than death
  • Prevent valuable resources from falling into enemy hands (such as secrets, technology and crew members)
  • For glory! ...or at least to spare us from having to live through the shame of defeat.
  • We ram them and take them with us. There is a subtle difference here in that this is a deliberate and controlled action whereas what you propose is happens when the defeated have lost all control.
  • Convenient tension generator that adds excitement to the narrative

But mutual destruction in your average space battle very rarely seems to do it.

Summary

So to answer your question: is there any narrative value in the idea of having the protagonists pull out their reactor fail-safes in the event of a space battle? No, it does not make any kind of sense. It is too uncertain, too uncontrolled, not technically plausible, and most likely pointless.

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  • $\begingroup$ Preventing technology or sensitive data from falling into enemy hands is also a commonly cited reason in sci-fi for self-destructs (and, in fairness, also to some extent in the real world). $\endgroup$ – user Sep 7 '17 at 11:14
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    $\begingroup$ As for the destruction to be controlled and thorough, Spaceballs does one take on this where the self-destruct mechanism destroys most of a spacecraft but leaves a few large chunks essentially intact. Not what you want to happen. $\endgroup$ – user Sep 7 '17 at 11:15
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    $\begingroup$ "technology or sensitive data"... that is so say: "valuable resources". :) $\endgroup$ – MichaelK Sep 7 '17 at 11:36
  • $\begingroup$ Indeed valuable resources, indicating that prisoners might not be even the most valuable resource. $\endgroup$ – user Sep 7 '17 at 11:51
  • $\begingroup$ Consider David Weber's Honor Harrington universe. Ships run on fusion plants, when one takes a direct hit it tends to go boom quite spectacularly. Effect: It's unlikely there are any survivors. $\endgroup$ – Loren Pechtel Sep 8 '17 at 1:04
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So what reason is there to not disable these fail safes as a deterrent?

Two more reasons to add to the many good answers:

  • the ship might be part of a fleet, and exploding it is likely to damage and/or disrupt friendlies much more than enemies, since the former are nearer.

  • the propulsion system might have a really catastrophic failure mode - rending the spacetime continuum and creating a perpetual navigational hazard (this is a plot device in the Lacuna series), or backlashing across the light-years against the Ancient Tree of Spaceways whose seeds power the engines.

Depending on the culture, you might also get a morale hit or efficiency loss in battle, when the crew begins dreading the imminent destruction - perceived as more certain than that meted out by the enemy. Of course in some other cultures you might get the opposite effect.

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@user6760 comment already hint the answer.

Because there are people in it.

These people might survive the destruction, via emergency pod, or even ejecting themselves to space (Warning! Do not try this at home!). Although the survival probability is very slim, it is better than none when your ship explodes spectacularly.

Additionally, the damage dealt by the explosion may be considered minor and such does not worth considering between a possibility of survival and dealing damage to enemy ship. Exception that the damage may be substantial enough to fighters, but usually they are fast and agile enough to escape the (slow) explosion.

Different opinion may arise, though, if the explosion instead send a destructive gravitational wave that pierces shielding and armor, damaging enemy internal system and crews. However, this may backfire if you are in the middle of your fleet and you got sabotaged.

Basically, the ability to control the destruction, maximizing the damage to enemy while minimizing the damage to your fleet, is far more useful than uncontrollable double-edged sword. Except you can release that to the middle of your enemies. Then again, it's better to use missile instead.

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  • $\begingroup$ I think "uncontrollable," from your last paragraph, is the key word here. This is not a precision designed weapon, but rather a messy messy improvised device. Anyone disabling the safeguards would have to be ready to dance around this uncertainty (such as the emergency pods you mention) $\endgroup$ – Cort Ammon Sep 8 '17 at 2:08

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