How would a nuclear explosions operate in the cold, hard vacuum that is Traveller space combat?

Battlestar: Galactica and Mobile Suit Gundam SEED both portrayed nuclear weapons (or fusion/fission technology in general) in an outer-space environment. In one episode of BS:G, the Galactica gets nailed by a thermonuclear warhead that managed to penetrate its curtain of defensive fire, but (to my surprise) the ship survived being crippled or destroyed outright.

I've been digging into MgT-2 over the last few months. Its hard science fiction approach reminds me of The Expanse. The more I dig into it, I find myself daydreaming about the reality of combat in space. No atmosphere to conduct sound, so combat is mostly quiet; ship attack from long distances takes minutes, even longer at extreme ranges. Combat in a hard-sci environment takes on some qualities I'm not used to in most sci-fi settings, and I like it.

How does Traveller handle such considerations? As far as I've managed to peruse, the combat system handles conventional weaponry, but doesn't go into some of the effectively environmental effects of non-conventional occurrences - like the detonation of a fissionable warhead.

In particular, Traveller considers radiation exposure in open space as fairly harmful over short periods of time; without the proper shielding, space travel over long periods of time is extremely hazardous, and space walks without protective layering are reckless. Would the radiation released from a nuclear explosion be more or less considerable in a vacuum?

I appreciate your consideration, and any insightful answers. Direction towards rules, homebrew solutions, and specific examples would be great!

  • \$\begingroup\$ Are you using strictly the original traveller line? Or are GURPS Traveller's ways of handling nukes relevant to you (given that it tends to have well-researched handling of such topics and respects science)? \$\endgroup\$ Jul 10, 2019 at 14:34
  • \$\begingroup\$ @vicky_molokh The question mentions MgT-2 so Mongoose Traveller seems to be the case here. \$\endgroup\$ Jul 10, 2019 at 16:25
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    \$\begingroup\$ I have removed the two world building pieces from your question and voted to reopen. I suggest that you take those two elements of your question to World Building SE. (The original question is in the edit history, just click on "edited {x time ago}" and you'll see all versions. \$\endgroup\$ Jul 10, 2019 at 16:27
  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$
    – V2Blast
    Jul 10, 2019 at 22:30

3 Answers 3


I don’t recall seeing any specific rules for nuclear explosions in space combat in Traveller, but Traveller promotes the “hard space opera” meme, suggesting that in the absense of any canonical statement to the contrary, one should go with a “realistic” response to a situation. I therefore looked into the effects of a nuclear explosion in space, and found a discussion of the effects on NASA’s website. While the radiation level at the point of detonation is no more intense in vacuum than it would be in atmosphere, the dropoff in vacuum is far slower than in atmosphere - that is, if we coin the term “half-distance” to represent the distance from the point of detonation at which the radiation intensity is half of its value at the point of detonation (analogous to “half-life”), the “half-distance” for a detonation in vacuum is far larger than for the same detonation in atmosphere.

However, the following effects that are routinely expected to be encountered in atmospheric detonations are not present in vacuum detonations:

  • Electromagnetic Pulse (EMP) – this is caused by gamma radiation impinging on atmosphere; with no atmosphere in vacuum, there is no EMP
  • Persistent fallout – this is caused by soil and other loose debris being drawn into the explosion by atmospheric motion due to superheating of the atmosphere around the detonation, irradiated, and then “blown out” to settle over the area surrounding and downwind of the detonation. With no atmosphere, there is nothing to draw in material to be distributed; material on which the radiation from the detonation impinges will be irradiated “in place” and not further spread, unless it is caught in the immediate blast from the detonation. In any case, “cleanup” of irradiated material is either easier or may be ignored in space combat.

The High Guard book covers this as far as MGT-2 mechanics go. Spinal mount meson and particle weapons are on pg. 28, nuclear missiles are on pg. 30, and nuclear torpedoes on pg. 32 Meson screens and nuclear dampers (for defense against these weapons) are on pg. 33.

In summary, all of these do some amount of damage (Meson and particle cannons do the most, torpedoes and missiles do much less.) and Radiation (see MGT-2 core pg. 75). Nuclear dampers reduce the damage from warheads by 2D and remove the Radiation if used successfully. Meson screens do the same for meson spinal mounts. Both seem to provide some protection from particle spinal mounts as well, but I haven't done a detailed reading of the rules so take some salt with that. Page 13 of High Guard also has a brief discussion of the effects of radiation.

High Guard notes that use of nuclear missiles near inhabited planets or in orbit is a violation of interstellar law. The description for nuclear torpedoes doesn't include this tidbit, but I think it's reasonable to apply the same logic to them. Neither meson nor particle weapons appear to have this restriction, possibly due to their poor in atmosphere performance as referenced in their descriptions.

  • \$\begingroup\$ Traditionally, in other versions of Traveller, the Imperium were the only folk (as in the Imperial Navy, Army, Marines and maybe Close Oribt and Aerospace Control forces) who legally had nuclear weapons. Players anywhere other than an active service game would never be expected to have such weapons. That said, if you happen to be outside a hull when a nuke goes off nearby (or is a contact hit), then one would think that would be almost instantly fatal for an individual caught in the blast. And as another answer states, radiation has greater reach than inside of an atmosphere. \$\endgroup\$ Feb 4, 2021 at 4:45

I recall there being a table in Striker (or for Striker in a Challenge or Journal of The Travellers' Aid Society magazine) which laid out some effects from nuclear weapons. I am uncertain at this time if that included modifications for vacuum worlds. That may be another resource despite it applying to a prior version of the game.

  • \$\begingroup\$ You recall correctly. Striker Book 2 Advanced Rules includes Rule 39: Nuclear Rounds, with standard nuclear rounds ranging from 0.1 to 100 kton. It also includes Rule 53: Planetary Environment, which includes vacuum worlds, but neither Rule 39 nor Rule 53 references the other or its topic. \$\endgroup\$ Apr 26, 2020 at 12:45

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