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==Explanation==
 
==Explanation==
This comic pokes fun at the properties of {{w|plutonium}}, claiming that it is so unrealistically powerful that it may as well be random science fiction jargon. Indeed, the ability for a metal to radiate energy sounds impossible (this comic leaves out the inherent dangers of highly radioactive material). This is reflected by Megan and Hairy treating Cueball's idea as a joke.
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{{incomplete|Created by a Power Orb. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
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This comic pokes fun at the properties of {{w|plutonium}}, claiming that it is so unrealistically powerful that it may as well be random sci-fi jargon. Indeed, the ability for a metal to radiate free energy sounds impossible (this comic is likely a simplification). This is reflected by Megan and Hairy treating Cueball's idea as a joke.
  
There are devices that need substantial electrical power over long time – on the order of decades – but local sources of energy are insufficient or unavailable, yet constructing a power line or resupplying them with some power source (like fuel, fresh chemical batteries etc.) is either impossible or overly costly. Such devices include maritime beacons and buoys, automatic weather and science stations located in remote areas, and – most importantly – deep space probes and some planetary probes or science packs. Probes sent beyond Jupiter cannot effectively rely on photovoltaic panels for energy, because the great distance to the Sun means that the amount of solar radiation per unit of area is very low, requiring impractically large (and thus heavy) panels to provide enough energy. Carrying a lot of fuel adds mass to the probe, making them more expensive to launch.
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There are devices that need substantial electrical power over long time – in the order of decades – but local sources of energy are insufficient or unavailable, yet constructing a power line or resupplying them with some power source (like fuel, fresh chemical batteries etc.) is either impossible or overly costly. Such devices include maritime beacons and buoys, automatic weather and science stations located in remote areas, and – most importantly – deep space probes and some planetary probes or science packs. Probes sent beyond Jupiter cannot effectively rely on photovoltaic panels for energy, because the large distance to the Sun means that the amount of solar radiation per unit of area is very low, requiring impractically large (and thus heavy) panels to provide enough energy. Carrying a lot of fuel also adds mass to the probe.
  
Instead, such devices usually use {{W|radioisotope thermoelectric generator}}s (RTGs). In an RTG the natural radioactive decay of some unstable isotope (such as {{w|plutonium-238}} or {{w|strontium-90}}) produces a lot of heat, which is then used to generate energy using {{W|thermopile}}s, which generate electricity directly from temperature differences using the {{W|thermoelectric effect}}. The key element of an RTG, a pellet of radioactive material such as plutonium dioxide, could be facetiously described as a "power orb" – a lump of a substance that gives out heat apparently out of nothing. For example, the Voyager probes used three RTGs, each containing 4.5kg of plutonium-238, each producing at its peak 2400W of heat energy, converted to 160W of electrical energy.
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Instead, such devices usually use {{W|radioisotope thermoelectric generator}}s (RTGs). In an RTG the natural radioactive decay of some unstable isotope (such as Plutonium-238 or Strontium-90) produces a lot of heat, which is then used to generate energy using {{W|thermopile}}s, which generate electricity directly from heat (actually temperature gradients) by employing the {{W|thermoelectric effect}}. The key element of an RTG, a pellet of radioactive material such as plutonium dioxide, could be facetiously described as a "power orb" – a lump of a substance that gives out heat apparently out of nothing.
  
Plutonium-238 must be produced from uranium in a nuclear reactor.  Unlike plutonium-239, the {{W|Alpha decay|alpha radiation}} emitted by plutonium-238 is relatively harmless, as it is quickly absorbed by surrounding material and turned to heat – but plutonium is still incredibly dangerous if it gets inside a human body unprotected. In pure form it produces a little more than half a watt of heat per gram, which slowly drops as the material decays to lead, emitting a quarter watt per gram after 100 years. Other disadvantages of RTGs include the risk of contamination in the event of a launch failure, and the relatively limited supply of plutonium.
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Note that the radioactive material obviously doesn't produce this energy forever, although it can produce it so long the device will break before it gets out of energy. Mentioning this detail might make it seem more realistic ... on the other hand, mentioning that it stops producing energy because it transforms to lead might actually sound even less realistic to person who doesn't know how it works.
  
The title text references development of games. A rule or strategy within a game is often called a ''mechanic'', meant as one particular rule (singular) out of the overall set of rules (game mechanic''s''). In this context, the word ''mechanics'' is a metaphor referring to the set of rules and interactions that govern the imaginary world of the game. The ''mechanics'' of a game define the deterministic or randomized functions of events and/or characters within the game, the outcomes of actions commanded by the players, and so on. This metaphor refers to the {{W|mechanics}} science, and how it describes behavior of physical objects in the real world; However, contrary to real-world mechanics which "just happen" and we only try to describe how things work, in {{W|game mechanics}} every single rule or interaction has to be explicitly defined. The game simulates (to a given extent) an actual world. Game rules do not need to mimic the real world closely and often don't for many reasons; This results in (intended or otherwise) inconsistencies, unexpected behavior or imbalance. Game players complain about “imbalance” when a particular rule, interaction or item present in the game (such as an extremely powerful magical artifact) gives a character exploiting it a great and unjustified advantage. Inconsistencies and possible imbalances can lead to problematic game mechanics being unused or left unresolved, after the creator of those mechanics ceases their participation in the game or game development process.
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The title text references development of team-written episodic stories, such as video games, television shows, or comic series, and how after joining a team and implementing a mechanic, a writer can leave, and give others working on it little or no knowledge of how to handle a specific plot element or design.
 
 
Things that seem like they shouldn't work but do are the main topic of [[2540: TTSLTSWBD]].
 
  
 
==Transcript==
 
==Transcript==
 
 
:[Megan, Hairy, Cueball, and Ponytail are talking.]
 
:[Megan, Hairy, Cueball, and Ponytail are talking.]
 
:Megan: How will we keep the spacecraft supplied with heat and electricity?
 
:Megan: How will we keep the spacecraft supplied with heat and electricity?
 
:Cueball: We could use a power orb. They give off thousands of watts 24/7.
 
:Cueball: We could use a power orb. They give off thousands of watts 24/7.
:Megan: Huh? How do you recharge it?
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:Megan: Huh? How do you recharge it.
 
:Cueball: You don't. It's just made of a metal that emits energy.  
 
:Cueball: You don't. It's just made of a metal that emits energy.  
 
:Megan: OK, come on.
 
:Megan: OK, come on.
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:[Caption below the panel:]
 
:[Caption below the panel:]
 
:For something that's real, plutonium is so unrealistic.
 
:For something that's real, plutonium is so unrealistic.
 
==Trivia==
 
*{{w|Kerbal Space Program}}, a space simulator game which has been featured in xkcd several times, has its own version of the RTG, running on Blutonium-238. However, due to the lack of a half-life mechanic, the RTG is simply an infinite source power – an actual videogame power orb. Randall has made [[:Category:Kerbal Space Program|several references]] to the game.
 
  
 
{{comic discussion}}
 
{{comic discussion}}

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