Sci-Fi Spergin: Space SLAM

[LostCosmonaut]

A ringworld is a world in the shape of a ring (shocking!). The most well known ringworld is the one from the Larry Niven novel;

 

 

Which encircles a star similar to the sun.

 

(Things like Installation 04 from the Halo series aren't usually considered to be ringworlds, since they're just circular things floating in space not encircling a central body.)

 

Among the many issues with the eponymous ringworld (aside from its graviational instability) was exactly what it was made out of. At a radius of about 150 million kilometers (1.5*10¹¹ meters) and producing about 1g of gravity on the inner surface of the ring, it would have to be made of an absurdly strong material (wiki says it would have to be about as strong as the strong nuclear force). This is unlikely to be possible with any current or near-future technology.

 

Stress in a rotating ring is given by the following equation;

 

σ_z = ω² ρ ( r₁²+ r₁r₂ + r₂²) / 3   (2)

where

r₁ = outer radius of ring (m)

r₂ = inner radius of ring (m)

 

(via http://www.engineeringtoolbox.com/stress-rotation-disc-ring-body-d_1752.html)

 

ω is the angular velocity in radians/second, it can also be written as v/r

Also, as is well know, a = v²/r, or v = (ar)^1/2 

In other words σ_z  = a*r/r²*ρ *( r₁²+ r₁r₂ + r₂²) / 3

As stress is proportional to the acceleration and radius, reducing both means that the ringworld material will have to be less strong.

 

According to wikiped, white dwarfs could potentially have a habitable zone around .005-.02 AU. .005 AU is about 7.5*10⁸ meters (we're using the smaller value because anyone building a ringworld has probably invented air conditioning). We'll use a density of 5500 kg/m³ for the ringworld material, about the same as Earth's total density. Additionally, to simplify our analysis, we'll assume that the inner and outer radius are equal (with a thickness of about 10 km, the difference between r₁ and r₂ gets lost in sig figs.)

 

Plugging our values into the above equation, we get σ_z  = 4.4*10¹³ N/m², or 4.4 TPa. This is dozens of times stronger than steel, or even absurd tungsten alloys. But wait!

 

According to wikipedia and various  other sources, carbyne has a Young's modulus of roughly 32 TPa, well above what we need. True, carbyne (basically polymerized acetylene) has never been made in quantity and would probably react exothermically if it depolymerized, but still, it can be done!

 

tl;dr If you want to make a ringworld, put it around a white dwarf and make it out of acetylene.

 

 

 

 

[LostCosmonaut]

Everyone here is probably familiar with Pluto/SLAM, one of the most nightmarish hilarious weapons proposals from the Cold War.

 

link for plebs

 

Some people here are probably familiar with Relativistic Kill Vehicles, a frighteningly devastating weapon that uses the power of physics to utterly ruin things.

 

SCHV IN SPACE

 

At velocities near the speed of light, the normal KE = 1/2mv² equation for kinetic energy becomes a bit inaccurate. Instead, you use this equation;

 

If v is low, that term on the right comes out to just about zero. However, if v is .9c, then it comes out to about 1.29. v = .99c takes it up to 6.08. This lets you get ridiculous amount of energy out of very small masses. As in, megaton yields out of something no bigger than a baseball. 

 

This massive amount of destructive power makes RKVs incredible attractive as a weapon, especially in a world where faster than light travel does not exist. Their high speed gives them an additional advantage; the target will have very little time to react before the weapon's impact. Suppose an RKV travelling at 99.9% of the speed of light and targeted at Earth was detected as it passed by Jupiter. By the time the light from the RKV (at Jupiter) reached Earth, the weapon itself would be a bit outside the moon's orbit and only seconds from impact. (As a bonus, any incoming light from an RKV is going to be incredibly blueshifted, so you probably won't see it in visible, but as a burst of X-rays or gammas).

 

Their high velocity also makes them incredibly difficult to intercept. Blowing apart an RKV just before impact means that you're just getting hit by a shower of extreme velocity particles instead of a solid slog. All of that ridiculous amount of kinetic energy is still getting dumped into your planet/moon/space station.

 

However, they do have a couple drawbacks. First, it takes a ridiculous amount of energy to accelerate a projectile up to 99% of the speed of light. That means you either need a ridiculously powerful planet-based energy source, or gargantuan amounts of fuel. The second is that if you're just using a slug of metal as your projectile, it is unguided after launch. That means you better know exactly where your target is going to be.

 

In the far future, it might be possible to solve this problem using a quite ingenious invention, the fusion ramjet; https://en.wikipedia.org/wiki/Bussard_ramjet

 

Fusion ramjets harvest interstellar gas (mostly hydrogen) and fuse it to create thrust without the need for onboard fuel. Their feasibility is uncertain, and most things I've seen has their speed limited to about 50-75% of the speed of light. Let's suppose it's possible to make a better version, capable of 99.99% of c (we'll call it a fusion scramjet, because scramjets are cool).

 

Build your fusion scramjet, and load onto it up with 10,000 ten kilogram slugs of metal. Your scramjet's probably about the size of Saturn V at this point, but if you're advanced enough to build a fusion scramjet you don't give a shit. Point the scramjet at whatever star the hated alien species' home planet orbits around, and let it rip. On its way there, the fusion scramjet accelerates to 99.99% of the speed of light, gaining ridiculous amounts of kinetic energy. On final approach to the target, lock on to the enemy planet, make final course corrections, and dump the slugs. Each one will hit with more energy than the 1960 Chile Earthquake, and there's 10,000 of them. Your enemy's home planet will cease to exist. The scramjet can fly off happily into the void, of if you're feeling vengeful, you can crash it into the planet as well.

 

Actually, let's revisit this setup. You don't need to completely erase the planet, just render it uninhabitable. Ten slugs should be enough to do it. Also, let's go a step further an suppose that you and your species are genocidal dicks who don't care who you kill. (The inhabitants of the planet Krikkit approve.)

 

Build several dozen fusion scramjets, each loaded with 10,000 ten kilo slugs as before. This will be a significant expenditure, but not insurmountable for an advanced enough society. Dump them into distant orbits, out in the Oort Cloud or Kuiper Belt where they can be virtually undetectable. Program them to listen for a certain signal. If that signal stops, the fail-"safe" triggers.

 

Each scramjet points in a different direction and activates a primitive guidance system. It picks a suitable star (K, G, or F class) within a couple degrees of its nose and accelerates toward it. When it gets near the star, it listens for planets emitting electromagnetic radiation characteristic of an industrial civilization. If it finds none, it picks another star along its general direction of flight. If it does detect a civilization, the scramjet alters course to do a close flyby of the target. As it does, it ejects 100 slugs on an impact trajectory. The total energy of the impacting slugs will be near what Shoemaker-Levy 9 hit Jupiter with, but spread more evenly across the surface. Massive ecological damage and extinctions will result. The best part is, your scramjet has enough payload to do it 99 more times!

 

Using a number that is definitely not pulled out my butt, we'll assume that we encounter a suitable target every 50 light years. With a decently sized (but not excessively large) fleet of automated fusion scramjets, you could wipe out industrial civilizations within a 5,000 light year radius of yourself. Great for civilizations that value privacy!

[Meplat]

Long ago, I dealt with some less than sharp folks in a quasi RPG, wher at best I offered bits of amusing trivia or snark...

The one that basically ended things was "Tachyon clad neutronium shot" ..

 

As in "Uber baddie (trek, star wars, or other) encounters a fairly large ship with zero "energy" weapons but massive "mass" armor. "

After some (obviously) failed negotiation, fire is exchanged. Hmm, armor made of compressed neutrons is fantastically tough shit it seems.  (No really. it took me a LONG time and a few cases of beer to figure this out)

 

And wow, 37mm Neutronic shot fired at trans relavatistitic velocities at massive volumes tends to do nasty things to near any sci-fi ships. 

We'll not go into fourth dimension singularity mines, nor point-location fold charges.

 

Seems having a friend who is both a hard core sci fi freak and possessing more than a few doctorates in subatomic physics, plus my "keep it simple" vibe runs some wrong.

 

I won't go into " ships massing  in the same range of large solar systems" or similar. People with multiple doctorates who like sci fi are scary,,

[Sturgeon]

Build several dozen fusion scramjets, each loaded with 10,000 ten kilo slugs as before. This will be a significant expenditure, but not insurmountable for an advanced enough society. Dump them into distant orbits, out in the Oort Cloud or Kuiper Belt where they can be virtually undetectable. Program them to listen for a certain signal. If that signal stops, the fail-"safe" triggers.

 

Each scramjet points in a different direction and activates a primitive guidance system. It picks a suitable star (K, G, or F class) within a couple degrees of its nose and accelerates toward it. When it gets near the star, it listens for planets emitting electromagnetic radiation characteristic of an industrial civilization. If it finds none, it picks another star along its general direction of flight. If it does detect a civilization, the scramjet alters course to do a close flyby of the target. As it does, it ejects 1,000 slugs on an impact trajectory. The total energy of the impacting slugs will be near what Shoemaker-Levy 9 hit Jupiter with, but spread more evenly across the surface. Massive ecological damage and extinctions will result. The best part is, your scramjet has enough payload to do it 99 more times!

 

 

Today I learned that 10,000/1,000 = 100.

[Vanagandr]

I think this is called a 'chaos dunk'

[LostCosmonaut]

Today I learned that 10,000/1,000 = 100.

My bad, I converted from imperial to metric numerals incorrectly.

[Donward]

My bad, I converted from imperial to metric numerals incorrectly.

APOSTATE!

[LostCosmonaut]

APOSTATE!

hail mks

[LostCosmonaut]

MIT examines the potential of ravioli as a weapon in space; http://web.mit.edu/starflt/Temp/ravioli