Main Page

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search

Welcome to the explain xkcd wiki!
We have an explanation for all 2533 xkcd comics, and only 32 (1%) are incomplete. Help us finish them!

Latest comic

Go to this comic explanation

Retractable Rocket
Hard to believe that for so many years once they were fully extended we just let them tip over.
Title text: Hard to believe that for so many years once they were fully extended we just let them tip over.

Explanation

Ambox notice.png This explanation may be incomplete or incorrect: 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 absurdist ventures. He explains to Megan that "we" (possibly his company) are testing their new "retractable" rocket.

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.

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 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.

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.

A possibility of making a 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.

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.

This comic was released ahead of (and possibly refers to) SpaceX's Crew-3 mission to send astronauts to ISS with a reusable rocket on 31 October 2021.

Transcript

[Beret Guy and Megan is talking. Behind them near the horizon is a tall rocket on a launchpad.]
Beret Guy: We're testing our new retractable rocket.
Megan: You mean reusable?
Beret Guy: No.
[A zoom in on the launchpad and rocket. It has the appearance of having a long first stage, a second stage with slightly wider fairing and an Apollo-style capsule with escape-tower atop it all. There is a directionless speech-bubble at the top depicting a count down voice.]
Count down: Three...Two...One...Liftoff!
[Same view as before, but while the base of the rocket-stack remains stationary, the first stage is apparently elongated, with a hint of a bend to the right, to raise the total height to which the upper-stage and capsule assembly reaches almost to the top of the panel.]
[In a wider panel, with the base to the left, the first stage is now elongated far enough to disappear off the top of the center of the frame, thus clearly bending to the right. Two peoples voices are indicated as coming from the space capsule far above, as it reaches it destination.]
Voice 1: Hi, welcome to the ISS!
Voice 2: Hello!
[The final panel shows the same view as in the third panel. The first stage is now retracting, and has similar length as in the third panel, but the capsule is no longer atop the 'second stage' fairing. Four movement lines above the top of the retracting rocket indicates that it is returning back to the original position.]

Trivia

  • The original comic misspelled "retractable" as "retractible". Has been documented on the web archive.
    • This was done both in the comic itself, and the title.
    • This was soon corrected, but has left it's mark on explain xkcd as can be seen in the links above.


Is this out of date? Clicking here will fix that.

New here?

Last 7 days (Top 10)

Lots of people contribute to make this wiki a success. Many of the recent contributors, listed above, have just joined. You can do it too! Create your account here.

You can read a brief introduction about this wiki at explain xkcd. Feel free to sign up for an account and contribute to the wiki! We need explanations for comics, characters, themes and everything in between. If it is referenced in an xkcd web comic, it should be here.

  • There are incomplete explanations listed here. Feel free to help out by expanding them!
  • We sell advertising space to pay for our server costs. To learn more, go here.

Rules

Don't be a jerk.

There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.

If you want to talk about a specific comic, use its discussion page.

Please only submit material directly related to (and helping everyone better understand) xkcd... and of course only submit material that can legally be posted (and freely edited). Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.

If you need assistance from an admin, post a message to the Admin requests board.