Can anyone win a "game" of Rocket Tag on an interstellar level against a prepared opponent?

Question

Relativistic Kinetic Kill Vehicles (RKKVs) are all but undetectable until it's far too late to do anything about them; they have a very low radiation profile once at cruising velocity, their exhaust plume is also, by definition, pointed away from the target while accelerating. They're almost impossible to intercept at cruising speed because once you can detect them they're not there any more; that close to c any signal lag kills your ability to track them. And they're, relatively, cheap compared to weapons that do less damage with more precision.

Several answers to this question suggest that warfare in settings where settlements are disparate and thinly connected stand a good chance of turning into an interstellar Rocket Tag scenario in which any time anyone fires a shot it destroys a star system wholesale. When I asked the question I didn't have a clear mental image of what that might look like; then this year I read The Killing Star

which opens with the almost total destruction of humanity over the course of a few hours by an interstellar civilisation using a system wide relativistic kinetic bombardment.

The parallels to another scenario in the universe of the above question made me think about the fact that anyone who knows their enemies have the capability to fire such weapons, and matches it, can still retaliate, possibly even after everyone is dead. They can leave RKKVs cold in space until the incoming munitions have committed to targets, or even until after they've hit, these undetectable arms can then take a bearing on possible source stars for the attack and hit back. Possibly they even simply target all neighbouring star systems in case someone got clever with the vectors.

To me, at first blush, this situation appears to be a clean cut case of MAD, and even a classic case in the political sense as well if everyone knows that everyone is armed. So, apart from an asymmetric case like that in The Killing Star wherein an actor fires on someone who is unable to launch their own relativistic munitions, can one win at interstellar Rocket Tag?

Edit for clarity

Universe specific information; High relativistic speeds (greater than 0.90c) are commonplace, near neighbours stay in sporadic contact trading in IP, read new tech designs and artworks, is common, physical goods are not. Transportation of colonists and labourers outward from overpopulated systems occurs regularly but tourism is virtually nonexistent. Polities encompassing whole solar systems are common and larger, but rather theoretical, leagues do exist kept together by digital diplomatic packets rather than physical embassies. Any ship moving between worlds can and does act as a spy, by deliberately investigating particular issues for a fee and/or just by selling their sensor records at new ports for those who want to catch up on the news from abroad.

Answer 1

Be a Moving Target

Any star system can be targeted so the solution is to not be at any star system.

If you were in artificial world ships travelling through the empty space between stars or even between galaxies, they can't hit you.

Throw in random path wandering and their chances of hitting are virtually zero as space is really really big.

Answer 2

Do not play the game or detect early

There are two ways to win. First is not to play the game. You see that with the nuclear standoff. Any move that entails actually firing a missile leads to an escalation that reduces the warring nations to nothing, and probably much more collateral. And do you want a remaining country like Luxembourg take over the world? I think not.

Detect early

The second way can reduce your enemy to dust, while staying out of harms way. The RKKVs are going 0.9C (maybe faster?), which means you can communicate faster than the RKKVs. That, plus the huge distances, gives you time. Next to the RKKVs you launch, you launch detection satellites. They will position at several distances between you and the target, beaming information back at the speed of light. These have a good chance to detect the enemy RKKVs, as they float in deep space with little distorting sources. Even if they don't detect the RKKVs before they pass, they certainly do after from the plume or sheer proximity and/or active detection mechanisms.

That means you can beam information about where they are back to your defences. If you know when and how they are coming, they can be nudged out of position or destroyed. With the galactic distances what they are, you can have a good time to react. There's probably good ways when and how to launch with certain expected speeds and when positions of the RKKVs are still reliable from detection. A way to detect them at A, then when they are detected again at B for their exact positions your anti-RKKV measures should be right there to take care of it.

That being said, having communication reach you and you only have 10% of the time left to react can make anyone nervous. If you can truly nudge them out of position or destroy them on time depends a lot on how far the systems are apart. To truly nip this in the bud, you want to destroy them when the enemies RKKVs start accelerating. When your RKKVs arrive, you should already have secondary small RKKVs that arrive later, that are able to detect and adjust their trajectory to impact enemy RKKVs before they pose any danger.

To do that correctly, probably you want a long line of detection satellites that pass through the enemy star system at intervals from the moment your RKKVs hit until your counter wave arrives, each communicating any possible RKKVs.

Information war

The question then becomes why this isn't done in the first place. Placing any detectors between you and the enemy can assist you with detection and possible evasion of annihilation. The same is true for moving your population with huge star ships. Likely both sides will try to monitor the situation, detecting any movement and adjusting the RKKVs accordingly. Eventually this can be resolved in only two ways. One is to not play the game, the other is to defeat the detection in any way possible. Destruction, obfuscation, confusion, hacking, overwhelming by sheer number if RKKVs or whatever.

My bet would be not to play. The advantages of using so much energy to destroy a potential opponent seem minimal compared to using it for expansion of any form. The danger is simply too high to play.

Answer 3

Let's start with a few assumptions:

The belligerents hate each other. The reasons for that are quite unclear because by nature of having no trade relations and no immigration, I don't really see a way for conflict to ever escalate to "we'll glass your homeworld" levels. Let's just say that they do hate each other and would glass each other, were it not for MAD doctrine.

Almost everyone lives on, or in orbit of, a planet susceptible to be completely destroyed. This is a given because logistics dictate so: you need to get power somehow, and space is full of a whole lot of nothing, so solar needs you to be close to a sun (potential target), nuclear requires you get isotopes from a world, not even thinking about actual supplies.

Under these principles, you're right that this is a classic example of MAD. Unless you can find a way to stop these RKKVs in-flight, which is impossible, as a potential target, you need to set up a counter-strike force in deep interstellar space, and either commit mass genocide as collateral damage or have it accurately target whoever killed you (not that it really matters. If you're hit you're dead anyway, nobody is going to prosecute you for war crimes).

As I see it, the only way to change this dynamic is by changing the assumptions. Either you manage to negotiate peace under MAD (just like on current-day Earth), and your problem isn't really resolved, or:

You move everyone away from targets. The system-wide government enacts a plan where they launch the RKKVs, then after that (so that it is impossible to see happen remotely until the weapons have already hit), you have all the travel time of the weapons to put everyone on ships, and send them into deep space to live lives as voidborns, where they're untargetable because your enemies can't learn where they're going until after the weapons hit.

The problem essentially boils down to "what can we do to make the enemy unable to target us until after the first strike?" and one answer is arcologies. Another answer, depending on your technology level, is to alter the orbit of targets, but at that technology level, the weapons could realistically make the local sun go nova and you're going to have trouble moving a sun.

Answer 4

Place yourself on a relativistic vessel, that goes as fast as the RKKVs to always outrun or outmanouver them. A society of "spacers" who fly about and rarely stop except for refueling is impossible to target.

That, and make sure the Spacers use a form of Von Neumann-style self-replicating ships, and CLONE THEMSELVES along with their ships, so they become like an exponentially growing infection of the universe, impossible to eradicate with RKKVs, or any other realistic weapon for that matter.

Answer 5

Frame Challenge: You are grossly overestimating the effectiveness of RKKVs

First of all, an RKKV is going to be less powerful than the warheads that a civilization at a given tech level could conceivably design. The only science-based way to get an RKKV up to 0.9c is through the expenditure of mass into energy which means you need to have a nuclear power source, account for all of its inefficiency, and then compound it by the inefficiency of your propulsion system. So, if you assume your propulsion system is 70% efficient, then making a RKKV that can hit with 35 megatons of force will consume the same amount of fuel as a 50 megaton warhead made using the same tech level. So, even if your setting has the high efficiency anti-matter containment that would be needed for such high speeds, you should expect to need litteral tons of fuel and infrastructure for every kg to mass you want to get up to those speeds.

Furthermore, you can not make a RKKV into an accurate weapon for the same reasons hypersonic missile struggle so much with accuracy. At those speeds, even against the relative vacuum of space, your RKKVs will run into enough matter to develop a plasma envelope that will blind the RKKV's sensors and communication systems meaning that once it is up to speed, its flying blind. These missiles can't see thier environment to know how to make course corrections, and they can't possibly predict the exact "atmospheric conditions" of all of the space between two points to be able to precalculate an accurate trajectory. So, if you were to try to launch one from one star system to another, you'd be lucky to even hit the goldilocks zone, much less an actual planet, much less an actual target on the planet.

This means that the only way to hit something as small as a planet is to fly into the solar system and slow down enough to lose you plasma envelope so you can see and make course corrections, then get close enough to the planet to be able to launch a much smaller secondary RKKV so that your can hit the planet... but unless your RKKVs can go from zero to 0.9c almost instantly, there may not be an actual distance where you have enough room to accelerate your weapon while still being target accurate... and target accuracy is important. It would take 10,000s of nukes (or similar sized RKKVs) to actually depopulate an Earth sized world through random bombardment, but 100 or so well placed guided nuclear weapons could wipe out all of a planet's major city's sending the whole planet's economy into ruin neutralizing the planet's threat to you without having to fully wipe out its inhabitants. So... all of this is to say that weather you want to use slow nukes or RKKVs, you need to get really close to a planet while moving at relatively low speeds to be able to attack it.

This gives the plant plenty of time to deploy a fleet to intercept you while you are trying to "slow boat" yourself into a good bombardment position. Also, assuming the RKKVs need time to speed up, there will be a window of time where they are moving way less than 0.9c where you will have time to respond by shooting it down with long range lasers or launching interceptors to take them down before they can reach your world. This also takes away all of your presumptions that an RKKV might be a stealthy weapon because you have to wait until you are close to accelerate it.

Answer 6

MAD relied on the fact that both parties could survive in some form long enough to retaliate. It also relied on the fact that both parties could detect a nuclear strike ahead of time.

Point being, for MAD to work you need to be able to survive long enough to strike back.

A properly coordinated RKKV strike could kill every inkling of life in a solar system and every surrounding solar system simultaneously. Once you've fired, you can safely assume nobody is firing back.

Even if they have "cold" RKKVs waiting to fire off, as the name suggests, they're cold and therefore venerable, so just make some of your RKKVs into relativistic canister shot. Shower the entire solar system with relativistic shrapnel before the main show to eliminate any nasty surprises.

Also I highly doubt they would be undetectable if they're stationary, to get an object up to relativistic speeds it needs ALOT of fuel and therefore a very large rocket. Even if your using antimatter, your still looking at a very large object presumably orbiting a star. Which then of course needs to start accelerating which takes time, even with the best fuels and optimal conditions there's still a fairly wide window where its vulnerable.

Also RKKVs aren't undetectable, in their dormant state they would likely be orbiting something, they would first have to escape that bodies gravity. That initial launch could be detected if you had the right equipment. For example if you were monitoring a solar system you've fired at.

RKKVs are extremely overpowered, the second we discover another intelligent civilization, its a race to see who can build an RKKV first.