This is the sort of thing I would ask @nyrath about. I don't know if a mention like that can summon him.

I love to think of fanciful physics for astronautics, and I think audiences like it best when the system is self-consistent. It's very hard to design systems that don't lead to contradictions or paradoxes. In a way I think it's like designing a playable game.

My mind immediately went to an as-yet unexplained "inertia sink." My idea is that it somehow (space magic) robs the target of all of its momentum to stop it dead, perhaps channeling it back to the aggressor or into an explosion to knock out the target's engines. Dunno how or if it would work in your universe, though.

IDK if anticlimactic is the right word. If the antagonists know where the protagonists are going, why would they go out of their way to interdict? Just go where they're going to be and kill them on arrival.

Alternatively, what if the antagonists just have a spy/traitor onboard the heroes' ship?

Just hit 'em with an EMP. Your ship isn't going anywhere while unpowered, even the jump drive will have a "spooling up" period that can be interrupted, and even the most basic, disposable form of thrust - being a solid fuel rocket - can't be fired without a spark. You either have an electronic starter, disabled by the EMP, or else someone crawls up the exhaust tube with a Bic lighter and sacrifices every component atom of their existence to the gods of fiery speed.

The game Starsector has a neat play on this, where certain ships can fire off an "interdiction pulse" which is a short range directed EMP that shuts down the engines of whoever it is pointed at. You can outrun it with a good heading and good tactics, you can juke it with careful positioning, or you can go dark and camp in an asteroid belt and hope the space cops miss you on their search. But if you get got by the interdiction pulse you've got a good 60 seconds or more of being a sitting duck in space. No engines, no comms, you're lucky if the life support even keeps pumping oxygen while the corvettes close in.

If you don't want to deal with the plot holes that massive EMP bursts bring (how do you shield your ship against it's own EMPs? How do you pierce a shielded ship with one?) you could make an "interdiction module" be a legally mandated piece of equipment in every ship, which when activated, cuts power to all major systems. Sort of like how ID transponders are usually handled in space operas - hell, combine the two together. Any ship running dark without a transponder active can be considered a threat to be removed on sight, not only because they aren't broadcasting an identity but also because they may not have an interdiction module installed. Skip the pulling over part of the traffic stop and step right to torpedoes, because they are probably pirates.

Naturally, real pirates won't have an interdiction module and will be attacked on sight by most security forces. A hypothetical protagonist would be able to sabotage their own module to escape capture, at the cost of being assumed to be a pirate until getting it fixed or replaced at, more than likely, a less-than-reputable shipyard.

Ooh - workshopping a scifi story? My time to shine!

1. Check out how the Star Wars EU handled this in the Thrawn series (Hint: Interdictor cruisers)
2. Tractor beams - your friend and mine
3. Think of every way other people have done this and ask yourself - "how could it be different?"
4. Plausible is fun but pleasure is better - people need a story they can engage with and will forgive all kinds of logical fallacies if you've engaged with their emotions sufficiently.

Hope that helps

Source: I do this for a living

As someone who has to write RPG settings and scenarios, if I can't be consistent with the tech or magic, then I think of what would be the easiest way to do something.

In this case? If I had to do this and didn't want to throw in crazy tech? Easiest way to stop the Heroes? The Villains bribe/blackmail someone to interrupt the jump, or they've planted a device to sabotage the engines at a certain time. They're waiting at that point.

Nothing like a good ambush AND some intrigue ("how did they do that?")

My players hate when I interrupt their journey. We're on month 3 of adventures due to an interrupted journey... and now they trust NOBODY!

You can take an idea from real life(very sad news though when I heard).

The MagLev trains run very fast through a predetermined route. Technically they can go really really fast. But they have to run through a pre-determined route. However, it is through a series of magnets. Earlier iirc, there was a train when some evil people removed just a single magnet and caused the train to crash.

In your novel, the heroes are taking the predetermined route. The main challenge for agents should be to figure out the route. Then pay some mercenaries along a route which cannot be well monitored (due to being remote or conflict zone) to sabotage the route. As the route is predetermined, exact position of the vessel at exact time is known in an unmonitored area. This can be used to create a simpler electromagnetic trap which would reduce the speed over a long distance, or divert the route. EMP can be used to disable the ship, making the ship just a container being transported. The trap later being destroyed, but still leading a trail behind for someone to find what happened. This should work as long as speed is less than light, should work for <0.5c. But the area of influence where control is not possible should be a large geograhic area due to speed.

You can also have that at that particular spot the speed is slow due to a curve etc. And villians are just removing what is causing the route to bend for just an exact moment when heroes are travelling there.

You said there is near-instantaneous communication. How about having the agents "phone ahead" to another group of agents that are nearer to the place the heroes are going and have them jump there first, so that the heroes arrive into an ambush? Police do that sort of thing in high-speed chases in the real world.

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Maybe something where the well generator pulls your Heroes off course from the pre-defined trajectory and they "drop out" to an unexpected situation, like (and also unlike) when the Millenium Falcon arrives at "Alderaan"?

I guess the method you choose depends on your universe's departures from "real" physics, but also your story's narrative aims. Are you looking to build a tense chase sequence or have a gotcha surprise?

0.5c? Is this all taking place in one solar system?

Not directly related, but .5c is going to be slooooooooooow for interstellar travel. Proxima Centauri is roughly 268,770 AU away, and 1 AU is about 8.3 light-minutes. That works out to be 2.23M light minutes, or 4.2 light years. If someone is traveling at .5c, that's 8.4 years to get from our solar system to the very closest star system. And of course it's all at relativistic speeds, so while it may not feel long to the people on the ship, it's still the better part of a decade.

Right now, the closest earth-like planet we know of (similar size, similar star, similar orbital period) is Kepler-452b. Kepler-452b is 1800 light years away, or 3200 years for the people observing the craft that was traveling there. This is getting solidly into Joel Haldeman's "The Forever War" territory.

IMO, unless you want to do a lot of math to figure out the effects of time dilation, you might want to have some kind of science-magic that allows your characters to sidestep relativity.

(I believe it was Charles Stross that worked relativity into a galactic cryptocurrency economic system. He got around relativity by assuming that almost all people were inorganic, and able to copy and back up their consciousness, or sleep through the decades that interstellar travel required.)