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Explain xkcd: It's 'cause you're dumb.
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To motivate it to fire its harpoons hard enough, Rosetta's Philae lander has been programmed to believe it is trying to kill the comet.
Title text: To motivate it to fire its harpoons hard enough, Rosetta's Philae lander has been programmed to believe it is trying to kill the comet.


Ambox notice.png This explanation may be incomplete or incorrect: Needs more work, especially the top section.
If you can address this issue, please edit the page! Thanks.

Continuing a recurring theme (as seen in comics 111, 231, and 323), two unrelated but interesting objects have been juxtaposed graphically with humorous results. In this case, it's the fact that old-timey, man-made harpoons (a cool word) have been placed among the equipment for a space flight (a cool concept). According to Randall, this has happened twice.

The latter peak on this graph refers to the Rosetta unmanned spacecraft. As part of its mission, it's carrying a lander (called Philae), which has two tethers to anchor itself to the comet 67P/Churyumov–Gerasimenko. Rosetta was launched in March 2004 (as shown in the graph) and is scheduled to encounter the comet in August 2014, making this a timely comic.

The first peak is probably a joke. Officially, Apollo 12 carried neither harpoons nor rum. However, as a former NASA contractor, Randall may know more about space shenanigans than the general public, and may be implying (perhaps jokingly) that a bottle of the Harpoon brand of Jamaican rum made it aboard.

The title text compares the Philae lander's method of deploying its tethers to whaling, in which sailors would throw harpoons at a whale with the intent of killing the whale. It was important to throw hard so the harpoon would stick in the whale so it could not get away and would tow the whaling boat until it got tired and could be killed.

It is implied that the spacecraft is sentient and needs a motivation to fire the harpoons hard enough to stay anchored to the comet. It has thus been programmed to believe that its mission is to kill the comet. This is a joke, as Rosetta is of course not sentient[Citation needed].


Number of harpoons in space
by year
[A chart with a red graph is drawn below]
[The y-axis]
0 1 2 3
[The x-axis]
1950 1960 1970 1980 1990 2000 2010 2020
[The graph is at zero until a sharp peak to 1 in 1970. The peak is labeled]
Apollo 12 rum incident
[The graph then stays at 0 until 2004. Then it rises to 2 and stays there until today, continuing as a dotted line after 2014. The rise is labeled]
Rosetta comet mission launched carrying lander with harpoon tethers

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