explain xkcd - User contributions [en]

Talk:1660: Captain Speaking

2016-03-25T16:00:34Z

162.158.56.5: added discussion note

Actually captain falling asleep wouldn't be unlikely or problem because there may still be two OTHER people in cabin. But yes, first method to find out where they are going would be to ask those other people in cabin. Next, you should be able to get something from the instruments in cabin - I suspect that modern planes DO have some sort of navigation map there. Failing that, asking tower for flight plan would be not only preferable to trying FlightAware, but you could likely do it without raising TOO much suspicious, pretending you just need some detail.
And, yes: captain (or pilot in general) is only needed for pre-flight checks, take-off, landing - and if something unexpected happens, including some extremely bad weather. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 14:53, 25 March 2016 (UTC)

Yeah it was badly phrased, pilots do fall asleep from time to time. Some long flights may even have two flight crews, so the pilots can get some shut-eye. It varies, but there is '''never''' only one person alone in the cabin as you say, if the co-pilot has to go to the toilet a flight attendant takes his place. As for positioning, older planes have instruments for that too, but they are far less sophisticated, might even require a map and a pencil :-) --[[User:Todor|Todor]] ([[User talk:Todor|talk]]) 15:59, 25 March 2016 (UTC)

Just noting, the discussion shows up on main again. [[Special:Contributions/162.158.56.5|162.158.56.5]] 16:00, 25 March 2016 (UTC)

1244: Six Words

2016-02-02T20:57:23Z

162.158.56.5: Undo vandalization in revision 110435 by 108.162.221.4 (talk)

{{comic
| number = 1244
| date = July 29, 2013
| title = Six Words
| image = six words.png
| titletext = Ahem. We are STRICTLY an Orbiter shop.
}}

==Explanation==
The six words are "It works in ''Kerbal Space Program''".

The {{w|Kuiper Belt}} is a region of the outer Solar System beyond the orbit of Neptune consisting of numerous small icy bodies, including the dwarf planets {{w|Pluto}} and {{w|Eris (dwarf planet)|Eris}}. An {{w|Oberth effect|Oberth maneuver}} is a spaceflight maneuver, specifically an engine burn performed during the flyby of a celestial body. The point of this is to optimize usable energy, because rocket burns are more effective to perform at high speeds than at low speeds. The more massive the body and the lower the altitude, the higher the flyby speed will be, and the greater the performance gain due to the Oberth effect. The theoretical way to use rocket fuel most efficiently is therefore to execute the burn during a flyby of the most massive celestial body available, as close as possible.

[[Cueball]] is proposing to implement an "Oberth Kuiper Maneuver", and the proposal diagram shows the spacecraft using {{w|Gravity assist|gravity assists}} to travel first towards (presumably) {{w|Venus}} for a first boost, then towards a distant planetary object for another swing by, aiming it back towards the {{w|Sun}}, the most massive Solar System body, to perform an Oberth maneuver at the point of closest approach, as indicated by a small dot along the spacecraft trajectory. (The objects in the diagram are unmarked, and the identity of the distant planetary object is controversial. One possible interpretation is that it is a Kuiper Belt object, referred to by the word "Kuiper" in the name of the proposal. Another possible interpretation is that it is {{w|Jupiter}}, and the word "Kuiper" references the Kuiper Belt as the intended destination of the spacecraft after the maneuver. (See the discussion for arguments for either interpretation.) It is possible that the diagram might only be a simplified outline of a more complex flight plan. For example, the trajectory from Earth to Venus would require two separate burns in deep space. The first burn would occur immediately after escaping Earth's sphere of influence. The second burn would occur about halfway to Venus. Alternatively, Cueball may have gotten it wrong, or [[Randall]] may simply not have concerned himself with such things for the purpose of a webcomic sketch.

An Oberth maneuver in the close vicinity of the Sun, while theoretically possible and extraordinarily effective at the speeds the spacecraft would reach, would however be very difficult to carry out in real life, because the neighborhood of the Sun is an extremely hostile environment and the spacecraft could be incinerated during a too-close flyby.

Cueball's argument for why the maneuver will work in real life is that it works in ''{{w|Kerbal Space Program}}'' (KSP), a sandbox spaceflight simulator. While KSP does take into account quite a bit of the physics of space flight, it is (necessarily) simplistic in its modeling of orbital dynamics. KSP does not make any attempt to deal with the {{w|N-body problem}} (for which there is no complete solution), or even simpler 2-body mechanics. Instead celestial bodies are "on rails" and have fixed {{w|Sphere of influence (astrodynamics)|Spheres of Influence}} (SOI); a craft within a particular SOI feels the gravitational influence of only that body, and transitions are abrupt when a craft crosses the edge of an SOI. This means there are no {{w|Lagrangian point|Lagrangian points}}, {{w|Lissajous orbit|Lissajous orbits}}, or, critically for this context, {{w|Orbital perturbation analysis (spacecraft)|orbital perturbations}} by distant bodies or other factors. Therefore orbits modeled using KSP would poorly reflect the actual orbital behavior of a probe traveling through the solar system on a multi-year mission involving multiple fly-by maneuvers.

The humor in referencing KSP in the comic lies in using a simple game program to simulate complex space missions which in reality take a great number of experts to plan and implement. Fly-by maneuvers, used to minimize the fuel needed to reach a destination, need to be very carefully timed - often to within seconds - so the use of ''Kerbal Space Program'' to simulate them isn't a good enough argument for NASA to agree to implement the proposal, and implies simplistic thinking on the part of the proposer; therefore one should not say it at NASA.

The title text refers to ''{{w|Orbiter (simulator)|Orbiter}}'', which is another spaceflight simulator program. The title text suggests that the argument doesn't work for NASA, not because it's not scientifically sound, but because NASA relies on the ''Orbiter'' simulator rather than the ''Kerbal'' simulator (although the proposed maneuver would appear to work in both). Note, however, that [http://news.cnet.com/8301-1023_3-57495117-93/mars-curiosity-rover-team-prefers-macs-to-pcs/ a few team members "love" to play ''Kerbal''].

==Transcript==
:[Caption above the frame:]
:The six words you ''never'' say at NASA:

:[A diagram shows a trajectory path starting at Earth and involving two slingshots around two other planets, and finally the Sun. There is a label beneath the diagram. The diagram is being presented by Cueball in front of three other Cueball-like guys. Behind Cueball Ponytail appears to be taken by surprise by his six words, and holds her hand to her mouth.]
:Label: Oberth Kuiper Maneuver

:Cueball: And besides—
:Cueball: It works in Kerbal Space Program.

==Trivia==
*{{w|NASA}} is planning a mission to the sun at a closest distance of only 8.5 solar radii. The {{w|Solar Probe Plus}} will use seven Venus flybys to reach its [http://solarprobe.jhuapl.edu/index.php first close approach]. The maneuvers will last nearly seven years, before the real mission does start.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Multiple Cueballs]]
[[Category:Physics]]
[[Category:Space]]
[[Category:Video games]]

Talk:1633: Possible Undiscovered Planets

2016-01-23T05:27:27Z

162.158.56.5: During the day = star.

Why is it late? — ''[[User:Tbc|tbc]] ([[User talk:Tbc|talk]]) 16:57, 22 January 2016 (UTC)''
:No idea but it's weird. [[User:SuperSupermario24|<span style="color: #c21aff;">Just some random derp</span>]] 18:08, 22 January 2016 (UTC)

Why is Earth's "Distance from me" 10000km? -- ''19:26, 22 January 2016 (UTC)''
:The diameter of Earth is ~12000km and distances are measured from the center of the object (that why there is a "Planet ruled out because I would be inside them" zone). I suppose Earth should be placed at a distance of 6000km instead of 12000k (as it is the radius, not the diameter that matter here). [[Special:Contributions/141.101.66.11|141.101.66.11]] 19:43, 22 January 2016 (UTC)
::Earth's distance seems to be to the left of the 10Mm marker on the distance line, to me, although it's hard to tell without a straightedge. Remember the plot is diameter to distance. [[Special:Contributions/108.162.238.71|108.162.238.71]] 19:52, 22 January 2016 (UTC)

This comic bothers me because the diagonal line with Earth on it cannot possibly represent what it claims. Zero cannot be plotted on the X-axis with this log scale. The entire "I would be inside of them" region is bogus. [[Special:Contributions/188.114.106.83|188.114.106.83]] 19:42, 22 January 2016 (UTC)
:Not if you're measuring to the center of the planet. [[Special:Contributions/108.162.238.71|108.162.238.71]] 19:52, 22 January 2016 (UTC)
:Also, please sign your comments. I had to sign this one for you. [[Special:Contributions/108.162.238.71|108.162.238.71]] 19:54, 22 January 2016 (UTC)
:OK, it does make sense if you take the normal convention of arrival and turn it into total core penetration. Sorry about the signing thing. I never use this and wondered where the input for it was. I see now from googling around that you just put it at the end. [[Special:Contributions/188.114.106.83|188.114.106.83]] 20:00, 22 January 2016 (UTC)

Planets ruled out because we could see them during the day = Stars? [[Special:Contributions/162.158.56.5|162.158.56.5]] 21:10, 22 January 2016 (UTC)
: Only stars that are close enough to see during the day. Actually, there's one star that ''is'' close enough that we can see it during the day, although for some reason Randall did not mark it on the chart: our Sun. (Every other star is so far away that it's off the chart.) —[[User:TobyBartels|TobyBartels]] ([[User talk:TobyBartels|talk]]) 21:34, 22 January 2016 (UTC)
::I added the stars statement before reading your comment. Feel free to edit it.
::And I agree that it's strange that Randall didn't mark the Sun. Furthermore, the Sun fits the Greek definition of planet. In fact, it fits any definition of planet better than birds or planes.--[[User:Pere prlpz|Pere prlpz]] ([[User talk:Pere prlpz|talk]]) 21:57, 22 January 2016 (UTC)

: No not stars, this is just about planets -- you can see the moon in the day when in the right position compared to the sun. You would be able to see any planet during the day if the circular surface was sufficiently big, and with a planetary body that is a function of the size over the distance squared -- the moon is just so close that it does not have to that big [[Special:Contributions/162.158.255.109|162.158.255.109]] 22:25, 22 January 2016 (UTC)

:: So shouldn't the "during the day" section be sloped, and include the moon? --[[Special:Contributions/162.158.252.227|162.158.252.227]] 23:41, 22 January 2016 (UTC)

::I think during the day means stars. You get much bigger on the diameter axis then Jupiter, and it starts undergoing fusion, which we could see "during the day" even at far distances because they would be providing light themselves. Get it?[[Special:Contributions/162.158.56.5|162.158.56.5]] 05:27, 23 January 2016 (UTC)

I think Randall means "TENTH planet". 22:58, 22 January 2016 (UTC)
: Yawn. I think you're trolling. [[Special:Contributions/198.41.238.32|198.41.238.32]] 03:08, 23 January 2016 (UTC)

The subtitling of planes as "Fool's Planets" is clearly intended to be analogous to "Fool's Gold", the mineral that looks a lot like gold to the (non-expert) eye. That is, if there's a bright spot of light in the sky (usually just before dusk or just after dawn) then it might be mistaken for a planet like Venus, but instead just be the glimmer of near-horizontal sunlight off of a wing-front or body-edge of plane too high to discern a shape/silhouette against the sky, too far away to see coloured navigation lights and just happens not to be leaving a contrail. At a glance, you might assume it was something astronomical. Only by keeping an eye on it could you be sure to discern relatively rapid (perhaps non-ecliptic) movement and other details that would at least suggest it was no higher than a satellite. (Of course, it would be techncally be a UFO, leastways until you actually identified it sufficiently.) [[Special:Contributions/162.158.152.89|162.158.152.89]] 00:24, 23 January 2016 (UTC)

Also, note the implication that Randall would keep Giant Bugs at least 100m away from him, at all times. Doubtless by running away. (Or else by closing the doors and windows of his 100m-radius house and hiding himself away under blankets in its centre???) 00:29, 23 January 2016 (UTC)

I think the three lower planet dots are from left to right, Venus, Mars, Mercury based on their diameters which (unlike their distances from Randall) are invariant. [[User:Co149|Co149]] ([[User talk:Co149|talk]]) 02:22, 23 January 2016 (UTC)
: I agree that based on the Y-axis position, the order is Venus, Mars, Mercury. The relative sizing of the circles is misleading.[[Special:Contributions/108.162.237.68|108.162.237.68]] 04:08, 23 January 2016 (UTC)

Talk:1633: Possible Undiscovered Planets

2016-01-22T21:10:47Z

162.158.56.5: Category not explained

Talk:1608: Hoverboard

2015-11-24T23:24:30Z

162.158.56.5:

Well, this will be the next incomplete explanation for a while. -[[Special:Contributions/162.158.90.165|162.158.90.165]] 21:58, 24 November 2015 (UTC)

Yes, one thing to note is how to get the hell out of the cave near the volcano [[Special:Contributions/108.162.249.159|108.162.249.159]] 22:38, 24 November 2015 (UTC)

The image is made up of small images with addresses of the form http://xkcd.com/1608/XXXX:-YYYY+s.png (although not every coordinate inside the bounds has an image associated). A script could probably dump out all the images and paste them together. --[[Special:Contributions/108.162.216.6|108.162.216.6]] 22:46, 24 November 2015 (UTC)

West -- Under Lava Pools -- Elon Musk's Secret Volcano Base (not as enjoyable as you might expect).

The Starship out east contains, among other things, Darth Vader, apparently explaining Steven Universe to a subordinate. (Steven and the Crystal Gems can be found a the west end of the ship, near an ice cream cooler.) The same ship contains an elaborate homage to the original Prince of Persia.

There, have at thee an image! [[User:Arch-TK|Arch-TK]] ([[User talk:Arch-TK|talk]]) 22:58, 24 November 2015 (UTC)

There are 168 coins spread throughout the map according to the source code [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:03, 24 November 2015 (UTC)

When using a device, instead of saying "use arrow keys to move", it says "tilt to move, tap to jump". It's also a lot harder to control.

It's actually 169 coins (t.length). --[[Special:Contributions/188.114.111.129|188.114.111.129]] 23:22, 24 November 2015 (UTC)

Talk:1608: Hoverboard

2015-11-24T23:10:24Z

162.158.56.5:

Well, this will be the next incomplete explanation for a while. -[[Special:Contributions/162.158.90.165|162.158.90.165]] 21:58, 24 November 2015 (UTC)

Yes, one thing to note is how to get the hell out of the cave near the volcano [[Special:Contributions/108.162.249.159|108.162.249.159]] 22:38, 24 November 2015 (UTC)

The image is made up of small images with addresses of the form http://xkcd.com/1608/XXXX:-YYYY+s.png (although not every coordinate inside the bounds has an image associated). A script could probably dump out all the images and paste them together. --[[Special:Contributions/108.162.216.6|108.162.216.6]] 22:46, 24 November 2015 (UTC)

West -- Under Lava Pools -- Elon Musk's Secret Volcano Base (not as enjoyable as you might expect).

The Starship out east contains, among other things, Darth Vader, apparently explaining Steven Universe to a subordinate. The same ship contains an elaborate homage to the original Prince of Persia.

There, have at thee an image! [[User:Arch-TK|Arch-TK]] ([[User talk:Arch-TK|talk]]) 22:58, 24 November 2015 (UTC)

There are 168 coins spread throughout the map according to the source code [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:03, 24 November 2015 (UTC)

Talk:1608: Hoverboard

2015-11-24T23:06:39Z

162.158.56.5:

Well, this will be the next incomplete explanation for a while. -[[Special:Contributions/162.158.90.165|162.158.90.165]] 21:58, 24 November 2015 (UTC)

Yes, one thing to note is how to get the hell out of the cave near the volcano [[Special:Contributions/108.162.249.159|108.162.249.159]] 22:38, 24 November 2015 (UTC)

The image is made up of small images with addresses of the form http://xkcd.com/1608/XXXX:-YYYY+s.png (although not every coordinate inside the bounds has an image associated). A script could probably dump out all the images and paste them together. --[[Special:Contributions/108.162.216.6|108.162.216.6]] 22:46, 24 November 2015 (UTC)

West -- Under Lava Pools -- Elon Musk's Secret Volcano Base (not as enjoyable as you might expect).

The Starship out east contains, among other things, Darth Vader, apparently explaining Steven Universe to a subordinate.

There, have at thee an image! [[User:Arch-TK|Arch-TK]] ([[User talk:Arch-TK|talk]]) 22:58, 24 November 2015 (UTC)

There are 168 coins spread throughout the map according to the source code [[Special:Contributions/173.245.54.53|173.245.54.53]] 23:03, 24 November 2015 (UTC)