What future space combat would really look like • Hacker News Board

Re: What future space combat would really look like

#141

Post by bayleo » Wed, Dec 28, 2011, 1:05 AM UTC

yock wrote: post #19

rw wrote: post #14

Earlier quoted context omitted.

An example: Project Thor / "Rods from God": http://en.wikipedia.org/wiki/Kinetic_bombardment

The linked article seems to mention re-entry friction as a problem yet-to-be-solved: The system would also have to cope with atmospheric heating from re-entry, which could melt the weapon. Then there's the question of whether or not heat is truly the most immediate issue. NASA and USAF had to actually fly an airplace near and past the speed of sound to see how the properties of the atmosphere changed when compressed.…

The article mentioned tungsten, which has an absolutely preposterous melting point. I doubt it would melt moving at typical orbital velocities, but even if it were to be moving faster you could easily make the front of the projectile ablative.

Re: What future space combat would really look like

#142

Post by jrockway » Wed, Dec 28, 2011, 1:08 AM UTC

troels wrote: post #115

talmand wrote: post #95

Earlier quoted context omitted.

What if the goal is to eliminate the planet-side species? Plus I'm willing to bet you could obliterate the surface of the planet using kinetic weapons and still have plenty of resources left over.

Why would that ever be a goal?

Because people are irrational. Why did Hitler try to kill all the Jews? Because he felt like it and had the means to do something about it.

Re: What future space combat would really look like

#143

Post by cpeterso » Wed, Dec 28, 2011, 1:11 AM UTC

quanticle wrote: post #7

This essay isn't all that realistic. I found this one [1] to have a far more realistic view of what space war would look like. Tl;dr: it's much cheaper and much more effective to lob comets at your enemy's homeworld than it is to fight with ships. [1] http://www.gwern.net/Colder%20Wars

This is why Carl Sagan argued against projects like Spaceguard that purported to defend against rogue comets or asteroids. He felt that the risk of a space collision was much smaller than the threat of humans turning the technology around to hurl asteroids at our enemies.

Re: What future space combat would really look like

#144

Post by rbanffy » Wed, Dec 28, 2011, 1:15 AM UTC

philwelch wrote: post #81

rbanffy wrote: post #64

Earlier quoted context omitted.

If the outer solar system dwellers become self-sufficient, they would have no need to go down the gravity well of the Sun to have commerce with earthlings. The further out those colonies are, the lesser their contact with Earth will be. If they live off the Oort cloud, the would be about one light year away from Earth and it's very hard to imagine a shared culture with such a communication lag.

Why, exactly, would people dwell in the Oort cloud? The idea of having an isolated, self-sufficient colony in the Oort cloud seems like an even poorer version of North Korea, except you'd have to ship all the people out there. There's no good analogy with colonialism on Earth, because most of that involved getting very very rich by trading with the mother country, and if there's anything to be won, economically, from…

What if the people want the exile? Provided fabrication technology is advanced enough to provide for material comfort, what is the difference between living on a planetary surface or living on a very comfortable habitat? What if you don't like Earth laws?

That same fabrication technology would negate the traditional colonial model. There would be very little need to move physical goods between worlds.

Imagine having a million times more space and material resources than you currently have on Earth now. While the mass on the Oort cloud is a fraction of the mass of the Earth, it's still a lot of stuff.

Re: What future space combat would really look like

#145

Post by brazzy » Wed, Dec 28, 2011, 1:29 AM UTC

sliverstorm wrote: post #129

ohyes wrote: post #88

Space combat seems pointless to me. What exactly would they be fighting over? Presumably you want to reach space for resources, so asteroids, planets and moons with minerals, stuff like that. You might also want planets/asteroids/moons that are 'good' for colonization (easily terra formed or already life sustaining). You probably wouldn't see many fights where you are firing at the resource itself. No one with the mo…

You can argue this over in your head a lot, but it's really quite simple in my mind. If we assume space travel becomes relatively easy (that is to say it is used for more than initial colonization) there will be interstellar commerce. If there is unprotected commerce, there will be pirates. Any time there are pirates, protection will develop. Let us call these peace-keepers the Navy. If you engage in commerce and you…

Read TFA, it argues pretty convincingly that there will not be pirates because A) you can't hide in space and B) Any ship is a WMD, so governments will do anything to keep them out of the hands of criminals, and protection rackets would be a far more profitable use for them than raiding commerce.

Re: What future space combat would really look like

#146

Post by nextparadigms » Wed, Dec 28, 2011, 1:30 AM UTC

troels wrote: post #115

talmand wrote: post #95

Earlier quoted context omitted.

What if the goal is to eliminate the planet-side species? Plus I'm willing to bet you could obliterate the surface of the planet using kinetic weapons and still have plenty of resources left over.

Why would that ever be a goal?

Maybe they are spreading "propaganda" or have "weapons of planet destruction" and we can't let that unpredictable species have them!

Re: What future space combat would really look like

#147

Post by dalke » Wed, Dec 28, 2011, 1:48 AM UTC

cschneid wrote: post #69

dalke wrote: post #56

Earlier quoted context omitted.

I've been trying to get a sense of how effective these scans are. Asteroid 2005 YU55 was discovered 28 December 2005. It's about 400m in width, which is the length of the biggest vessel we have. When it was discovered, it was 0.8AU from the Earth, and its orbit is inside that of Mars. This tells me that 6 years ago we did not know all of the +300m asteroids within the orbit of Mars. How much better are we now? I read…

Asteroids don't pump out waste heat. Things get a lot more obvious when heat differentials are big.

I was commenting on Talmand's scenario; take "three of the world's largest ships, put them together to form one ship and then placed it in a random spot somewhere within the orbit of Pluto; how long would it take you to find it?"

Using the formula in the "Refrigeration" section of the page linked to by Avshalom, the "maximum range a ship running silent with engines shut down" (assuming diameter = 500 m and temperature = 290K is about 500 million km, or about 3.3 AU. That's well within the orbital radius of Jupiter.

That's assuming the entire asteroid is at 290K. Pluto averages about 40 AU out, given a 0.056% chance that a room-temperature asteroid would be detectable.

I'm also uncertain about the reasoning in the page linked to by Avshalom. I think that assumes a 3K background, and I think you also think there's a big heat differential. However, the average temperature of the moon is something like -25C, and if an asteroid were closer to the sun, then the difference in surface temperature between an internally heated vs. sun heated asteroid is well within the errors in measuring the physical properties of the asteroid.

You can even work it out for yourself, using the equation at http://en.wikipedia.org/wiki/Standard_asteroid_physical_char... . I worked it out to:

  166C at Mercury orbit: http://www.google.com/search?&q=(((1-0.1)+*+(3.827E26+watts)+%2F+(0.9+*+Stefan-Boltzmann+constant+*+16+*+pi+*+(0.3+*+150000000+km)**2)))+**+(1%2F4)

  90C at Venus orbit: http://www.google.com/search?q=(((1-0.1)+*+(3.827E26+watts)+%2F+(0.9+*+Stefan-Boltzmann+constant+*+16+*+pi+*+(0.6+*+150000000+km)**2)))+**+(1%2F4)

  5C at Earth orbit: http://www.google.com/search?q=(((1-0.1)+*+(3.827E26+watts)+%2F+(0.9+*+Stefan-Boltzmann+constant+*+16+*+pi+*+(1.0+*+150000000+km)**2)))+**+(1%2F4)

(The values for albedo and emissivity are not well known, so there is a wide error range in this calculation.)

Still, that's enough to show that the heat differentials inside of the Earth's orbit are not that big.

Re: What future space combat would really look like

#148

Post by philwelch » Wed, Dec 28, 2011, 1:57 AM UTC

rbanffy wrote: post #144

philwelch wrote: post #81

Earlier quoted context omitted.

Why, exactly, would people dwell in the Oort cloud? The idea of having an isolated, self-sufficient colony in the Oort cloud seems like an even poorer version of North Korea, except you'd have to ship all the people out there. There's no good analogy with colonialism on Earth, because most of that involved getting very very rich by trading with the mother country, and if there's anything to be won, economically, from…

What if the people want the exile? Provided fabrication technology is advanced enough to provide for material comfort, what is the difference between living on a planetary surface or living on a very comfortable habitat? What if you don't like Earth laws? That same fabrication technology would negate the traditional colonial model. There would be very little need to move physical goods between worlds. Imagine having…

Alright, let's go with that scenario for the sake of argument. What would be the casus belli?

If it's something like rare elements available only in the Oort cloud, the traditional colonial model would apply and the overwhelming interest in the Oort cloud would be in those very rare elements and not as some sort of refuge. Your Oort cloud pilgrims would have to be fiercely protective of their rare elements and to have gotten there first before the rare-element prospectors. The Oort cloud would have to be not big enough to satisfy both groups of people, and the Oort pilgrims would have to be stubborn enough not to move their replicator-colony to the Kuiper belt or elsewhere.

At that point, you can start to reasonably speculate: you have clear objectives on both sides at the very least. It becomes very hard to predict what would happen because we've stipulated so many counterfactuals that everything we know would be obsolete. Logistics, which has dictated almost every war in human history, would look totally different due to the fabrication technology, though limits to propulsion technology and the vast distances involved would cause other issues. The Oort pilgrims would have the advantage of locality--they could see and respond to any movements from the inner solar system within months while delaying or hiding their defensive actions until the last minute. But the fabrication technology would render pretty much anything expendable, and it might be feasible to turn maybe a few hundred Kuiper belt objects into a swarm of self-guiding missiles or something while the Oort pilgrims wouldn't have enough raw materials to really hurt, say, Earth.

Re: What future space combat would really look like

#149

Post by philwelch » Wed, Dec 28, 2011, 2:07 AM UTC

ew wrote: post #58

It was definitely an interesting read, however, I feel that fundamentally, for humans to reach the point where space combat is even feasible we will have solved so many more important problems that there won't be a need for fighting in the cosmos. Earth, in general, is at peace. We are largely struggling against terrorism, radical groups, and internal genocide rather than full scale, nation-on-nation wars. No two dem…

> No two democracies have gone to war, ever

That stirs up a whole new thing, detailed here: http://users.rcn.com/mwhite28/demowar.htm

Re: What future space combat would really look like

#150

Post by dalke » Wed, Dec 28, 2011, 2:08 AM UTC

PotatoEngineer wrote: post #135

sp332 wrote: post #84

Earlier quoted context omitted.

It doesn't matter. As long as each "blob" is heavy enough to resist deflection by the wind, the same total mass will impact at about the same speed. The only downside I can see is that the blobs might hit at slightly different times, which would reduce the instantaneous force on the target. But I think it would transfer the same total energy.

The same total energy would be transferred, but it would be spread out over a larger area. If the area is sufficiently large, then all you've done is raise the temperature of Germany by one degree for a while. (Still, there are plenty of configurations that make good kinetic-kill weapons with a manageable amount of re-entry heat. Think large rods with good amounts of mass and small cross-sections. This is an engineer…

Figuring Germany at 357021 sq. km, and "1 degree" to raise the equivalent of a meter of water by 1 Kelvin, gives 1.5E18 J.

If I did my math right, that's the energy in a 400 megaton bomb, or 17 kg of antimatter. The US nuclear arsenal is about 2500 Mt.

I don't think you'll be able to distribute that much energy so uniformly. Almost certainly you'll end up with all of it dumped into the surface, with people, land, and cities burned to a crisp. Only a few people in mines or deep valleys might survive.