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Hijacking DaaaahWhoosh's backstory, let's say our sniper takes the shot anyway, but he accidentally hit one of his weather balloons he set up, and now he's out of tungsten bullets. Frustrated, he decides to go . He pulls at his fishing rod and casts it into a body of water. He then reels up a nice juicy fish. My question is:

  1. What is his fishing rod, line, hook, and bait made out of?
  2. How does he cast it out of orbit?
  3. How accurate did he need to be to have his hook land somewhere with fish?
  4. How strong is he, given he pulled a fish into orbit?
  5. How sensitive does he need to be to feel the fish pulling on the line?

I hope this is possible, for our sniper's sake! There ain't much food is orbit!

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    $\begingroup$ Theoretically he can use fishing rod composed of exotic matter to open up a boom tube and drag a tuna by pulling its mouth with hook. Reality he can ride the space elevator to basement level change into civilian clothing proceeds to level 1 platform reel in a fish and back to basement put on astronaut suit for the fish too and ride the elevator all the way up into space. Magically he can summon the fish! $\endgroup$
    – user6760
    Jul 25, 2015 at 23:50
  • $\begingroup$ Of course... just use a Diamond-Filament line $\endgroup$
    – WernerCD
    Jul 26, 2015 at 3:07
  • $\begingroup$ I was pretty sure this was impossible, but I'm surprised at how many different ways its impossible! $\endgroup$
    – PyRulez
    Jul 26, 2015 at 16:53
  • $\begingroup$ home.comcast.net/~GTOSS/Paper_Lang_GEO_Deploy.pdf -- Describes construction of initial line for a space elevator, closely related to the physics of this problem. They note that active control (rockets) will be needed to guide the initial deployment tether of a space elevator. $\endgroup$
    – Gary Walker
    Jul 26, 2015 at 19:58
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    $\begingroup$ It's easier if the fish is of a species that naturally lives in orbit. $\endgroup$
    – user_1818839
    Jul 26, 2015 at 20:10

8 Answers 8

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  1. His fishing line is carbon nanotubes. Nothing else is strong enough. The rest of it doesn't matter other than the bait has to take the passage through vacuum.

  2. He will need something to cast with. Nobody is strong enough, nobody can move their muscles fast enough.

  3. If he's in a geosynchronous satellite he won't have an accuracy problem--either there's water down there and it works or there isn't and it's hopeless. If he's not in geosync the hook is moving too fast, no fish is going to be able to bite. If the line doesn't go straight down you've got a lot of line on a slant that gravity is trying to straighten--the hook is moving too fast for the fish to catch. Thus he's in geosync.

  4. Pulling the fish into orbit is no big deal. He's got plenty of time to wind in that 25,000 miles of line, boosting the fish to 2mi/sec in the process is of no concern.

    Now, reeling in that line is quite another matter--he's going to have to have a mighty pulley system to do it. He will have starved to death long before the fish is reeled in.

  5. He can't. The line is too long, the fish is long gone by the time any possible signal reaches him. He won't be able to tell it apart from the wind tugging on the line anyway.

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    $\begingroup$ Is it even possible to do anything from orbit =( $\endgroup$
    – Faraz Masroor
    Jul 26, 2015 at 2:40
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    $\begingroup$ No artificial satellites or space stations are tidal lock to Earth, in fact astronaut on ISS will see many sunrises within 24hrs. It is difficult to maintain orbit while playing tug-of-war with a fish, I advise spearing the fish or using a lasso to kidnap the fish😏. $\endgroup$
    – user6760
    Jul 26, 2015 at 4:23
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    $\begingroup$ @user6760 Many, many artificial satellites are geosynchronous. The ISS, no, but satellites, yes. How else do you think the satellite dishes on earth can aim at a satellite, if it’s moving around? $\endgroup$
    – KRyan
    Jul 26, 2015 at 4:40
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    $\begingroup$ @WernerCD It's actually difficult to fall from orbit. You'd definitely need some kind of engine to slow your orbital speed down. A rocket or ion engine or something. $\endgroup$
    – Thane Brimhall
    Jul 26, 2015 at 17:47
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    $\begingroup$ @WernerCD I won't argue this with you, but try playing some Kerbal Space Program and you'll quickly see what I mean. You can simply fall from space, but you can't fall from orbit. See also this article. $\endgroup$
    – Thane Brimhall
    Jul 26, 2015 at 17:52
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Physics makes it impossible even with a superhuman hero and matching fishing line composed of perfect carbon nanotube (CNT).

At geosynchronous orbit (GEO), our hero is moving at 3.07 km/s To make a perfect straight down cast our hero would have to actually drop its orbital velocity to zero horizontally plus whatever vertical component he can manage. Momentum conservation just changed our hero's orbit, he is no longer in GEO as required for an orbital fishing platform. Because even the perfect CNT line 35800 km long has a significant mass, the orbital change will be correspondingly large.

Now our hero is also smart and realizes he needs to compensate for the orbital change and casts a second ballast line in the opposite direction the same time to stay in GEO.

When the line finally hit the atmosphere, the atmosphere will be traveling at about 465 m/s (equatorial velocity) -- it just became impossible to hit any target. Wind drag will quickly accelerate the bait end of the line to 465 m/s. From this time on, the line is also pulling our hero out of GEO.

Even worse, the ballast line is running out of line at about the same time. It just became a uncontrolled space tether that will also pull him out of GEO. The ballast line will also rebound and jerk our hero out of GEO. Cutting the ballast line just before rebound eliminates this, so our hero needs very keen eyesight or impeccable timing to cut the ballast line. However, without the ballast line we also get pulled out of GEO, just as if he never cast the ballast line in the first place. Definite problem for GEO in either case.

Meanwhile, back in the upper atmosphere our bait is now falling at terminal velocity which is dead slow compared to GEO (actually slower due to the increasing tension in the line). This means the fishing line will spend a lot of time pulling him out of GEO, and our heroes orbit will be pretty far out of GEO by then. Too hard to guess what terminal velocity will be, but the terminal velocity of the CNT line itself would be very low. I would expect the descent time spent in atmosphere would be hours long, if not days long (like dropping a feather).

Somehow, defying all odds, the hook is set. Since you cannot feel the other end of the line, you know this because of your keen eyesight (0.14 seconds later due to the speed of light) and you start to reel in your catch.

So close, but you discover that pulling on the line does not result in a pull at the other end. Turns out that the speed of sound is a limiting factor, the line pull cannot propagate faster than the speed of sound -- perhaps 20km/s. So, setting the hook takes 1790 seconds or 29.83 minutes, your fish is long gone before your jerk on the line reaches the other end.

No fish for you.

Thanks to Hagen von Eitzen for the quick explanation of speed of sound dependency for setting the hook. Perhaps the following explanation will help too. If you stroke a hammer on a railroad line, the speed a sound in steel is how fast the sound propagates through the rail line. But what is sound? It is a compression wave. I.e., the speed of sound in a material is how fast a compression or tension wave propagates through the material.

To be honest, I had forgotten to reflect that the speed of sound in a solid changes with temperature and pressure, but I don't know how to compute the net effect, as I don't know how the density and modulus of elasticity of a CNT will change in the cold vacuum of space. For comparison diamond and quartz have much lower density changes due to temperature than do common metals. So I expect a similar low change in a CNT. So, I expect the overall change is small, even given the extreme cold in space. Perhaps the time required to set the hook is off by as much as a minute or two.

Also admission of dumb mistake. Originally used 42,000 km line, should have used 35,800 km line as you only have the reach the surface of the earth, not the center of the earth - I adjusted my answer.

I wanted to know just how heavy the fishing line would be. On the space elevator blog there is a space elevator spreadsheet. Appears thorough, did not try to check any of the formulas, etc.

If you want to double the end load, double the total weight of the fishing line/ space elevator. 130 GPa is very optimistic for a real world CNT (I did say perfect in my answer), a real measured CNT maxes at at 63 GPa . A safety factor of 2 is really not enough in my opinion for a space elevator (crashing to earth after a break would be very bad), but it is probably ok for a fishing line. A safety factor of 2 means that the is designed to be twice as strong everywhere as the theoretical minimum value. A safety factor of 1.0 means theoretical minimum everywhere (no safety factor)

  • Strength: 130 GPa, Safety Factor: 1.0, Load: 10kg, Line mass 147 kg
  • Strength: 130 GPa, Safety Factor: 1.5, Load: 10kg, Line mass 271 kg
  • Strength: 130 GPa, Safety Factor: 2, Load: 10kg, Line mass 444 kg
  • Strength: 130 GPa, Safety Factor: 2.5, Load: 10kg, Line mass 683 kg
  • Strength: 130 GPa, Safety Factor: 3., Load: 10kg, Line mass 1010 kg

Or more realistically

  • Strength: 63 GPa, Safety Factor: 1.0, Load: 10kg, Line mass 470 kg
  • Strength: 63 GPa, Safety Factor: 1.5, Load: 10kg, Line mass 1084 kg
  • Strength: 63 GPa, Safety Factor: 2, Load: 10kg, Line mass 2228 kg
  • Strength: 63 GPa, Safety Factor: 2.5, Load: 10kg, Line mass 4300 kg
  • Strength: 63 GPa, Safety Factor: 3., Load: 10kg, Line mass 7985 kg

Also in the real world you have other problems that I have neglected.

  • On entering the atmosphere your line would burst into flames and disappear
  • I've neglected to mention that your platform continues in GEO while your line is descending. You need to throw it very fast indeed to reduce this problem
  • Casting a fishing line works because the plumb is much heavier than the line so the line follows the plumb. We have something that cannot actually be cast
  • The line is an incredible safety hazard. The end diameter is so small, you would not be able to see it and would probably slice off body parts trying to attach the hook
  • Who fails to pack lunch for space but brings along a tiny space elevator just in case?

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      $\begingroup$ Nice point on the speed of sound! Maybe we can poison the hook, or replace it with a bear trap. $\endgroup$
      – Kristján
      Jul 26, 2015 at 16:08
    • $\begingroup$ Why the speed of sound? The speed of sound is a good limit for a wave (say, the fish moves horizontally and that vibration is transmited) but if the astronaut recovers the line (assuming it is perfectly tight and no wind) I would expect the effect would be felt at C. Otherwise, if he has a 20000 km line and is recovering 100m/s, for 100 seconds the far end does not move making the line effectively 20010 km long. $\endgroup$
      – SJuan76
      Jul 26, 2015 at 16:18
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      $\begingroup$ @SJuan76 Pulling the line propagates by the intramolecular forces of the line. i.e., a decompression travels along the line - which is nothing else but a sound wave. In your example, yes, the line might become a lot olonger per elasticity - or it might become very difficult to keep pulling. $\endgroup$
      – Hagen von Eitzen
      Jul 26, 2015 at 16:49
    • $\begingroup$ This is the only physically accurate answer as far as I can tell. Orbital physics make it REALLY hard to even cast the line. $\endgroup$
      – Thane Brimhall
      Jul 26, 2015 at 17:48
    • $\begingroup$ I like the idea of fishing with a bear trap. That will significantly increase terminal velocity too. $\endgroup$
      – Josiah
      Jul 27, 2015 at 14:59
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    With regard to accuracy, it's completely impractical.

    1. You haven't stated what orbit he is in. If it is not geostationary then it will end up dragging over sea and land.

    2. If he is in geostationary orbit then he must be above the equator. You can't have a geostationary orbit above the poles.

    3. If he is above the equator, he has a real problem. The line has to be ultra light-weight. Unfortunately this means it can easily be blown around by air currents as he lowers it. At the equator the air flow at the upper layers of the atmosphere diverges towards the poles. The fishing line might never touch water or, if it did, the place would be very difficult to predict.

    enter image description here

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    • $\begingroup$ I suppose that if we count the wind, if he wants to fish in the Pacific, he needs to release to rope from the other side of the Earth. (The math is not right, but you get the idea) $\endgroup$
      – Ooker
      Jul 26, 2015 at 16:25
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    If the cable is made of "string"(string theory) it would be even able to touch (wihtout getting any fish, the fish weight would break it) the surface of a black hole, but since in reality materials are much more weak it could still be viable doing that in example on earth,

    the key is to find a cable strong enough to sustain its own weight (when you have kilometers of cable it starts to be much heavy).

    You will be surprised by how many materials would allow fishing from orbit.

    A steel cable would break under its own weight at a lenght of approximately 25 kilometers (it is a strong material, but also a heavy one, and so is not appropriate for "fishing operations")

    spider silk looks like a much more valid alternative (you can do a spider silk cable long up to 109 km, yes a natural material beats by an order of magnitude a man made material).

    However the most promising material for doing that is colossal carbon nanotube with over 6000 km of avaialable lenght (before breaking under its weight).

    All the above numbers are taken from wikipedia

    However there's a pitfall, I assumed the rope would be the same diameter,

    in reality you could engineer a rope wich is thickier at greatest height, that would require much more material, but also allow to create a longer "rope" (I'm not sure to call rope something that has not the same diameter along the whole lenght). Doing that would allow to fish from very big distances, until you touch other physical limits (if your rope has the mass of a star or of a black hole it will collapse and have its own gravity field, by the way a body with a strong enough gravity orbiting around Earth is going to take out of the surface the water and all fish it contains without the need for a rope).

    Using another engineering approach is to reduce the "fishing rod problem" to the "space elevator". As noted in the comment, if space elevator is possible, then it is also possible a "space fishing rod", and seems there's already people planning to build a space elevator:

    Space elevator is possible so it is space fishing rod.

    So fish for you is possible ;).

    EDIT: I wanted to note that on worldbuilding there's much discussion among "experts" that both claim such thing is not possible or claiming the exact opposite. I believe it is possible (different from claiming it is possible), and materials are already present, we just need "logistic effort". I've also read on papers that is theorically feasible (also on LeScienze, wich is the italian version of "Scientific American")

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      $\begingroup$ On worldbuilding there is much discussion about orbital elevator, if orbital elevator is possible, then also fishind rod is possible. Materials already exists, but there may exist also other reasons that make such creation unviable. $\endgroup$
      – CoffeDeveloper
      Jul 26, 2015 at 10:03
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    There is a way, but it bends the idea of "casting" and "line" into a taffy like mess.

    Hans Moravec is credited with developing a variation of a space elevator called a "Rotovator". Essentially it is a satellite who's centre of mass is in LEO, but has two equal extensions the rotate around the centre of mass much like spokes on a bicycle wheel. One end at a time will plunge into the atmosphere in order to hook on to cargo, then lift it up into orbit and release it at the top of the cycle, ejecting it into a high orbit. To maintain momentum, the rotovator can also accept incoming cargo from high orbit and drop it to Earth.

    Rotovators can come in all sizes, from "short" rotators which pick up cargo from hypersonic aircraft or even low altitude rocket vehicles in the upper atmosphere to truly titanic devices which can (briefly) touch down on the surface and pick up cargo from a cargo facility. This would be like a combination of air to air refuelling and a "touch and go" runway landing by a supersonic jet, so the cargo pod would need to be rugged and carefully aligned before the Rotovator comes overhead.

    You can read his paper here: http://www.frc.ri.cmu.edu/~hpm/proje...ers/scable.pox

    And a somewhat fun YouTube video that explains the concept visually: https://www.youtube.com/watch?v=Z81wpmqXQLo

    For fishing, if the Rotovator can be aligned to come down over a stretch of ocean which is already identified as having a large school of tuna or equally large game fish, and the intrepid fisherman is clinging to the end with his trusty spear gun, and is getting real time intelligence as to the location of the fish (perhaps by using the sniperscope from the previous question) and the gods of fishing are all smiling that day, he might be able to spear a tuna at the moment the rotator arm touches down on the surface of the ocean, and bring it back into orbit for a fish fry.

    Maybe.....

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      $\begingroup$ I thought about a rotovator myself, but thought it was a bit of a stretch for the definition of fishing rod. It did not occur to have the have the angler stationed on the end of a rotovator line. If you can do this though, have the angler jump off go fishing, etc. the catch another line when he want to return to space. $\endgroup$
      – Gary Walker
      Jul 26, 2015 at 19:14
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    One issue with fishing from orbit is the massive pressure difference between orbit and the sea. Even disregarding the pressure of the water itself, the pressure of the air is about 14 PSI. Any gases and fluids in internal organs would swell up immensely, and any free gases in the bloodstream would form air pockets. it's even possible that the fish might explode, similar to how deep sea fish sometimes explode when surfaced too quickly.

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      $\begingroup$ The common trope re: people (or fish) exploding in vacuum is simply not true. NASA accidentally performed this experiment on a person, did not even kill hum. Deep water fish have a much greater pressure change when lifted to surface pressure than a surface fish exposed to vacuum. Sure the fish will die, but it should still be edible (once warmed up). The visual presentation of the meal might be less than optimal though. $\endgroup$
      – Gary Walker
      Jul 26, 2015 at 19:09
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      $\begingroup$ @GaryWalker Humans may not explode from being in a vacuum, but I can't find anything about live fish doing the same. Apparently, noone has considered yet to put a live fish inside a vacuum. $\endgroup$
      – Nzall
      Jul 26, 2015 at 21:39
    • $\begingroup$ Well, since humans and fish are basically composed of basically the same material you would expect similar results. Actually, I expect fish to do slightly better since they don't have any lungs to rupture if they make the mistake of trying to hold their breath. You may die quickly due to a heart attack, etc. They have done studies on strength of cell walls (plant and animal) and the tensile strengths of individual cells are typically 20-100 atmospheres. NASA animals studies are at ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660005052.pdf. Mostly dogs, but some spider monkeys. $\endgroup$
      – Gary Walker
      Jul 26, 2015 at 23:28
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    problem 1: The fishing line snaps under it's own weight because it is longer than indended by the manufacture.

    He then goes and gets a thicker gauge of line. This leads to problem 2.

    Problem 2: The weight of the line pulls the satellite out of orbit. If this were not the case, then he would have won a Nobel prize for creating the first space elevator.

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    The fish will long be gone if a hook system is used. A better solution would be actually using a cage/container which the fish cannot leave, with a bait placed inside it. The container should be sealed and pressurized so that the fish won't explode due to vacuum and could possibly survive until arriving in geostationary orbit to be cooked and eaten.

    The fisher will need a spaceship capable of neutralizing the forces that are enacted on it when the fishing module enters the atmosphere. The fishing module will have to be outfitted with a heatshield and a parachute, of course. The string will probably be carbon nanotube stuff.

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