# A weapon(preferably hard scifi) that will limit velocity of space ships in a wide region temporarily

Ships are capable of FTL warp and relativistic speed flying. In order for a ship to intercept other ship at high non-FTL speed, it needs a mechanism that will enable it to slow down the other ship.

Most space battles will ensue after the speed-limit weapon is deployed, creating a region of space where ships are experiencing drag and will make them harder to escape and accelerate virtually to speed of light.

Things I'm looking for:

1. A missile payload that will disperse high friction gas that have will linger in the area(fast initial dispersion, but slows down eventually).
2. A device that increases the relativistic effect, so less acceleration due to increased mass when traveling at high velocity.

Things I'm NOT looking for:

1. Gravity tether or tractor beams. It needs to be an area of effect, causing multiple ships to slow down.

UPDATE: Thank you for all your contributions!

To clarify, the weapon is not to disable FTL warp, as in my setting, it requires substantial preparation to make an FTL journey, so no emergency jump.

The weapon is needed to keep ships from accelerating constantly achieving relativistic speed and escaping. Otherwise, there will be no practical way to catch smaller faster accelerating ships. Also, I didn't want the space battle happen at lower velocities, somewhere between real space battle and atmospheric dog fight.

• Suddenly applying friction to something moving at high speed is likely to obliterate it outright. Also, the area of space you'd have to cover is likely to be ridiculously large, to the point of you'd have to convert a small planet into gas to have a meaningful effect. – Erik Apr 18 '17 at 13:13
• A hard sci-fi "gravity tether" would be area of effect (really just a gravity well). I think manipulating space time curvature is probably you best bet (rather than locally lowering the speed of light, as you seem to be suggesting) – ApproachingDarknessFish Apr 18 '17 at 13:42
• The word - I have 10 FTL torpedoes, first 10 who will try to escape will have those torpedoes on their back. Good luck trying. – MolbOrg Apr 18 '17 at 15:34
• You'll have to explain how your FTL works before we can figure out how to disable it (unless the answers get to make that part up, too?) – Schwern Apr 19 '17 at 0:06
• @James How? This is space. Without friction, a spacecraft disabled by EMP will keep going at the same velocity. – Brian McCutchon Apr 19 '17 at 3:45

The only answer I can think of that doesn't require warping the laws of physics or a ridiculously huge energy budget is:

Tugmines

Basically ridiculously powerful engines fastened to mildly ridiculously powerful magnetic clamps. Unmanned, a Tugmine will seek out, match velocity with and fasten onto any ship not broadcasting the correct IFF (or, if electronic warfare is a factor, any ship, to avoid potential hacking/spoofing attempts), clamp on and then use internal accelerometers to oppose the acceleration of the vessel and return to their original velocity. This should reduce other vessels to the velocity of your cloud of mines, and has the advantage of moving any scrap metal back into an easily harvestable location.

Naturally a single Tugmine won't be able to outpower an entire enemy vessel, but a series of them will at least make them less able to accelerate and manoeuvre effectively, while the small size, high power and unmanned nature of the mines will let them catch up with and swarm enemy vessels. Depending on how sophisticated the mines are you can also build in countermeasures (exploding) to prevent their removal, have them track coverage of enemy vessels to provide the most efficient opposition, or have specialist mines that aim for and destroy enemy engines.

Fighting in a cloud of mines seems like a pretty daft way to fight though, so unless your aim is specifically capturing enemy vessels you'd be better off just strapping explosives to the tug mines and using them as long range missiles. Vessels with squishy meat bags in them won't be able to out accelerate unmanned murderdrones.

A quick note This is assuming that fuel isn't really an issue. This becomes a whole different question if you're taking the tyranny of the rocket equation into account.

• You can mine a harbour to block ships from going out or even a beach to prevent disembarking, but you can't mine an ocean. Much less the outer space. Even with mobile, self-guided mines, the amount of space to defend makes it impractical, and in any case mines are always deployed in advance, it's not a thing you can deploy as the first action of a starting battle. – Rekesoft Apr 18 '17 at 14:45
• @Rekesoft Yep, space is huge. Which always wrecks my suspension of disbelief whenever I see a "planetary blockade" of like 10 space ships. You'd need tens of thousands, at least, even if you only had to worry about major population centers. – TylerH Apr 18 '17 at 15:07
• Ignoring the rocket equation is a massive handwave. – sphennings Apr 18 '17 at 15:38
• @sphennings: The OP states that his ships can get to relativistic speeds. Doing that without having a decently long run-up requires some massive handwaving anyway. – Joe Bloggs Apr 18 '17 at 15:41
• If you can attach a tugmine to an enemy ship, what prevents you from making the tugmine attach a nuclear bomb to the enemy ship and then disengage? Why would you slow them down and then fight? – sampathsris Apr 19 '17 at 4:49

In hard sci-fi we have nothing - since we don't have FTL or anything approaching it then it's impossible to do anything beyond pure speculation in terms of anti-FTL.

My suggestion would be some sort of warp or distortion field that you apply over an area. It distorts the space within the field in a way that interferes with drives, or maybe even with the structure of ships itself.

Think of it as being like ruts and bumps in the ground. You slow down to go over them since otherwise you might damage your vehicle. Do that to space :)

• Are tidal effects worse at relativistic speeds? Could make for a suitable 'speed bump'. – Joe Bloggs Apr 18 '17 at 14:12
• Any kind of wavy potential difference will cause a degree of damage that depends heavily on the structure of the ship passing through. In general though, higher frequencies have a higher potential for forming resonances, and higher approach speeds Doppler shift the frequencies up, so slowing down would be an appropriate response to an incoming oscillating field which affects the ship structure. – Asher Apr 18 '17 at 17:34
• I would imagine any FTL device would require specific, moderately ideal conditions to work correctly, found commonly everywhere except maybe sharp gravity wells. An EMP like device for Space-Time that destabilizes it for a while could, within suspension of disbelief, make it unsafe to initiate FTL. Like trying to launch a Rocket into space, during a heavy storm. I would imagine it being incredibly difficult do any space-time related FTL even normally, and if space time is rippling like disturbed water, the waves would act like moving speedbumps. – Ryan Apr 18 '17 at 18:47
• @Asher: Or building your ship with active space-time wave damping in mind. Similar to building skyscrapers to avoid resonance issues, only moving at mega metres per second. And in space. – Joe Bloggs Apr 18 '17 at 21:39
• Stasis webifier anyone? – Zimano Apr 19 '17 at 7:15

## Chaff

Since few spaceships are likely to be steered manually, chances are they've got instruments and RADAR/LIDAR style sensors so they can tell what speed it is safe to fly at. At high speeds, even simply dust can cause major damage (or drain shields / power etc) - so these automatic instruments adjust the speed to try and reduce the possibility of damage. Firing a cloud of chaff would simply cause them to reduce their speed as it wouldn't be clear whether it was safe or not.

An added effect could be the chaff itself being metallic and/or magnetic - and effectively fouling up the sensors if the ships don't reduce speed and maybe fire an electron beam to repulse it. This would let the pilots override the sensors, but have to clean up afterwards, or perhaps simply risk collision with something they can't pick up visibly.

If it's a material that reacts with interstellar hydrogen to become "normal" space dust then it would be a sort of self-clearing system.

The natural follow-on would be using it to hide mines and boarding parties from sensors until the area is cleared.

This solution is employed in the book Green Mars by Kim Stanley Robinson. A chaff missile is fired in front of a vessel which is about to aerobrake into Mars orbit. Upon detecting the obstruction, the ship autopilot chooses to avoid the aerobraking manoeuvre (and is thus unable to enter orbit) rather than risk flying below the 'obstruction' and burning up in the atmosphere.

The point is that spacecraft manoeuvres tend to take place in a narrow envelope of possibilities determined by the physical reality of their propulsion systems and environment. When a spacecraft is near the edge of it's permitted manoeuvre envelope, dramatic changes can be leveraged by small adjustments (such as shifting a velocity vector by a few degrees to avoid a chaff cloud).

If your FTL drive requires some sort of very accurate manoeuvring, then you might not require major disruption to the spacecraft to render the jump impossible.

• I think fooling the sensors is the most straight forward solution. You wouldn't dive straight into an area in which you have no idea what lies beyond (maybe it's an asteroid field). – Deruijter Apr 19 '17 at 9:13

How about sand bombs? Containers full of fine particles that spread out into dust in an area of space. They would continue to disperse, so the effect would be temporary, but for a limited duration, there would be a fairly large amount of particles in space that might bounce off the hull of a ship.

I have to imagine what the transition from high relativistic velocity to FTL would be, but presuming it was some kind of continuation of acceleration, we can guess that a ship might have means of handling particles in space at specific speeds, but that the acceleration to FTL would be beyond the capacity of the armor, magnetic fields, or whatever else they are using to protect themselves from a particle bouncing off the hull.

Some points to consider: The sand bomb could not merely fly past the target and go "pop". It would have to accelerate past the target, then significantly accelerate back toward the target, so the cloud of "sand" (dust) is moving SIGNIFICANTLY slower (relatively speaking) than the target. Sort of like a boomerang missile trajectory. This would require the expenditure of a lot of energy for acceleration. The bigger the gap between the relative speed of the sand bomb dust cloud and the target, the bigger the fuel expenditure of the missile to accelerate and the smaller the payload you can reasonably expect to carry.

Other things to consider: It's very likely that if there were some kind of accelerating transition from high relativistic speeds to FTL, it would take place in a VERY "empty" part of space. Even a single grain of sand hit by a ship going at high relativistic speeds could cause massive damage (they would have to have some means of dealing with this). The "sand bomb" couldn't do that much damage unless it was able to get so far ahead of the target and accelerate so much in the opposite direction that it was essentially at relative "zero" velocity (whatever that means in deep space) relative to the target ship. That would require a truly VAST amount of energy, and a bit of time, so it's very unlikely.

• Space, contrary to its name isn't empty. Your sand is already there. – Aron Apr 19 '17 at 23:40
• @Aron, what is "there" depends VERY much on exactly where you happen to be. It is assumed that ships moving at high relativistic speeds are NOT going to be doing so in areas of high density. There are large areas of space with virtually nothing whatsoever floating around. – JBiggs Apr 20 '17 at 0:15

Negative mass. You have FTL so the door is open for other spooky entities joining the party.

Negative mass produces a repulsive effect - the opposite of gravity. A cloud of negative mass will produce a repulsive effect on other mass. This will be constant, and the negative mass particles will chase the positive mass of the ship, continuing to repel it - runaway motion. As with gravity, the closer the ship gets to the negative mass particles the stronger this effect will be. From Wikipedia.

Runaway motion

Although no particles are known to have negative mass, physicists (primarily Hermann Bondi in 1957,[2] William B. Bonnor in 1989,[8] then Robert L. Forward[9]) have been able to describe some of the anticipated properties such particles may have...

For two positive masses, nothing changes and there is a gravitational pull on each other causing an attraction. Two negative masses would repel because of their negative inertial masses. For different signs however, there is a push that repels the positive mass from the negative mass, and a pull that attracts the negative mass towards the positive one at the same time.

Hence Bondi pointed out that two objects of equal and opposite mass would produce a constant acceleration of the system towards the positive-mass object,[2] an effect called "runaway motion"

Ultimately the repulsive action of the negative mass on other negative mass will lead to these negative mass pieces breaking up with the indivisible bits taking up residence in space at maximum distance from any other sort of mass.

I think this is cooler and more high SF than space caltrops (not that there is anything wrong with space caltrops!). The math associated with negative mass can allow you to have other high SF fun weirdo effects as well. For example, a piece of negative mass loose in the mess hall.

• The positive mass will chase the negative mass, and two negative masses actually move toward each other - the gravitational response is negative ("repulsive gravity") but the inertia is also negative (so "repulsive" forces actually "attract"). Either way, a nearby negative mass cloud will accelerate a ship, not stop it as the question asks. – Asher Apr 18 '17 at 17:39
• Negative repels negative and positive both. Negative in front of the ship will increasingly repel as ship draws closer. The negative mass will accelerate a ship if you put it behind the ship. Do not do that (unless you want a boost of energy to escape! - see other high SF fun weirdo effects) – Willk Apr 18 '17 at 18:03
• Having just read an article saying scientists created negative mass recently (1 day old article at the time of this comment) although it was just some atoms that behaved like negative mass. Anyway, the stuff has some weird properties. F=ma is just bonkers: give some negative mass a shove and it shoves back. So careful where you fire those things. – Draco18s Apr 18 '17 at 18:19
• @Draco18s Note that there's noöne saying that F=ma would hold for negative mass, if negative mass can exist at all. Just because you can plug a number in an equation doesn't mean that it represents a physical reality. Equations in physics are always a simplified abstraction that has its own (known or unknown) constraints - applying them outside of those constraints is just wrong. We simply don't know if negative mass can exist, and how inertia would behave for negative masses if they do exist. – Luaan Apr 19 '17 at 8:36
• Very true @Luaan. I think of hard sci fi as based on physical laws which are real or logical extrapolations from real physical laws. One could model negative mass, predict how it would act, and make a story around this and similar concepts. This as opposed to supernatural fantasy fiction, where you make up whatever. – Willk Apr 19 '17 at 13:43

In Star Wars they have the Interdictor Cruiser, a ship capable of generating a massive gravity well that makes it impossible for nearby starships to use their Hyperdrives(FTL).

Interdictor cruisers had the same general shape as a Star Destroyer, and were roughly the same size. They featured four gravity well projectors which were employed both to pull vessels out of hyperspace and keep them from making the jump to hyperspace.

This isn't a gravity tether as opposed to a large area-of-effect due to large scale gravity manipulation.

Well if we are talking hard sci-fi travelling at relativistic speed is already incredibly dangerous as even fairly small items (like gas molecules) can be devastating to ship that flies through them so a gas or dust cloud of any sort would be a dangerous obstacle to a ship travelling at 0.9 c or such.

Or, you could just throw a bunch of baseballs into the area: https://what-if.xkcd.com/1/

• Baseballs could damage the spaceship but not slowdown it. – ADS Apr 18 '17 at 20:39
• To be fair, the ship must slow down or be wrecked by bumping into the balls at 0.9c – Vylix Apr 19 '17 at 2:15

Neal Asher in his polity series novels has a device called a USER... an underspace emitter... that makes it impossible to jump into FTL or remain in FTL around the area. Basically it's a singularity (black hole) bouncing in and out of underspace and causing ripples that disrupt FTL travel.

So ships in the vicinity are constrained to sub-light and whatever they can achieve by standard non-FTL drives. So for a society where FTL is the norm and non-FTL is significantly slower than relativistic, you've dropped approach speeds to way under light speed.

• The Polity series is written by Neal Asher not Alastair Reynolds. You may edit your answer appropriately and when that's done this comment will be deleted. You're welcome. – a4android Apr 19 '17 at 8:18

If we are talking science-based, velocity is relative, what is more important is the two bodies velocity to each other, so in your scenario it seems that acceleration may matter more,(prevent the ship from accelerating away, and then match speed so that relative to each other you are at 0)

So an emp field/missile/bomb https://en.wikipedia.org/wiki/Electromagnetic_pulse could accomplish this by taking the other ships electrical systems off line. It would have to be a powerful enough EMP(or specially designed) to overwhelm the inevitable shielding/hardening(shielding in the modern sense eg faraday cage, not a futuristic shield)

• EMP more powerful than cosmic radiation impacting you at high relativistic speeds? That might be quite a challenge, especially if you consider a bomb or a field detonated some distance away from the ship, and at a much slower relativistic velocity... shooting a relativistic spaceship from the back is quite tricky. – Luaan Apr 19 '17 at 8:41
• No doubt, a huge one, but it fits the OP. I also considered suggesting a taser type situation, which also fits, but no matter what it gets REALLY tricky. – theinvisibleduck Apr 20 '17 at 1:43

Possibly something like a high-frequency oscillating warp field ("wobble field") that disrupts "linear" warp field formation and bleeds energy out of existing warp fields, reducing them back into normal space. Probably amplitude would drop off as distance squared though so might need to scatter a set of wobble generators around the area of interest, and obviously ships wishing to escape would target those generators. Also would likely be dangerous to get close to the wobble generators.

I like @joe-blogg's tugmines concept, but if fuel is a concern, I might revisit an old concern: limpet mines. Effectively the same concept, but with an explosive charge attached.

However, rather than simply detonating and destroying the target, you would configure the mine to support remote detonation, or even some small amount of intelligence. Perhaps it uses its physical connectivity to convey an audio warning message:

WARNING! I AM A LIMPET MINE. YOU ARE ACCELERATING AWAY FROM ANCHOR POINT AT ZERO POINT ONE CEE. CEASE ACCELERATION WITHIN 30 SECONDS OR I WILL DETONATE.

Adjust message to taste. Let the mine use high-precision inertics or RF or whatever you like.

If you programmatically think through the mine's sensory analysis and state sequence, you might think of countermeasures, counter-countermeasures, and so forth. Perhaps it resets to 30s after 300s of stillness, in which case a patient target could slowly pulse further and further away. Or perhaps it perceives stillness as anything under 0.1 gee, so a snail could get away. Or perhaps the hull plate it latched onto can be ejected, at a loss of atmosphere and potential risk of detonation.

The payload operation can be different, too, if you don't want to spew navhazard everywhere with a shredded ship. Perhaps it could vent its target's atmosphere. Perhaps it could drill and inject an autonomous drone that'll float/fly around spinning a van de graaf generator, striking random surfaces with sparks; it'll eventually find a critical system to zap.

Or, heck, perhaps it can inject a wad of ignited white phosphorous; that stuff will burn through anything it touches, so the most effective solution is to cease accelerating so it can't/won't rest against any individual surface.

Lots of room to play with there, and if the limpet latches onto a friendly target, the friendly target will either have the necessary codes to instruct the limpet to detach, or they'll be able to radio traffic control to get that information.

You're looking for gas that increases friction. gas is used all the time to "stop lasers" in most scifi. What people usually don't realize is that increasing friction on a ship will limit its top speed. It's really obvious, but that's what you need to do. My advice? Create your own gas. Don't get too bogged down in the chemicals. Just make it really magnetic. That way you can disperse the gas in space without worrying about it disappointing too quickly while you control much drag it adds. This is more of a concept than a direct answer, but there are a lot of ways you could play this. It depends a lot on how your faster than light travel works too. If it's just your typical fuel shoots out of one end arrangement then you can make the gas really really hot and completely screw over the thermal efficiency of the engine - changing the thermal efficiency changes how much power said engine can make. If it just goes really fast then like I said earlier some dense gas that can increase drag significantly will do the best.

This approach also provides a good explanation as to why your ships aren't slowed, you planned around this. For example you designed your ships to move through this material, or you designed your ships to have the desired thermal efficiency given the unreasonably high temperatures they will experience in your gas cloud - there isn't a ton of heat transferred due to mass in space so any heat transfer would be done by radiation and that's not as efficient as conduction or convection, assuming one isn't moving through a super special part of space.

• +1 for the potential in the story to have several colourful euphemisms the crew use for the ship deploying a large amount of gas. – Simon Fraser Apr 19 '17 at 10:54

You could use a technology similar to the LDSI field in Independence War 2: Edge of Chaos. Basically its a field that can be projected via a generator or a missile payload that creates a region of distorted space time, thereby thwarting the ability of warp drives to function by manipulating space time in front and behind them. In the game this merely causes the FTL drive to not function, however realistically, attempting to use the FTL drive may result in its destruction of the drive, or random ship components to be teleported around the region of distorted space, thereby destroying or heavily maiming the ship.

My assumption is that you're interested in something like a "mud ditch" that will slow down/prevent things moving through the area quickly but not actually stop them. This idea has some potential problems depending on what kind of propulsion is being used and would be most effective when wrapped around a planet to make it difficult to escape quickly compared to deployed in an 3 dimensional area to "catch" passing ships like a net.

Increased Inertia

Based on the idea of "inertialess drive" from the E.E. Doc Smith books, where "going inert" allows for almost infinite acceleration with little energy expenditure. Depending on the intended deployment, having some method that increases the inertia of an object such that the normally fixed amount of acceleration available by the ship's drive is rendered borderline useless.

Localized Energy Drain

Another idea would be some sort of localized energy drain which would then limit the amount of energy available to the propulsion systems. Something like a ray/field that binds electrons more tightly to limit their mobility and ability to transfer energy.

Find a hydrogen cloud. Seed it with oxygen with your missiles. Some how detect when a ship approaches, one spark and an impassible blob of water. They will have to slow way down to pass through it. It will also absorb the heat from there engines to further slow them down

You will have to gradually increase the density if you don't want the impact to destroy the target ship.

If you really want to muck up relativistic maneuvering in a region, why not think BIG? Engineer a Coronal Mass Ejection to flood the area with stellar gas. And/or use a nuclear shaped charge to create a massive plasma spike, and use the associated current pulse to disrupt the coronasphere. Maybe you can divert a bunch of interstellar hydrogen, or disrupt it in a useful way. If a ship is designed to fly through homogeneous interstellar medium (diffuse hydrogen plasma) and you find a way to shock it into ribbons and clumps, then you can metaphorically carve a bunch of potholes in their spatial highway and subject their ship and drive to peak loads and vibrational harmonics for which it was not optimized.

Approximating a mine field is a fair choice. If the pursuer, a third party, or nature, have seeded the area with discrete masses, then triggering them to detonate, or vaporizing them with a directed energy weapon, could create a stationary cloud of gas or particulate debris that imposes a substantial navigational hindrance. Perhaps there is a complex game of cat-and-mouse as the lead ship detects and avoids anything larger than, say, 1mm diameter (as part of normal relativistic navigation), while the pursuing ship tries to scan ahead and find baseball-sized objects to obliterate with directed energy to create unavoidable, dangerous debris clouds.

Other than seeding space, delay tactics would depend heavily on the drives being used. A directed energy weapon that is insufficient to harm a ship directly might still be tuned to match a key harmonic and disrupt a drive. If the target uses an ion drive, would it be possible to hit them with an electron beam and increase their bulk charge enough that the ion drive loses efficiency? If they are using a Bussard ramjet, any disruption in the stellar medium disrupts their drive. In that case, CLEARING THEIR PATH slows them down.

Ships need to radiate waste heat. Disrupt radiation, and you force the drive to operate at a lower level. An energy weapon that doesn't burn a ship can still overheat it, forcing it to reduce drive power. Modify space to make it more opaque, or reflective, to IR wavelengths. Create an artificial, hot nebula nearby.

In general, firing a missile to pass the pursued ship and detonate, creating a cloud of debris, WON'T work; The debris cloud's initial condition is one of matched speed with the pursued ship. Flying through a cloud of gas which matches your speed isn't much of an impediment. That is, unless their drive itself depends on specific properties of the diffuse plasma through which they fly.

What could slow down something traveling at the speed of light? The speed of gravity sounds plausible in relation to black holes and gravitational singularity.

Get yourself a handwavium device which puts two black holes along the ships travel path perfectly equidistant from the left and right side of the ship. Placement and strength of the black holes must be perfect so that the ship is suspended instead of being sucked into oblivion.

Assume a device capable of manipulating wormholes, where the shape of the mouth can be sculpted to a hemisphere.

A black hole located at the far side of wormhole it being positioned almost directly on the event horizon. The output of the other half of the wormhole device would produce a hemisphere effect, the diameter depending on how "open" the wormhole is. The local, weaponized side of the wormhole would have the same properties as the event horizon - localized gravity, time and space distortion. It'd freeze ships in place at the cost of not being able to be interacted with until the device is shut down.

Near-miss nuclear detonations.

A battle begins. The enemy launches missiles at you from far, far away. Fortunately, your anti-missile defences are pretty good at intercepting missiles at close range and none of them get close enough to vaporise your ships. Unfortunately, your enemy knew that was likely to happen, and programmed half their nuclear missiles to explode before reaching you, in a two hundred kilometre wide hemisphere around your carrier group.

Your ships' radiators are now hot from the nuclear glow. You have no way to dump waste heat until they cool down. Every megajoule of energy your crews pull out of their power plants to fight the battle brings them a second closer to boiling alive in their own sweaty pressure suits. You can gently push missiles away from the ship and have them fly away under their own power, but there's no way you can run the ship's engines at anywhere near full power for more than a few seconds.