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What would happen if I throw a grenade in space? Would it explode? Or will it just keep floating forever?

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  • $\begingroup$ Whereever would you throw it otherwise? $\endgroup$ – LocalFluff Jun 29 '14 at 17:52
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    $\begingroup$ In space, nobody can hear you yell "Fire in the hole!" $\endgroup$ – Mason Wheeler Jun 15 '15 at 16:00
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Yes, it would explode. Most hand grenades are nowadays triggered chemically, electrically or contain a fuze enclosed within the assembly, so they don't require atmospheric oxygen to ignite, are watertight and otherwise more reliably go off at a preset time since activation.

You would however create a large number of dangerous debris that would float forever, if exploded in higher orbits or deep space, or at least until they impact something, i.e. transfer their momentum onto another body. In lower orbits, the smaller the fragments, the lesser their kinetic potential and would eventually decay their orbit due to still some atmospheric pressure and thus atmospheric drag slowing them down. Depending on the materials these fragments are made of, and their surface area, they might evaporate on reentry, further disintegrate due to surface ablation into smaller fragments, or make it to ground at these fragments' terminal velocity more or less intact.

Do note though that if you're in Earth's orbit, you're orbiting it at many times the speed of firearm projectiles (roughly 7.7 km/s in LEO while firearm bullets usually achieve a bit over the speed of sound at sea level or even less, see e.g. this page for comparison), so while hand grenade fragments would travel away in all directions from the point of explosion, they would retain more-or-less same orbit you're in. They might boomerang (can it be used as a verb?) and hit you many orbits around the Earth later at same relative velocity they were at first moving away from you. Not recommended!

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    $\begingroup$ "Don't try this on your first EVA, kids." $\endgroup$ – ChrisR Jun 28 '14 at 8:37
  • $\begingroup$ The key factor in space debris lifetime isn't object size, it's ballistic coefficient - the ratio of mass to surface area. Otherwise, nice answer! $\endgroup$ – ThePlanMan Jun 28 '14 at 14:27
  • $\begingroup$ @FraserOfSmeg The ratio of mass to surface area is directly proportional to the size of these fragments, if they're made of homogeneous materials (which I'd expect on a grenade, that are usually made to fragment, to be the case). $\endgroup$ – TildalWave Jun 29 '14 at 14:51
  • $\begingroup$ +1 for pointing out how projectiles in space keep going until they ruin someone's day. $\endgroup$ – Mason Wheeler Jun 15 '15 at 16:02
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It depends on how long the grenade has been exposed to space. You might find the vacuum got to the mechanism if it's been out there long enough. Assuming the trigger doesn't fail due to vacuum welding it's going to go boom.

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    $\begingroup$ Neah cold welding shouldn't be a problem on weapons. They're either well oiled / lubricated or they fast become useless also in the atmosphere. One of the first items you learn to use in military is gun oil canister and wipes. About two weeks before they let you handle a shotgun. :) $\endgroup$ – TildalWave Jun 29 '14 at 15:08
  • $\begingroup$ @TildalWave Oil on guns, sure, but oil on grenades?? And how long does oil last in space, anyway? $\endgroup$ – Loren Pechtel Jun 29 '14 at 20:11
  • $\begingroup$ No idea how long it would last, but yes, anything metallic that moves and is exposed to the environment should be oiled / lubricated, that includes the spring mechanism on some older hand grenade designs. Safety pin(s) might not be oiled though, but they're all assembled in atmospheric conditions so unless there's a lot of wear like scratches (not something I'd expect on grenades), top layers would be either oxidized or anodized, so again no possibility of cold welding. Bigger problem would IMO be thermal cycling. But I somehow doubt OP had that in mind with the question. $\endgroup$ – TildalWave Jun 29 '14 at 21:16
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    $\begingroup$ @TildalWave True. The basic answer is that it is even more dangerous in space as the shrapnel won't slow down. I'm just not sure you won't get a hangfire. $\endgroup$ – Loren Pechtel Jun 29 '14 at 21:46

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