Explosions In Space
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Basic Information

This Speculative Fiction Trope is about how Sci-Fi films and movies pretty much always do explosions wrong, especially explosions in outer space.

What You See

In a movie, an explosion in space will look pretty much just the same as an explosion here on earth - or, at least, the hollywood version of an explosion here on earth. For most audiences this is an Acceptable Break From Reality, or possibly not even noticed.

In otherwords, explosions in space are big fireballs or pillars of flame. Glowing debris and a Planar Shockwave are optional, but likely. It's almost mandatory to combine them with sound effects so massive your seat vibrates. And most everyone is just fine with that, because of the Rule of Cool.

Is Not What You Get

In reality, however, explosions in outer space are nothing like that.

For one thing, you can't hear the explosion, cause there's no air to carry the sound.

That also means there's definitely no Planar Shockwave or Mushroom Cloud, as a similar effect only happens on earth because of interactions between the explosive, the atmosphere, the plane of the ground, and gravity. Several of those four factors are missing in space, even if your explosion is happening on a large pressurized ship with artificial gravity. You still have no atmospheric resistance outside the vessel, because space is a vacuum.

As a result, the correct shape of an explosion in space is nearly spherical. Force is applied evenly in all directions, sending debris nearly evenly in nearly every direction. There's also no air resistance to impede the movement of debris, so the explosion should expand almost too quickly for the human eye to process. There's no oxygen to sustain the fire and reactions. There's also a great big void for the heat to radiate out into, as opposed to atmosphere that would retain heat in a terrestrial explosion. The result would be a rapid burnout of the fireball. The big glowing sphere appears and vanishes in microseconds, leaving behind an ever-expanding spherical halo of debris.

Again, there's no atmospheric resistance to slow it, so the debris will just keep going at the same speed until it impacts something or gets caught in a gravity well. Luckily, space is big and empty, and there's really no need for ships to travel anywhere near each other. If not for that fact, one explosion could wipe out a whole armada. Unless the Admiral is an idiot (or your space travel rules unrealistic), the space fleet will be barely within (or possibly beyond) visual contact of one another. At that range, the debris is going to be so spread out it will probably miss you. Keep your fingers crossed.

For more information, see:

  • Inverse-Square Law to learn about the density of projectile debris over distance, and the force of the explosion over distance.
    • Bonus Fun-Fact: As mentioned above, projectiles in the vacuum of space have no air resistance and thus do not decelerate over time. The particles still spread out as mentioned on the Inverse Square-Law page, but if even one little speck hits something hours later it can do a lot of damage. Especially if you consider the extra velocity that might be conveyed from the speed the ship was traveling at before it exploded. If it's a Faster Than Light star drive a little scrap of wreckage could be a world-destroyer.
  • Blast Injuries to learn about the types of wounds that explosions can cause.
    • Bonus Fun-Fact: If an explosion happens inside a ship, and the shockwave isn't strong enough to rip that ship apart (or at least break a hole and vent the atmosphere), the shockwave will ricochet about inside the ship. So Blast Injuries of the Primary and Tertiary categories may be multiplied inside the ship.
  • Space Exposure for the effects if an explosion flings you out of your ship, or reduces your ship to wreckage.
  • In Space No One Can Hear You Roll The Dice to learn more about how sound works (or rather, doesn't) in space.



Game and Story Use

  • Familiar Hollywood style explosions are, well, familiar, and thus easy for the players to visualize.
  • Realistic space explosions are trippier, and possibly creepier, because they don't match our expectations and imaginings. Describing them accurately will make your game memorable, and can establish the "otherworldness" of outer space.
    • If the PCs are supposed to be scientists or veteran astronauts, you'll need to take care to explain that this is what space explosions are supposed to look like. You don't want the PCs assuming there's some clue hidden in the oddity of the explosions, and going chasing after a red herring that their characters should have known was perfectly normal.
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