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So I have a bunch of space pirates who make a living out of stealing spaceships while they are in transit and repurposing then for their own use later. As such, they can’t destroy the ship because, well then the ship would be destroyed and thus unusable. These pirates also have lower tech than the other major players in the galaxy so they don’t have fancy “disable the vessel” energy blasts. So they’ve come up with a very effective strategy.

They come out of hyperspace near their victim and attack their engines with lots of small kinetic projectiles and lasers until the vessel is largely immobile. They then fire their harpoons, which are missiles with thermite warheads that burn though the outer layers of the hull. Several spikes extend from the body of the harpoon, anchoring it to the ship, and a cable extends from the harpoon to the firing ship. Usually multiple ships harpoon the victim and then tow it back to base.

I have a bit of a problem through. Metal cables don’t really seem like they would be strong enough to handle the stresses that would be involved in this situation, so I need a more believable way to anchor the victim to the pirate vessel. Is there some type of alloy or super material that could withstand the stress better, or is it better to just use more harpoons to minimize the stress on an individual? Bonus points for a better harpoon mechanism in general, as the best I could think of was burning into the hull.


marked as duplicate by kingledion, sphennings, Renan, Anketam, John Jan 31 '18 at 22:49

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    $\begingroup$ I'm sure a question like this has been asked before... $\endgroup$ – F1Krazy Jan 31 '18 at 16:45
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    $\begingroup$ I hear handwavium makes excellent space harpoons. $\endgroup$ – sphennings Jan 31 '18 at 16:49
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    $\begingroup$ Ah handwavium, the most versatile, useful, and tasty of all fictional materials. $\endgroup$ – Nick Jan 31 '18 at 16:50
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    $\begingroup$ Check out Firefly / Serenity - watch the reavers in action. $\endgroup$ – pojo-guy Jan 31 '18 at 16:52
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    $\begingroup$ I was thinking that as the pirate ship accelerates there will be stress on the cables until the victim ship reaches the same speed, as they are connected by flexible cables instead of solid struts. However, dental floss pirates..... I like it. $\endgroup$ – Nick Jan 31 '18 at 17:09

I think you've mixed your metaphors....

Ships are not whales. Harpoons did not drag a whale any significant distance, actually the opposite: a harpooned whale dragged a small boat with the harpoon men aboard (called a sleigh ride) until it gave up from exhaustion and floated on the surface, vulnerable. The whaling ship caught up with them and processed the dead or dying whale on the ship before dumping the carcass at sea. Harpoons aren't tow lines for large heavy objects. The problem isn't rope strength, the whale's flesh (and by metaphor your ship hull) would tear apart where the harpoon had penetrated long before the rope broke.

Piracy does not mean dragging a ship back to base, that only makes sense if the ship is salvage and has no power. Your pirates are sitting ducks while acting as a tow truck, not just from a space navy but from other pirates.

Piracy generally means one of two things: capturing a ship to steal it, or (more often) temporarily disabling a ship to board it for loot and taking any passengers who could be ransomed.

In reality, intercepting and boarding another ship would be impossible at interstellar speeds without catastrophic impact, so ignoring that small technical issue we still have two main strategies:

  1. Capture the ship with a boarding party and re-route it under its own power (this almost never happened).
  2. Compromise the ship's ability to reach its destination forcing the crew to surrender or lighten the load by dumping cargo.

The first strategy is likely to get many of both crews killed, and it's possible the prey's crew will destroy their ship if the battle is not going well and they assume they will be killed anyway. The pirates also need TWO complete crews – maybe not a big deal if their prey is a small yacht, but another large ship needs experienced crewmates. Back in the buccaneer days, common sailors were so badly treated that it wasn't difficult to get them to join the pirates when given the option to mutiny, in fact many pirates were former navy. Still, this is the least likely of the strategies to be successful, and certainly the most dangerous for the pirates.

The second strategy might be as simple as driving the ship off course, or forcing them to burn fuel to stay out of gun range until they no longer have enough fuel or forward momentum to get to their destination. Every course correction would be a drain, until it is easier to give the pirates what they want (money, cargo, wealthy passengers) to let them go free: the equivalent of cooperating with highway robbers.

You pirates aren't going to defeat anyone with damaged ships. They already have lower technology and resources. They might be better off stealing money and ransoming aristocrats to BUY a working used ship, than attempting to repair a ship they'd already almost destroyed.

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    $\begingroup$ "[...]but from other pirates"...and from any still-surviving, very pissed-off crewmembers of the prize vessel. $\endgroup$ – mikołak Feb 1 '18 at 8:48
  1. Shanghai!
    /Usually multiple ships harpoon the victim and then tow it back to base./ You got there thru hyperspace. It is a long walk back. Do they bring the captured ship back thru hyperspace? I am sure they do not pull it along on a leash. Have your pirates show up around the ship and whisk it away in a hyperspace bubble without a shot fired. The prey ship comes out of hyperspace at the pirate lair and a robot arm severs the engine a split second later. Less damage to ship, you can sell the engine too, and you can ransom the crew. Everyone is happy!

  2. Cnidocytes. The hydra is an animal which captures prey with tentacles. Some are harpoonlike and sting. But other are long, wrapping around and entangling the prey. http://bodell.mtchs.org/OnlineBio/BIOCD/text/chapter23/concept23.3.html hydra tentacles

. Tubules of some cnidarian species have barbed ends, while tubules from other species are sticky and wrap around the prey.

Your gooey "harpoons" could wrap around and entangle the ship. Resale price is higher without all those railgun holes in the hull. Also tenacious harpoon goo would be useful for pirate pranks.

3. Screw you Your customers do not like the effect thermite has on the reflective finish of the high end ships you capture. The screw harpoons have sharp diamond tips, and the harpoons are spun up very fast before launch. On hitting the target their rotation screws them securely into the hull. The spin also gyroscopically stabilizes them in flight which is a nice byproduct.

4. Tugbots.

Tugbots https://www.youtube.com/watch?v=0_kMhMHRAQE

This is from The Expanse - hundreds of these little tugbots fly out, clamp on the ship and fire up. More precise than tying the ship to yours like some overgrown waterskiier. You could have tugbotpoons that approach more aggressively but do the same sort of thing.


Synthetic spider silk might do the trick. Spider silk is one of the strongest materials we know about, with a tensile strength on par with Kevlar, but a much higher material toughness. Both of these exceed steel by a large margin. Woven into a rope, you would have a very strong, elastic material that is highly resistant to breaking.

In terms of an overall harpoon system, thermite can be tricky for a number of reasons, most of which involve contaminants in the mixture that can cause the reaction to spray molten metal everywhere. A thermite harpoon hitting the wrong spot might destroy your target (depending on how they're generating atmosphere inside the target).

In lieu of a harpoon, you might just use a big spider-silk net towed by multiple ships. That way you don't have to puncture the pressurized metal air canister that a spaceship functionally is (while introducing the heat from a thermite reaction to the suddenly-out-rushing air).

If you like the visual implications of a harpoon, you might not need the thermite at all. Use a railgun to accelerate your harpoon to very high speeds. If energy weapons/defenses are normal in your universe, ships may not be relying much on thick protective armor for protection. The kinetic energy of the harpoon, along with a sufficiently strong/hard material, may be enough to puncture the ship's hull. Include a spring-loaded mechanism that pushes the grappling fins into place when either the line begins to be retracted or the forward inertia of the harpoon drops.


There are a bunch of synthetics that you could use. A popular one is Spectra


You could also use carbon fiber.

The stresses might not be very high, though. if the ships are matching direction & velocity, the most stress you could put on the line would be the maximum thrust of both ships. Considering that space ships are probably built to be light, and if they accelerate too fast, they knock out their crews, it might not be as much as you think.


Rather than having stronger cables, maybe the cables could just be power and data lines, with the head of the harpoon breaching the hull of the target ship, before interfacing with the internal network. Could be a race to take control of the ships propulsion systems and navigate the ship remotely, before the maximum length of the cable is reached and severed.

Usually multiple ships harpoon the victim and then tow it back to base

Redundancy, perhaps the crew on the target ship would work to disconnect the harpoons, thus the pirates use multiple to increase their chances of success.


Lets get some Maths done - how many cables do you need?

Unless your pirates have handwavium inertial dampeners, they will likely limit their engines (outside of combat or emergencies) such that acceleration is about 3 gees (i.e. 3*9.8 meters per second per second)

30 m/s/s acceleration, towing an enemy ship of mass M kg. So the total force required is 30*M (kg m/s/s).

This can be expressed as 30*M Newtons (N)

A 36 mm thick normal steel cable has a maximum rated tensile strength of 1000 kN. That's not to say it will definitely break at 1001, just that it definitely won't break at 1000.

So the number of cables we need (N) is N = 30*M/1,000,000.

For the international space station, M = 420,000.

N = 12.6, but we should round UP in all cases, so 13.

Note this will require the pirates to be moving extremely slowly when the cables go taut, make sure all 13 cables are sharing the weight equally, and THEN accelerate.

This number could be reduced by having thicker cables. Each spaceship could use multiple harpoons, or you could have some material better than plain old steel.


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