A Reddit thread about the early availability and weak damage of nuclear missiles in Stellaris sparked a wider discussion that moved from game balance into the physics of nuclear detonations in vacuum. One player raised this issue framing it as a lore inconsistency rather than a mechanics complaint, and the conversation quickly broadened into arguments about how a nuclear blast behaves without an atmosphere.

The central contention was that, on Earth, much of a bomb’s destructive power is mediated by air: heating the atmosphere produces a shockwave that wrecks structures kilometers from the epicenter. Remove the atmosphere, the critics argued, and that shockwave disappears.

Nuclear weapons primarily deal damage through the shockwave generated by the explosion. A wave needs an atmosphere to propagate. In space, there is no air, and therefore no wave. So in space, a nuclear charge is just a big bomb that heats metal.

In place of an atmospheric shockwave, a warhead detonated in vacuum deposits energy into channels such as:

  • X-ray radiation
  • neutron flux
  • superheated plasma
  • flying fragments of the bomb's casing itself

Not everyone accepted that this reduces the weapon’s effectiveness. Some commenters argued that, absent an atmosphere to absorb energy, a ship would receive more of the bomb’s output because nothing bleeds it off into the air. The counter to that view emphasized geometry: radiation and fragments still expand spherically, so unless the detonation is extremely close or a direct hit, the target intercepts only a small portion of the total energy. The rebuttal gained noticeable support in the thread:

Energy transfer doesn't work that way. The absence of an atmosphere doesn’t mean that the energy which would have gone into the air is somehow redirected into the ship. In a vacuum, X-rays, neutrons, and fragments still spread in all directions, and unless the hit is direct and very close, the ship intercepts only a fraction of the expanding sphere. The atmosphere doesn’t just hinder propagation; it is the medium that converts a significant portion of a bomb’s energy into a shockwave. Remove the air, and you remove this entire damage mechanism.

Participants introduced numerical estimates to illustrate the point. One calculation cited in the discussion claimed roughly 80 percent of the energy in a vacuum goes into radiation, with the balance carried by extremely hot plasma. Using a 100‑kiloton charge detonated at a distance of one kilometer, that estimate suggested a one‑inch armored plate that absorbed the radiation and plasma completely would heat by about 350 °C. In practice, surface ablation, internal spallation, and warping would make the effect harsher on the outer layers, but not sufficient to vaporize the hull; the inverse square law and detonation distance dominate the outcome.

Direct hits were treated as a separate case: a point‑blank strike can be catastrophic. Players noted that in Terra Invicta, a nuclear warhead at point‑blank range will reliably kill even the toughest ships, while a near miss tends to strip outer armor only. It was also observed that in many space‑combat settings a distance of a hundred kilometers is considered “knife‑fight” range.

The thread also debated whether early‑tier missiles in the game could plausibly carry “tactical” warheads. Those weapons were compared to historical bombs dropped on Japan, typically up to about 50 kilotons. The distinction offered was one of intent rather than physics: tactical warheads target specific military assets, while strategic warheads are intended to raze cities.

A technical explanation for the modest damage figures was proposed: nuclear charges can be made directional, focusing energy into a cone aimed at the target rather than radiating isotropically. Real‑world work on such concepts includes the Casaba‑Howitzer, which traces to research connected with Reagan’s Strategic Defense Initiative; fictionally, the Halo universe depicts ship‑based nuclear devices delivering directed energy bursts. The same idea underlies nuclear‑pumped lasers. Thread participants warned, however, that directional designs trade overall yield for focus, which could justify lower damage numbers in a game’s UI.

Defensive abstractions in Stellaris were also discussed. Empires are portrayed as keeping fleets in systems with pulsars that emit powerful ionizing bursts each second, so hulls are implicitly radiation‑hardened. Game terms such as shields, armor, and hit points serve as abstractions for a ship’s survivability rather than literal, physics‑complete defenses. Relatedly, the reality of faster‑than‑light travel was brought up: a vessel moving at FTL speeds would continuously encounter and have to withstand particle flux on its hull, favoring designs with large durability margins. Early in a civilization’s space age, hulls may be powered by fission reactors, and centuries of refinement could plausibly raise survivability before widespread space combat.

Some players argued against trying to fit strict physics to a tech progression: in the game lore, antimatter rockets occupy the third out of five tiers of propulsion, yet a single such detonation is credited with destroying the Vultaum Precursors’ homeworld in backstory. The tech ladder, they said, reflects presumed destructive power rather than explicit energy accounting.

A reply focused on scale; planetary or precursor‑scale weapons can carry far more antimatter than a ship‑launched missile. To illustrate the energy involved in antimatter annihilation, the thread noted that destroying one gram of antimatter releases about 180 terajoules, roughly 40 kilotons TNT equivalent—about twice the yield of the Nagasaki bomb. By contrast, a typical ship missile warhead would likely consist mostly of magnetic field generators and not anywhere near grams of antimatter.

The discussion closed without a definitive resolution. As participants observed, space is vast and the exact balance of effects — geometry, radiation, plasma, fragments, engineering tradeoffs, and lore choices — makes predicting how future space battles would play out impossible to settle in a single forum thread.