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==Explanation==
 
==Explanation==
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{{incomplete|Created by a RETRACTABLE ROCKET SCIENTIST - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
  
 
This comic documents another of [[Beret Guy]]'s [[:Category:Strange powers of Beret Guy|absurdist ventures]]. He explains to [[Megan]] that "we" (possibly [[:Category:Beret Guy's Business|his company]]) are testing their new "retractable" rocket.  
 
This comic documents another of [[Beret Guy]]'s [[:Category:Strange powers of Beret Guy|absurdist ventures]]. He explains to [[Megan]] that "we" (possibly [[:Category:Beret Guy's Business|his company]]) are testing their new "retractable" rocket.  
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{{w|Reusable launch system|Reusable rockets}} are a growing industry, as they are more economically viable in the long run – though technically much more difficult to operate – than rocket boosters that are just discarded after use (which have been standard throughout the majority of space-faring history). Thus, Megan is understandably confused about Beret Guy's assertion that theirs is "retractable", asking if he misspoke. In typical fashion, he assures her that he did not misspeak, with a single "No" without further explanation.  
 
{{w|Reusable launch system|Reusable rockets}} are a growing industry, as they are more economically viable in the long run – though technically much more difficult to operate – than rocket boosters that are just discarded after use (which have been standard throughout the majority of space-faring history). Thus, Megan is understandably confused about Beret Guy's assertion that theirs is "retractable", asking if he misspoke. In typical fashion, he assures her that he did not misspeak, with a single "No" without further explanation.  
  
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They proceed to watch the rocket "launch", proving that it is indeed ''retractable''. In fact the rocket does not launch, but merely ''extends'' – apparently all the way to the {{w|International Space Station}} (ISS), a height of over 400 km (over 250 miles) – before retracting, as promised, to its original position. The top part, with the astronauts in it, has been left in space. Presumably, it is docked to the ISS, as the crew onboard the ISS say hello to them in panel 4.
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They proceed to watch the rocket "launch", proving that it is indeed ''retractable''. In fact the rocket does not launch, but merely ''extends'' – apparently all the way to the {{w|International Space Station}} (ISS), a height of over 250 miles (over 400 km) – before retracting, as promised, to its original position. The top part, with the astronauts in it, has been left in space. Presumably, it is docked to the ISS, as the crew onboard the ISS say hello to them in panel 4.
  
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Of course, it would not be possible to extend anything this far.{{Citation needed}} The top would need to be moving very fast compared to the bottom part, or it would bend westwards and break, and even with the strongest material a fully extended, very thin, presumably, hollow structure with a payload on top would {{w|buckling|buckle}} very soon after extension began. Also, the ISS moves at 27,600 km/h (17,100 mph) compared to the ground under it, making an orbit in about one and a half hours. So making the tip follow this long enough to dock would be even more impossible.  
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Of course, it would not be possible to extend anything this far. The top would be moving very fast compared to the bottom part, and even with the strongest material a fully extended, very thin, presumably, hollow structure with a payload on top would break very soon after extension began. Also, the ISS moves at 17,100 mph (27,600 km/h) compared to the ground under it, making an orbit in about one and a half hour. So making the tip follow this long enough to dock would be even more impossible.  
  
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Beret Guy's retractable rocket has more than a few similarities to a {{w|space elevator}} which has been discussed in real life. The chief difference is, a space elevator is only extended once (and most likely this would be down from space, not extended upwards), and never retracted unless it needs to be dismantled. Randall has referenced space elevators in [[697: Tensile vs. Shear Strength]]. A more similar theoretical means to attain orbit is that of the {{w|space fountain}}. He has also examined the problems of a solid metal object extending through the atmosphere [https://what-if.xkcd.com/157/ in a what-if].
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A possibility of making a {{w|space elevator}} has been discussed, but it would not extend like this with a payload on top. Randall has for instance referenced space elevators in [[697: Tensile vs. Shear Strength]].
  
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The current method of sending rockets into space requires huge amounts of fuel, and the more fuel you attempt to carry, the heavier the rocket, leading to more fuel being required, etc. ({{w|Tsiolkovsky rocket equation}}), which makes the current method inefficient.  Alternate methods are being explored, such as using a slingshot ({{w|SpinLaunch}} had a successful test flight of a smaller scale launcher just days before this comic was published, probably the influence for this comic), theoretical {{w|space elevators}}, or this comic's impossible retractable rocket idea, all of which would leave the majority of the "fuel" requirements on Earth or elsewhere rather than having to carry heavy fuel with the rocket.  The only fuel carried might be minimal amounts for course adjustments once in space rather than large amounts used to get there.  However, many of these methods are less flexible than rockets; the space elevator, for instance, operates on the basis of constant angular velocity relative to the Earth's axis of rotation, meaning that it cannot launch payloads directly into low-earth orbit, polar orbits, or many other orbits frequently used by satellites for their desirable characteristics, and satellites intended for these orbits might still need to carry considerable amounts of fuel, even if less than that required to launch directly from the ground.
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The title text parodies the 'old' single-use boosters. It appears that the predecessors to the 'retractable rockets' were capable of controlled extension only. Once they had lofted the payload to orbit, they were then allowed to fall over, destroying them in the process so they could not be used again just like booster rockets. However, if a 250 mile/400 km high construction just fell over, it would be much more difficult to avoid other damage, than to the rocket (booster), than for just a few small booster rockets falling out of the sky.
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The title text parodies the 'old' single-use boosters. It appears that the predecessors to the 'retractable rockets' were capable of controlled extension only. Once they had lofted the payload to orbit, they were then allowed to fall over, destroying them in the process so they could not be used again just like booster rockets. However, if a 250 mile/400 km high construction just fell over, it would be much more difficult to avoid other damage, than to the rocket (booster), than for just a few small booster rockets falling out of the sky.{{Citation needed}}
 
  
 
This comic was released four days before (and possibly refers to) SpaceX's {{w|SpaceX Crew-3|Crew-3 mission}} to send astronauts to ISS with a reusable rocket on 31 October 2021.
 
This comic was released four days before (and possibly refers to) SpaceX's {{w|SpaceX Crew-3|Crew-3 mission}} to send astronauts to ISS with a reusable rocket on 31 October 2021.
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*The [https://web.archive.org/web/20211028014542/https://xkcd.com/ original comic] misspelled "retractable" as "retractible". Has been documented on the web archive.
 
*The [https://web.archive.org/web/20211028014542/https://xkcd.com/ original comic] misspelled "retractable" as "retractible". Has been documented on the web archive.
 
**This was done both in the [https://www.explainxkcd.com/wiki/images/archive/5/57/20211028040721%21retractable_rocket.png comic itself], and [https://www.explainxkcd.com/wiki/index.php?title=2534:_Retractible_Rocket&redirect=no the title].  
 
**This was done both in the [https://www.explainxkcd.com/wiki/images/archive/5/57/20211028040721%21retractable_rocket.png comic itself], and [https://www.explainxkcd.com/wiki/index.php?title=2534:_Retractible_Rocket&redirect=no the title].  
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**This was soon corrected, but has left its mark on explain xkcd as can be seen in the links above.
  
 
{{comic discussion}}
 
{{comic discussion}}

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