Talk:2906: Earth

I originally read the caption as "how badly we'd messed up", which... changes Sagan's tone somewhat. 172.71.155.54 08:02, 14 March 2024 (UTC)

At first I thought the joke was that the rocket firing had somehow gone so catastrophically badly that the entire Earth had literally been reduced to dust. Fabian42 (talk) 08:37, 14 March 2024 (UTC)

I also had this notion at first. That after the failed burn Earth had been destroyed... But I think not so anymore. So thx explain xkcd. ;-) --Kynde (talk) 12:43, 14 March 2024 (UTC)

So, according to explainxkcd, that’s a square “spacecraft window”?? Why have we never seen a square spacecraft window in any other context, ever? Did Randall screw up that badly in the original comic, or was it a previous explainxkcd editor who screwed up here? 172.70.214.60 08:58, 14 March 2024 (UTC)

I'm not sure what you're on about and why anyone has to have screwed up. Why can't it be a rectangular (we don't know it's square) spacecraft window? Bischoff (talk) 09:53, 14 March 2024 (UTC)

This is very clearly a triangle shaped window in a very elongated spaceship Whimsical (talk) 11:24, 14 March 2024 (UTC)

Maybe it is part of a huge spider-shaped window? (I home people here will remember that meta-reference to What If) 172.71.94.208 12:28, 14 March 2024 (UTC)

This picture from the Cupola module of the ISS has trapeze like windows. But the one behind the astronaut could easily have been a rectangle from what can be seen in the picture. So to argue that this window could not have been shot the same is just silly. Of course it was important to the joke that you did not realize it was a window until reading the caption. Also if this space craft has held up to go so far form Earth with living inhabitants it is obviously not a space ship in use today! --Kynde (talk) 12:43, 14 March 2024 (UTC)

There is precedent with the Space Shuttle (aft flight-deck window, others were round, the 'forward flight-deck' ones were of course the main flight/piloting ones with awkward quadrilateral shapes and pesky instrument panels where none are in the comic). The windows in the Shuttle were actually a weight issue (certainly, at first, they were plain (chunky!) glass, and added a lot of weight to the design.

Also look at Blue Origin's capsule for more current design that could end up eventually on an orbital/extra-orbital vessel. Although Crew Dragon is more conservative, and Orion's interior looks like it isn't so big (while Starship's eventual window configuration might eventually be vastly more conservative than the Dan Dare/Flash Gordon aesthetic of the concept imagery).

So... Possible, but depends upon the design needs for the craft (fully space-capable whilst intended to undergo re-entry, is all we really know). 172.70.90.92 16:13, 14 March 2024 (UTC)

In my mind is the scene in C.S. Lewis's religious novel Out of the Silent Planet, where an English philologist, Ransom, is abducted by criminals into outer space and meets aliens. In chapter fifteen, a wise sorn tries to figure out which planet Ransom is from. Probably Thulcandra, the garbage planet of the Solar System. Ransom doesn't like the sound of that, but the sorn gets out something that isn't a telescope and he shows Thulcandra to Ransom, and yup, that's us. Lewis writes it better. I don't know if Carl Sagan had read this. --Robert Carnegie [email protected] 141.101.99.75 13:12, 14 March 2024 (UTC)

Hoo boy, yep that book (and its sequel) are beyond even Narnia in their religious symbolism (though the later environmentalist movements could definitely find an allegory in them, too, not sure how intended that was, in CSL's time, some time before a practical Gaia Hypothesis/etc). I can imagine Randall knows of the book (though clearly more influenced by Sagan in a direct lineage). Not entirely sure Sagan will have taken interest in that genre, nor taken the above to heart. Probably no more than his genuine scientific and rhetoric interests, which may be sufficient genesis for his own coined meme. But that's just my gut feeling. i.e. Worthy of note, but not directly (or singly-indirectly) connected. 172.70.85.153 14:20, 14 March 2024 (UTC)

The Gaia Hypothesis is also religious, so it makes sense that it could be written into C. S. Lewis. Protecting the environment is important, but Mother Nature is basically a deity for misanthropes. 162.158.155.91 (talk) 14:02, 15 March 2024 (please sign your comments with ~~~~)

It can be believed religiously, and is named after a goddess, but also can be used to describe the (long-term) self-regulating interactions of the various elements of biomes and atmos/geos-/pedospheres that interact, in a more scientific way. (Some people religiously believe in evolution as God's "fire and forget" Creationist act to get us from the very start of Genesis until Revelations, for example, but it doesn't stop a strictly agnostic scientific analysis of natural selection getting us here, with or without writings that describe everything in traditional concepts that may not necessarily' be entirely accurate - but sustained "God's chosen people" in ways that mattered... to put just one teleological spin on it.)

It can just be considered a more complex (and entirelg natural) global thermostat. Which might have difficulty dealing with people lighting unexpected fires in the middle of their bedrooms (e.g.), and can't stop them burning their own house down if they start a runaway effect that it has no power to stop, but normally it can counteract variations of temperature by eventually adjusting the heating/cooling elements. Or, I suppose, decides that a hotter/colder house is better, so long as there are still some pot-plants that will thrive under the new conditions (until nudged back by other effects).

...that's simplistic, as an analogy, and in key ways 'not really correct', but it starts to reflect the no-god-needed tenet of the general idea. (Not sure I have confidence in "it'll be alright", but I would say it has better chance than "we'll be alright", as we aren't vital to 'keep things going'. In fact, once we're gone then anything that remains will get its own chance to nudge conditions to a new equilibreum.) 141.101.98.232 15:23, 15 March 2024 (UTC)

The color for the blue dot seems to be around #B6C8EB. --1234231587678 (talk) 15:18, 14 March 2024 (UTC)

Zooming in, the central pixel is definitely #ABBBDC (a very easy color to hand type), with some artifacts around it of varying shades of grey. 172.69.59.184 20:58, 14 March 2024 (UTC)

I think we're discussing different versions of the two images. The single central pixel of the dot in the "regular-sized" image on the xkcd site, "earth.png" (364 x 472 pixels), is now #B5C6E9, while the six central pixels in the 2x image, "earth_2x.png" (728 x 945 pixels), are #BDCFF4. The "regular-sized" version here, "363px-earth_2x.png" (363 x 471 pixels) has a single central pixel, #ABBBDC, while the large image on *this* site, "545px-earth_2x.png" (545 x 707 pixels), has two central pixels, #BDCFF4. BunsenH (talk) 22:33, 14 March 2024 (UTC)

I'd say he nailed Sagan's hair... Inexplicable (talk) 19:11, 14 March 2024 (UTC)

Carl may *claim* to have messed up, but I find it hard to believe that he wouldn't aim the rocket for deep space, given half a chance.

Sounds about right. It's Carl Sagan... and besides, who wouldn't want the opportunity to venture into the final frontier? (Also, please remember to sign your post next time.) OmniDoom (talk) 23:40, 14 March 2024 (UTC)

Um. "Spend a little while in LEO then go home and live out the rest of your life" vs. "spend a little while much further out, in the company of a few people who really resent you, then die unpleasantly"? I'd go with the former. BunsenH (talk) 16:18, 15 March 2024 (UTC)

Does anybody know what is a typical reentry burn, for instance, when a capsule leaves the ISS? I wrote "some hundreds m/s" but it might be less than that. If the original orbit is very low, even a tiny reduction will lower the perigee enough to intersect the atmosphere. Rps (talk) 18:57, 18 March 2024 (UTC)

According to What If: Orbital Submarine, "A typical de-orbiting maneuver requires in the neighborhood of 100 m/s of delta-v, which means that the 24 Trident missiles carried by an Ohio-class submarine could be just enough to get it out of orbit." Take The A Train To Watertown (talk) 00:20, 20 March 2024 (UTC)

Most treatments I see of the respective Delta-V Budgets basically deal with having to overcome the atmospheric and gravity deficits upon launch to LEO, which don't easily apply/discount in reverse. Also the delta-v needed betwixt low-LEO and high-LEO (or roughly encompassing the difference between current space-stations and a Hubble servicing mission) is almost a full km/s (either way), so you might need to add that to the much smaller(?) final bit of atmosphere-hitting adjustment, whereupon you hopefully are now slowing down entirely passively. (Rather than bouncing off...)

If you can afford to wait, though, being at ISS heights will bring you down with zero (active) delta-v. There being tenuous atmosphere, already, that actually requires maintenance boosts every now and then to keep it up there. So maybe you need to consider it much as you do with a launch profile (over-powered rocket first-stage gets you over the atmospheric 'hump' quicker, and requires less total delta-v expendes for the same eventual mission). But the ultimate solution (entirely hand-brake your orbit, just fall straight down from space itself) is also not practical or necessary.

All in all, your "some hundreds m/s" is probably not far wrong.

Perhaps chase down the Crew Dragon operating manual, as a current example, if you want to put such actual figure(s) as used. Not sure how public that info is, but there are a lot of armchair experts out there that particularly reverse engineer vague SpaceX release-info into solid-looking figures that Musk then confirms "sound about right" if he responds to their assessments. If the usual suspects haven't crunched this number, then I'd be surprised. 172.69.195.38 05:24, 19 March 2024 (UTC)

I played around a bit with my DIY orbit calculator LITHOBREAK, to go from a 300x300 km orbit (calculated above the surface) to a 300x100km one, which puts your perigee inside the upper atmosphere, you need a Delta-V of 59m/s. To raise your apogee to about GEO, you need roughly 2400 m/s. I could be wrong (cobbled the tool togehther a long time ago), but it looks just about right. --172.68.50.120 06:06, 11 April 2024 (UTC)

My reading: The original plan for Voyager 1 was it, after LEO to complete its mission and to be destroyed by burning in the atmosphere. So, all the spectacular discoveries of Voyager 1, including the Pale Blue Dot, are unintentional results of Cara’s miscalculations. Contrary to popular opinion, the Carl’svcoworkers are deeply disappointed that Voyager didn’t burn. 162.158.60.145 12:43, 19 March 2024 (UTC)