Brainstorming a “Kitchen Sink“ Sci-Fi campaign

[Zardnaar]

That was my point earlier. An actual dinosaur killer size asteroid needs a lot of energy to get enough delta-V to accelerate it out of the Asteroid belt or trojan orbits. Lugging something big enough to do that insystem, and then doing the burn isn't going to be subtle. Even a burn to get it into a minimal energy orbit to intersect with your target planet is going to be pretty hard to overlook.

The minimal estimated size for the Chixulub impactor is about 2x10**12 tons. A minimal Jupiter-Earth transfer is about 3.1km/sec worth of delta-V, and that's an orbit that would take years to make the rendezvous with Earth. Even with a 100% efficient reaction drive, that's about 1.5x10**22J of energy, or equivalent to the explosive yield of 3.5x10**6 megatons that you have to somehow conceal while you accelerate the asteroid. Bearing in mind that at a relative velocity of 3km/sec the kinetic energy of an object is roughly equivalent to the explosive yield of its weight in TNT; attempting to sink even 1% waste energy into the object itself is going to make it quite warm.

A city killer could be a lot smaller, but that's some real precision sharpshooting to hit a city-sized target from Jupiter.

Having said this, although I think we now have a sense of the scale of the effort involved in humping dinosaur killers around a star system, we are also in the business of trying to apply real-world physics to a fantastic setting ...

I wouldn't worry about physics touch but would put that up there in terms of sci fi power. Not ringworlds or dyson level power but probably beyond Star Wars and Trek.

Using small asteroids accelerated a'la Mass Effect better idea.

 

[Eyes of Nine]

Randomly, it would be interesting to have the gates at 90 degrees to the plane of the elliptic

 

[Umbran]

I know this - reaction drives and guidance. It's pretty obvious when you're doing this, as an asteroid big enough to be a dinosaur killer needs a large drive and a naughty word-load of reaction mass to move it in any reasonable length of time.

Dude, we are talking about a culture that can to FTL jumps. They are NOT using chemical reactions to power ships of any sort. So, no huge plume of brightly burning gas to be seen by a telescope. There's probably a nice quiet ion drive back there - little reaction mass used. Cheap. Low thrust, low emissions. Gravity does most of the work for you.

Unless you can accelerate it to velocities in the 1,000's of km/sec it will still take months or years to get to an inner planet from the outer system.

Um, dude. The thing that actually killed the dinosaurs had no reaction mass at all. It just fell from the outer solar system to the inner system. Yes, it takes time. You lack patience, grasshopper?

Okay, so the Earth itself is moving at about 30 km/sec. You can pop a rock out of hyperspace dead still right in its path, and have that much relative velocity. WHAMMO!

If you've ever done an orbital rendezvous in Kerbal Space Program, hitting the sphere of influence of a planet, let alone the planet itself is not a trivial undertaking from (say) Jool to Kerbin. The asteroid will still need terminal guidance or a very precise initial shove indeed to hit the target.

So, what you are saying is... you, here and now in 2020, have the computer power on your own laptop sufficient enough to do that job. So, thank you for proving that the computing power for guidance isn't a barrier....

This will not be prevented by anything as simple as "where do you get the velocity" or "math is hard!" as if our aggressors are frelling Barbie. Which is why I ask why it doesn't happen.

 

[aramis erak]

Here's the secret - when you are dealing with space opera RPGs... the distances are arbitrary. Because you aren't going to have them hex-crawl through the galaxy. For one thing, it is a 3d volume, not a flat map. For another, the number of sites they can reach goes up too fast.

Many RPGs ignore the 3D. Probably the best known of these is Traveller.

For combat, many more ignore local 3D, even while doing 3D for interstellar.

If you go with big enough hexes, you can treat it as a single hex thick. The thickness is about 1 kPc; the Shapley center is 2 kPc across (and tall). It's 120 kPc across the disk.
the LMC is ~50 kpc away, 14 kPc diameter across the disk, probably under half a kpc thick, distorted barred spiral
the SMC is ~ 62 kpc away, between 7 and 12 kpc across, barred spiral
Sag dSph is roughly 50 kpc away from the galactic center, in a polar orbit... and what little I can glean, is a 7x14 stretched sphere.

Note at a scale of 1 kpc per hex, only the center hex of the Milky Way is 2 hexes thick.
The LMC is a 14 hex disk only 50 kpc from earth...
The SMC is a 7x14 oval.

All very mappable.

But at that scale, 1 week per hex means hitting the LMC in under a year, and crossing the MW is 2 years and 2 months, plus another two weeks to avoid the Shapley Center and the Sag A* within.

 

[Nobby-W]

Dude, we are talking about a culture that can to FTL jumps. They are NOT using chemical reactions to power ships of any sort. So, no huge plume of brightly burning gas to be seen by a telescope. There's probably a nice quiet ion drive back there - little reaction mass used. Cheap. Low thrust, low emissions. Gravity does most of the work for you.

This is a straw man argument. At no point did I state the use of chemical rockets. It doesn't matter how you generate the thrust, the energy used is still the same (give or take any waste energy coming off as heat) and the delta-V is still the same.

You're changing goalposts and assumptions. You're making an implict assumption that your technology of choice is stealthy on a scale of shifting a multi-billion ton asteroid. At no point have you stated this assumption or said anything to back up this argument.

Um, dude. The thing that actually killed the dinosaurs had no reaction mass at all. It just fell from the outer solar system to the inner system. Yes, it takes time. You lack patience, grasshopper?

This is a red herring fallacy - introducing irrelevancies. Of course the actual Chixulub impactor had no reaction mass - it wasn't being aimed artifically, but just happened to be on the right orbit to hit earth, so it didn't need it. The discussion is specifically about somebody artifically shifting the orbit of a dinosaur killer.

Okay, so the Earth itself is moving at about 30 km/sec. You can pop a rock out of hyperspace dead still right in its path, and have that much relative velocity. WHAMMO!

You're shifting goalposts again. Now implying that it's trivial to move a dinosaur-killer through hyperspace, a new set of arguments that wasn't brought up before. Nothing offered to substantiate it.

So, what you are saying is... you, here and now in 2020, have the computer power on your own laptop sufficient enough to do that job. So, thank you for proving that the computing power for guidance isn't a barrier....

This is another straw man argument. I never stated that computer power was an issue.

This will not be prevented by anything as simple as "where do you get the velocity" or "math is hard!" as if our aggressors are frelling Barbie. Which is why I ask why it doesn't happen.

This is a hasty generalisation, Just saying it's possible in principle and that some trivial things don't say it can't, therefore it will happen. You haven't engaged further to explain your arguement.

This is also a straw man argument. I never said it was impossible, just hard to do without being noticed and much easier to undo than to do in the first place.

I'm calling you out on this. There's almost nothing in your post that wasn't disingenuous in some way. Please don't do this sort of thing. There's no point in engaging stuff like this if you're not going to argue in good faith. You've avoided the original suggestion, which is that the large energy expenditure needed for the delta-V to shift a dinosaur killer makes it difficult to do without being noticed. Instead you've decided to poo-poo a strawman interpretation of the post with a series of rhetorical devices and introduce your own new set of assumptions without bothering to state them. You're clearly not discussing this in good faith but pulling out rhetorical tricks to win an argument. If you don't want to be dismissed as a troll I suggest you don't engage in this behaviour.

You've previously posed a question about why it wasn't going to happen and I stated a scenario, specifically that the very large energy expenditure makes it hard to do without being noticed. I may not have been clear about defence, but I'll clarify it now. If you catch it early enough, you only need a small amount of delta-v (most efficiently applied prograde or retrograde), to deflect its trajectory so it misses. That's orbital mechanics. Ergo, it's much easier to defend against such an attack than to make it, by several orders of magnitude. That's a conceit that you can put into your game without needing handwavium over and above the assumption that such an attack could be made in the first place. The same technology used to make the attack can be used to defend against it, but only needing to be deployed on a much smaller scale.

That's before one asks the question of whether the scale of this endeavour makes it cost effective anyway - given the fantastically large amount of energy involved, is it cheaper to do it some other way - perhaps just rock up with a fleet of warships and attack the planet in person?

 

[Nobby-W]

I wouldn't worry about physics touch but would put that up there in terms of sci fi power. Not ringworlds or dyson level power but probably beyond Star Wars and Trek.

Using small asteroids accelerated a'la Mass Effect better idea.

The other question is whether this is really cost-effective in the first place. Kinetic weapons are great, but do you need to do it on that scale? Even if you've got the resources to accelerate an asteroid to relativistic speeds, would it just be cheaper to turn up with a fleet of warships and attack the planet in person?

 

[Zardnaar]

The other question is whether this is really cost-effective in the first place. Kinetic weapons are great, but do you need to do it on that scale? Even if you've got the resources to accelerate an asteroid to relativistic speeds, would it just be cheaper to turn up with a fleet of warships and attack the planet in person?

Depends on the sci fi universe. Mass Effect you won't need a very large asteroid.

I'm not sure how many universes can do it. Star Wars sorta can in old legends but it's super weapons/precursor type stuff.

Thinking massive asteroids kilometers across, small ones a few universes can pull that off.

It's more if the galactic standard can do it reliably (Federation, Empire, Covenant, Empire of Man, Gou'Ald etc).

 

[Nobby-W]

Depends on the sci fi universe. Mass Effect you won't need a very large asteroid.

I'm not sure how many universes can do it. Star Wars sorta can in old legends but it's super weapons/precursor type stuff.

Thinking massive asteroids kilometers across, small ones a few universes can pull that off.

It's more if the galactic standard can do it reliably (Federation, Empire, Covenant, Empire of Man, Gou'Ald etc).

The question I put was more along the lines of "Is it cheaper to do it some other way?" There's a lot of handwavium involved in the assumption that you can accelerate an asteroid to relativistic speeds in the first place. One could do the maths, but it will come up with a very large number for even a small fraction of c, potentially even bigger than the dinosaur killer scenario. Also, at relativistic speeds, the impactor itself becomes vulnerable. Just getting something to collide with it on the way in could be enough to destroy it or scatter it into pieces harmlessly.

What was asked was "Why can't somebody do this?" The argument against it could be something along the lines of "Yes, you can do it, but it's infeasibly expensive due to the amount of energy involved, and comparatively easy to defend against. It's several orders of magnitude cheaper to warp a battlefleet into the system and attack the planet with that."

This argument turns up in Traveller circles on a semi-regular basis due to some poorly thought out setting conceits. IMO your core setting conceits are broken if you can't think of a reasonable way why folks don't do this. You don't have to look past first-year physics to come up with some impressively large numbers and say "Gosh, that's several major industrialised economies worth of output just to supply the energy to do this. There's got to be a cheaper way."

 

[Zardnaar]

The question I put was more along the lines of "Is it cheaper to do it some other way?" There's a lot of handwavium involved in the assumption that you can accelerate an asteroid to relativistic speeds in the first place. One could do the maths, but it will come up with a very large number for even a small fraction of c, potentially even bigger than the dinosaur killer scenario. Also, at relativistic speeds, the impactor itself becomes vulnerable. Just getting something to collide with it on the way in could be enough to destroy it or scatter it into pieces harmlessly.

What was asked was "Why can't somebody do this?" The argument against it could be something along the lines of "Yes, you can do it, but it's infeasibly expensive due to the amount of energy involved, and comparatively easy to defend against. It's several orders of magnitude cheaper to warp a battlefleet into the system and attack the planet with that."

This argument turns up in Traveller circles on a semi-regular basis due to some poorly thought out setting conceits. IMO your core setting conceits are broken if you can't think of a reasonable way why folks don't do this. You don't have to look past first-year physics to come up with some impressively large numbers and say "Gosh, that's several major industrialised economies worth of manufacturing capacity just to build the hardware to do this. There's got to be a cheaper way."

There's no real answer to that. Depends on the power level of the weapons.

An asteroid bomb requires a lot of nuclear bombs or a sing weapon in Warhammer 40k or Dune. If you just want to wreck or glass a planet.

Star Wars requires a fleet or kamikaze super star destroyer.

 

[Nobby-W]

There's no real answer to that. Depends on the power level of the weapons.

An asteroid bomb requires a lot of nuclear bombs or a sing weapon in Warhammer 40k or Dune. If you just want to wreck or glass a planet.

I think that's the point. You're designing setting conceits. If you want to answer "Why don't folks use dinosaur killers on a regular basis?" then you just tweak the capabilities of the societies so they can't. I just used some basic physics to show a few lines of argument that could be used - 'too big', 'too noisy to hide', 'too easy to defend against', and 'cheaper to do it some other way.'