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In the semi-realistic space combat I design, the following rock-paper-scissors relation holds:

  • lasers beat rockets
  • rockets beat armor
  • armor beats lasers

The level of technology is not too futuristic: no antimatter, no space elevators, no teleportation. Distances are long enough to make direct usage of lasers problematic due to the light scattering and diffraction, but short enough to use rockets with explosive payloads.

Unguided weapons

All is merry and well here until unguided weaponry arrives. Bullet-like things are not ruining anything as they are either too slow or too fast.

Too slow is self-explanatory. A spaceship is likely to perform defensive maneuvers by firing engines at random, so nothing can predict where it would be in time the bullet is supposed to hit it.

Too fast makes a bullet glow with heat. It heats by hitting trace molecules of gas in space. After all, it is not that empty. A bullet is destined to evaporate or to be picked off by a point defense system.

The ones that are ruining space combat are unguided bombs and mines. Slow-moving nukes that will blow up or melt everything too close to them. You can't avoid mines, because they are invisible. The absence of significant heat signatures makes them impossible to detect.

The question

How feasible it is to use nukes as a spotting mechanism? Blow one in front of you, being at a safe distance, of course, for it to heat everything around it, opening a window to detect otherwise invisible objects.

Something like a flash is used in cameras or a powerful radar impulse.


P.S. Let's pretend for a while that it is possible to mine in such a clever way that there are reasonable chances that a mine will find its target if unnoticed.


EDIT: Maybe the nuke might be not a conventional one, but rather some variation of enhanced radiation weapon, but with focus on alpha particles for increased absorption and thus heating.

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  • $\begingroup$ Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Worldbuilding Meta, or in Worldbuilding Chat. Comments continuing discussion may be removed. $\endgroup$
    – L.Dutch
    Jul 30, 2023 at 18:04

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Possible, with extenuating circumstances

As others have pointed out, using nukes like flashbulbs is very inefficient compared some systems like radar, lasers, or particle beams. Unless the objects you're hunting for are unreasonably good at stealth, it should do the job pretty well, and setting off expensive nukes is wasteful.

If otherwise, you're likely not searching for thermal signatures of slightly hotter rounds. A nuclear pulse would illuminate everything in high energy light which can't really be stealthed against for small objects like bullets. Sensors could be physically shuttered during detonation then snap open and search the sky for scintillations of x-ray or gamma ray light. Bullets are likely to be made of dense metals which partially scatter the light.

Exploding a nuke would also reveal the positions of your own in-flight munitions to the enemy.

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Unfeasible if you want to be realistic

I am assuming you are dealing with vast distances, because:

Too fast makes a bullet glow with heat. It heats by hitting trace molecules of gas in space. After all, it is not that empty.

All five probes we have sent out the solar system are moving relative to us at bat-out-of-hell speeds. They have crossed dozens of AU's and are still mostly intact and cool. For heating to happen as you describe, in space, requires sci-fi speeds and specially greater distances.

If that is the case, then mines are going to be spread really far apart. Even if you were blowing up Tsar Bombas (the strongest nukes ever built, with potential yields of 200 megatons a piece) the way energy propagates in space means relatively faraway objects wouldn't get much radiation.

Remember, the Sun radiates much more energy in one second than every bomb we ever have exploded combined. Yet our probes fly safely through the solar system. And even with all that radiation illuminating everything around the Sun, we still usually detect asteroids that pass close to Earth AFTER they've passed the closest approach mark.


You can of course ignore all this and just have fun. One of my favorite videogames is FTL, which has a similar rock paper scissor system (shield beats laser, which beats rockets, which beats shields). The physics in that game are closer to Looney Tunes than they are to reality, yet it is fun, addictive and went on to score several important awards in the industry.

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    $\begingroup$ The neat part is that if you hunt for nukes and they are too far to be heated up, it means that you are relatively safe! FTL is a great game btw:) $\endgroup$
    – FrogOfJuly
    Jul 28, 2023 at 10:08
  • $\begingroup$ "more energy in one second than every bomb we have ever exploded combined" - that's not quite the flex you think it is. One second is a long time when we're talking nukes. A big fusion bomb might greatly exceed the Sun's power output for a tiny fraction of a second. Whether that flash would be enough to see anything is a different story. (And I think the main mechanism by which it might work would be reflected X-rays, not by making the target glow with heat.) $\endgroup$
    – causative
    Jul 30, 2023 at 7:03
  • $\begingroup$ Well, on closer inspection to "greatly exceed" the Sun's power output is a tall order, but a really big fusion bomb could match it. Based on nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html the fusion part of the explosion could take 20 nanoseconds to go off. The sun outputs 4*10^26 W. A fusion bomb with an output of 2 GT TNT (released over 20 nanoseconds) would be sufficient to match that. Necessary size of the bomb might be reduced if it could be designed to release the X-rays over a shorter time period than 20 ns. $\endgroup$
    – causative
    Jul 30, 2023 at 7:18
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    $\begingroup$ If it worked it would only give you an instantaneous snapshot. You'd probably want to do a second flash right after so you could get the speed of the things you saw. $\endgroup$
    – causative
    Jul 30, 2023 at 7:43
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You Probably Could, But It's Really Inefficient

So the actual heat emitted by a nuclear bomb is comparatively minor. The enormous thermal effect from a nuclear weapon in atmosphere is a result of compressive (blast wave) heating and x-ray heating of the bomb components and surrounding air (which you don't have).

So you'd be looking at how much heating could be induced by the radiation emitted by a nuclear explosion, and that drops off as the square of the surface area away from the bomb, and space, famously, is big.

So you could detonate clouds of nukes at a distance barely sufficient that they wouldn't make your hull glow like a lightbulb, and they'd probably heat up otherwise-invisible objects within their effective radius by some measurable amount, but devices intended to be invisible in space are already going to be very adept at shedding heat, since solar radiation is going to be enormously greater than the energy delivered by a nuclear bomb at any reasonable distance.

You're much better off sweeping likely locations with lasers.

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  • $\begingroup$ I think the main problem with the sun is that if you are an attack fleet, then you are going toward the sun and you can't reliably see the heated side of the objects. $\endgroup$
    – FrogOfJuly
    Jul 28, 2023 at 10:19
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    $\begingroup$ "You're much better off sweeping likely locations with lasers.": especially since it's quite commonplace to build lasers capable of extremely brief pulses, giving them peak powers millions or billions (or more) times higher than their average power requirements. The best laser-absorbant stealth mine coating will produce a flash of plasma with each pulse from a decent laser at ranges where a nuke would do nothing. $\endgroup$ Jul 28, 2023 at 13:13
  • $\begingroup$ @FrogOfJuly Only if everything you're attacking is in the small segment of the system between you and the star, and you're attacking from just one direction with no reconnaissance drones. $\endgroup$ Jul 28, 2023 at 13:14
  • $\begingroup$ @ChristopherJamesHuff, the problem with lazers is that you need to know where to search. The whole point of mines that you do not have this knowledge $\endgroup$
    – FrogOfJuly
    Jul 28, 2023 at 13:36
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    $\begingroup$ @FrogOfJuly - you absolutely do know where to search: everywhere within mine-reach of where you're about to go. $\endgroup$
    – jdunlop
    Jul 28, 2023 at 17:31
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Let's ignore the other answers, I like the idea!

And I'm taking your qualifier "semi-realistic" at face value. Frankly, I think science fiction without generous flexibility is boring beyond belief. If I wanted realistic I'd take astronomy and astrophysics classes.

The reason I like the idea is that without invoking some form of FTL communication or travel, no information can travel faster than the speed of light. What better way, then, to spot the enemy than by using light!

I also like the the underlying proposition that guidance is a problem. I can believe that. No matter how fast the computers, all an attacker needs is to attack at a greater distance and speed and the computers can't easily keep up. Especially if it's difficult to track the attacker in the first place.

So let's put some big ol' honking nukes on the top of the fastest rockets you have and send about twenty or so of them out either in a sphere ('cause we really don't know where anybody is) or a more restricted arc (because they were stupid and put some party fizz in their engine exhaust and for just a moment it looked like New Year's Eve out there). We need a practical distance because we really want, ideally, for the nukes to get behind the attacker(s). But it's also not useful to send them further than the outer limit of our own ability to defend. That's a complicated scenario that has to do with burn limits, velocity, distance between nukes, and a bunch of other things. But let's assume this isn't unreasonable.

Then, dramatically, using several million dollars worth of Hollywood's best special effects, we blow the nukes. Simultaneously.

The result is a spectrum of electromagnetic emissions. Where your computers excel is reading, collating, analyzing, and reducing the data.

Yeah, but has this been done before?

In a sense, yes. In the Star Trek TNG episode "Redemption," Commander Data uses photon torpedoes to reveal cloaked Romulan ships. But this isn't a bad thing — frankly, it means your premise has already been considered by SciFi writers and determined to be fundamentally sound.

Aha! So we've established my proposal is sound in principle, now we're just haggling over price. Captain Jack Sparrow

I'm not going to comment extensively on the "realism" of the solution. Of the many reasons we use radar and not randomly tossed bombs (call it "flak") one is that radar is useful so long as there is energy to operate the emitter/receiver/analysis circuits and the nukes are only useful as long as you have nukes. A bigger ship to carry more nukes is usually not the choice of preference.

But I personally think "real" is overrated. Really overrated. I'm having fun re-reading Isaac Asimov's Prelude to Foundation and believe you me, despite a whole lot of award-winning imagination, there's really very little "realism" in the book. Especially when it came to costumes.

Because you go in the jungle, I can't see you. You know, it's like wearing stripes and plaid. For me, I want to do something different. You know, you go in the jungle, make a statement. If you're going to fight, clash. You know what I mean? Good Morning Vietnam

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The ICBM strategy has some useful lessons here.

The ICBM in its silo or submarine is a long way from the enemy. The enemy may not know where it is, exactly. It can be launched long before an attack is threatened.

The ICBM is its boost phase is perhaps it at its most vulnerable. It has dresses from travelling through the atmosphere. It has lots of fuel that could cause it to explode. A rifle bullet could down one if it got in the wrong place. But the boost phase only lasts a minute or so.

The ballistic phase comes next. The warhead is travelling ballistically for most of its journey. It can be spotted by radar but it is a pretty small target, and it may be surrounded by decoys with similar speeds and cross-section. If it is shiny on the outside, you can't use a laser on it. Even if you could heat the mirror, most metals form a plasma that will insulate the target against further radiation. You are going to have to smack it with something physical, like a bullet.

There is a small window as you approach the target. In airburst nuke might irradiate the incoming nuke, causing it to have more neutrons than it would on average, which would mean the chain reaction might happen ahead of the designed minimum volume. This was seen as a possible failure mode for multi-ICBM attacks. I think an intelligent nuke could compensate for this. I wonder whether you could have coherent neutron emission as a beam weapon. That would provide a much higher neutron dose which could do damage.

The re-entry stage only lasts for a few tens of seconds. At this point, you know where the nuke is as any light decoys would have burnt up. But an efficient incoming warhead ought to target itself as accurately as possible, and this manoeuvrability means it could also dart around a bit. And it will probably detonate in the air.

An attack in space will probably follow the lines of an ICBM attack. Sabotage is best. Get it while it is launching if you can. In the ballistic phase it is really hard to get, and the target may hidden among many decoys. In the last moments, there are a set of desperate things you might try, including detonating your own nukes. Lasers and armour hardly figure.

There is one other option in space. If you are in space yourself, move out of the path of the incoming objects. They will either have to change their trajectory early, which gives them away (unless the decoys can do this too), or they have to alter course suddenly and violently at the last possible moment, which takes fuel and a lot of forethought.

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  • $\begingroup$ I like that you are comparing space combat with an ICBM attack. I have never thought of it that way! The neutrons as a way to poison the warheads is also a fantastic idea $\endgroup$
    – FrogOfJuly
    Jul 29, 2023 at 18:36
  • $\begingroup$ A concentrated isotope is in effect a population inversion. You could make a NASER for your neutron beam. I doubt if anyone has ever tried it. It is a bit tricky because there is no neutron mirror, so you get two beams in opposite directions. Don't stand behind it when you push the button. $\endgroup$ Jul 29, 2023 at 18:58
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There are so many things wrong that honestly, I don't know what's worse. First of all, some basic constraints:

  1. Refraction occurs when light passes from one medium to another. In an atmosphere, there are many density changes and suspended particles that cause this effect and result in energy loss as light travels through the medium. In the vacuum of space, none of this happens, and with properly calibrated lenses, it is entirely possible to go from a low orbit (40,000 km) to an outer orbit (120,000 km to 260,000 km) without any significant problems or noticeable separation issues.

  2. Battles would always have to obey orbital mechanics, meaning that there would be easily predictable routes. Leaving a planet's gravity well consumes a lot of propellant, and maneuvering outside the gravity well of something else is much more difficult. Unless your space battles take place in interstellar vacuum, everything would be in some kind of orbit, whether it's a planet, moon, or star.

  3. There are no "slow" bullets in space. Orbital mechanics dictate that anything in orbit is moving at orbital speed. Newtonian mechanics tell us that velocities add or subtract depending on direction. So, the slowest impact you could have would still be at orbital speed, which is incredibly high. Even a piece of paint would become an anti-material projectile at those speeds. Additionally, bullets fired from one orbit to another would have a vector of velocity, ultimately resulting in a much more destructive impact. If the collision is head-on, you'd have a bullet traveling at orbital speed + the muzzle velocity + the velocity of the impacted ship.

  4. There is no medium in a vacuum, so there is no friction. Therefore, "fast" bullets are not much hotter than "slow" ones. Neither would glow unless they have a tracer, and both would be easily visible with an infrared system when against the sun and completely invisible in direct sunlight.

In response to your question, the answer is No, definitely not done like that. Radars exist, and if your mines/nuclear bombs have enough metal, they'll be detectable. Additionally, even a loose screw in orbit could act as a mine itself since any collision is at least at orbital speed. Your minefields would be much less efficient than just throwing a bag of rivets into space and letting them spread throughout the orbit. Another issue with your idea is that there is no medium in space, so a nuclear bomb is quite useless. The gigantic plasma balls akin to a raging star that one imagines with nuclear weapons only occur in an atmosphere because it has air that can be turned into plasma, which expands, causing a shockwave followed by heat transmitted by convection. These processes cannot occur in space since both convection and conduction require a medium, and radiation is inefficient. Your nuclear bombs wouldn't efficiently explode in space; they would vaporize instantly along with anything within 100 or 200 meters. Anything farther than that would be safe. The worst part is that you achieved the opposite of what you wanted; the electromagnetic storm from a nuclear weapon would blind radars, while light and infrared radiation would blind all your sensors.

In summary, no, your idea is not remotely possible for countless reasons.

Thanks to jdunlop for pointing out a typo: it is refraction not diffraction.

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    $\begingroup$ It's a bit hard to take your answer enumerating the things wrong with the OP seriously when you also get something badly wrong right off the bat - when light passes from one medium to another, it undergoes refraction. Diffraction is very different. $\endgroup$
    – jdunlop
    Jul 27, 2023 at 21:58
  • $\begingroup$ @jdunlop Thanks for the correction, it was a typo. $\endgroup$ Jul 27, 2023 at 22:38
  • $\begingroup$ not sure why this is down-voted. Nuclear-bombs-as-propulsion is a viable design, and the OP has a lot of problems in their assumptions. At orbital speeds, opening a window and throwing a bag of cat litter into the path of the enemy would be devastating. $\endgroup$
    – Yorik
    Jul 28, 2023 at 17:48
  • $\begingroup$ I think that your answer is a valid criticism in the case of hard science setting, but what I am designing, sadly, can't be that realistic $\endgroup$
    – FrogOfJuly
    Jul 29, 2023 at 18:42
  • $\begingroup$ This answer now starts out arguing against something that isn't even in the question. It is diffraction that ultimately limits your ability to focus a laser across a long distance. The question doesn't even mention refraction. $\endgroup$ Jul 30, 2023 at 17:47

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