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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 muc

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 http://www.gwern.net/Colder%20Wars

makmanalp 15y ago
Ender's game spoiler alert! Hope it doesn't ruin it for anyone else... (grumble.) Anyway, how the heck does one lob a comet? If throwing one was so easy, why wouldn't they just throw it right back at you?
- quanticle 15y ago
  Well, both gwern's essay and the essay linked by OP assume that both sides have ships capable of interstellar travel. In gwern's case the idea is to not bother with the ship; just bolt an interstellar drive to a comet and point it at the enemy's homeworld. As for them throwing comets back at you, that is addressed in the essay. In short, there is nothing stopping them from throwing comets back. Space war will resemble the Cold War much more than any active engagement. Mutually assured destruction will be the overriding doctrine.
- aaronblohowiak 15y ago
  Do you really need a spoiler alert on a young-adult novel that has been out for 26 years?
  - blake8086 15y ago
    It's not like they stopped making young adults 26 years ago.
- patio11 15y ago
  Physics. Attacker gets arbitrary mass (reactant, etc) and time to accelerate. Defender needs same mass/time to decelerate... after discovering the attack. Note that you could literally prep an attack for millennia which would be discovered a matter of hours prior to ending a civilization. Physics makes for sucky narratives. Good thing it also makes for a vast, dead, boring universe.
  - Tichy 15y ago
    I don't think you would try to slow down approaching meteorites to zero speed, only deflect them a little so that they miss the planet. The further away you catch it, the less energy it takes (I assume, didn't do the maths).
    - kbolino 15y ago
      Debatable. On the one hand, the farther the projectile is from the planet, the less it needs to be deflected. On the other hand, you have to expend energy to get to the damn thing in the first place. I suppose the survival of your species renders moot most energy concerns though.
    - quanticle 15y ago
      It depends on the momentum of the asteroid. If I've accelerated an asteroid up to .5c, then even if you discover the attack years ahead of time you might still not have the energy to deflect the asteroid by enough to save your planet. You also have to remember that the attacker can launch multiple simultaneous asteroids. You might have enough nukes to deflect one asteroid. Do you have enough to deflect ten? A hundred?
      - russell 15y ago
        If you can accelerate an asteroid up to .5c, you have harnessed energy resources to power the earth for a gazillion years. You would be so rich that you dont need to be a warlord. You could become ... a banker. Actually, at .5c from the Kuiper belt, the warning time is only 30 hours or so and the momentum is such that deflection is impossible. I'm too lazy to do the math but the collision would be spectacular.
      - nialo 15y ago
        Momentum doesn't really work this way. The only things that change the difficulty of deflecting something are it's mass, and the remaining time to impact. Having a lot of momentum doesn't change how much force is required to give something a given acceleration until relativistic effects start to matter. (I guess distance also makes it harder, because you need to travel further to start deflection, but that's not really a momentum thing)
- talmand 15y ago
  Spoils Ender's Game? Bummer. I recommend you read it anyway.
meric 15y ago
I postered a comment on the essay, I'll repost it here: You assume the interstellar species will be living on a planet. What if they hollowed out their planet of resources long ago and now live in a cloud of asteroids instead? Asteroids are hollowed out as giant fortresses in space, and a bio dome sphere thingy built inside. As they are living in an asteroid cloud, to prevent impact they would have to attach thrusters to each asteroid they live on to dodge other asteroids. So the asteroid from kuiper belt attack won't work... but what if the asteroid was launched at close to speed of light? 1. That would take a very big amount of energy. 2. They would've had to carry the energy to the kuiper belt. 3. They would've been noticed and a fleet would've sent in to capture it before the asteroid was launched. What about the nuclear bomb? Well they live deep in the asteroid, it'll protect at least against some nuclear hits. If one asteroid blows up there are still 499 others. Still it would be great to prevent the loss of sentient life... Also what happens if 500 nukes were launched at each asteroid? I've got no answer to that. I do wonder if there could be a device that would force nuclear explosives to be triggered prematurely, lets say, 2km away. That would be sufficient to protect the asteroid.
- quanticle 15y ago
  What about a shotgun approach? Take a comet, accelerate it up to a significant fraction of lightspeed (after all, you you have lightyears in which to do so), and trigger a bomb in the comet to blow it apart into a few smaller pieces, each traveling at a significant fraction of c. Rinse and repeat.
  - 46Bit 15y ago
    That's probably the best suggestion here. Not as easy to deflect something like that.
  - meric 15y ago
    I've made another reply at the site: So the invading force goes into the Oort cloud, picks a chunky rock, attaches a giant thruster to it and begins accelerating it towards c. A day later, the speed of the rock has reached 0.5c. Hours later, a defending fleet arrives, shoots and kills all the invading bds. The rock however, continues at 0.5c even though the thruster and guidance systems were destroyed. It reaches the asteroid cluster, and hits... nothing. It keeps going to the other side of the solar system, and as its speed was so high, exits orbit. Accelerating a giant rock to c takes throwing out alot* of gas. The asteroid based civilisation, to prevent random impacts with random asteroids, would've been tracking every object in the belt. One of the rocks suddenly accelerates, I think it will be picked up. Also, when the asteroid was accelerating, its direction would've been picked up. Once accelerated to c, it will still take hours to arrive at the designated target. The home asteroids simply have to maneuvre away from an intercept course. And no, guidance systems on the accelerated rock won't help. It's travelling at c, and by the time the system finds out the target has moved away, the asteroid would've missed it. Unless the asteroid have 100% maneuverability, and energy to change course whenever, however it likes. But if the asteroid can do that, any asteroid can do that. ;) So your only option is accelerating the rock from the next system onwards. It will now take years for the asteroid to arrive. To reduce the probability of a successful attack, just have a "random thruster day" every 30 days where all the home asteroids just move randomly to different locations. By the time the enemy asteroid arrives the location of all the home asteroids would've been different. The probability of hitting anything worth hitting will be very low. Even if you have 1000 incoming asteroids. Also you're assuming you won't get picked up accelerating an asteroid to c in the next system; Remember, asteroids have no atmosphere and 100% visibility. You might miss 1, but 1000? I'd doubt it. if 1000 asteroids are really incoming then you just make every day random thruster day. ;) They have so much energy, you should too.
zeteo 15y ago
The fighting methods in that essay still require ships (to sneak up into e.g. Kuiper's Belt). In any case, a big, dumb projectile can have its course changed with much less energy than required to fire it. The bigger it is, the earlier it will be detected; and the faster it goes, the smaller the angular deflection needed to miss its target.
- pilom 15y ago
  While it is true that it should be easy to deflect, it is only easy to deflect if you can detect it. The essay assumes that the projectiles would be pushed to a significant fraction of the speed of light. At that speed there is no time to launch any type of deflection.
  - zeteo 15y ago
    The energy required to accelerate a big object to even half the speed of light is prohibitive. Even if the process was feasible, it would be a vast cosmic event bound to emit some radiation, which would still arrive much sooner than the object itself.
    - quanticle 15y ago
      Well you don't have to accelerate it all at once. Remember, this is space war, and we're playing for keeps. Spending a millennium to accelerate a rock up to .5c might be worth the trouble.
      - zeteo 15y ago
        If you take longer to accelerate it, that just increases the probability of detection by other means. It still doesn't change the argument that it should be much cheaper for the defender to detect and deflect your projectile than it was for you to launch it in the first place. Not to mention that an unmapped interstellar gas cloud, or an undetectable asteroid, is all it takes to deflect the projectile a few millionths of an arcsecond and make it miss its target.
- 15y ago
dhs 15y ago
The "bugs" in Paul Verhoeven's "Starship Troopers" make ample use of this idea: http://www.youtube.com/watch?v=x7-PQIuWwLo http://www.youtube.com/watch?v=x7-PQIuWwLo
bitwize 15y ago
It seems you and Heinlein are of like mind; remember Mycroft's conclusion in The Moon is a Harsh Mistress that the best way to fight the Earthen forces was to "throw rocks at them"?
cpeterso 15y ago
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.

makmanalp 15y ago

Ender's game spoiler alert! Hope it doesn't ruin it for anyone else... (grumble.) Anyway, how the heck does one lob a comet? If throwing one was so easy, why wouldn't they just throw it right back at you?

quanticle 15y ago
Well, both gwern's essay and the essay linked by OP assume that both sides have ships capable of interstellar travel. In gwern's case the idea is to not bother with the ship; just bolt an interstellar drive to a comet and point it at the enemy's homeworld. As for them throwing comets back at you, that is addressed in the essay. In short, there is nothing stopping them from throwing comets back. Space war will resemble the Cold War much more than any active engagement. Mutually assured destruction will be the overriding doctrine.
aaronblohowiak 15y ago
Do you really need a spoiler alert on a young-adult novel that has been out for 26 years?
- blake8086 15y ago
  It's not like they stopped making young adults 26 years ago.
patio11 15y ago
Physics. Attacker gets arbitrary mass (reactant, etc) and time to accelerate. Defender needs same mass/time to decelerate... after discovering the attack. Note that you could literally prep an attack for millennia which would be discovered a matter of hours prior to ending a civilization. Physics makes for sucky narratives. Good thing it also makes for a vast, dead, boring universe.
- Tichy 15y ago
  I don't think you would try to slow down approaching meteorites to zero speed, only deflect them a little so that they miss the planet. The further away you catch it, the less energy it takes (I assume, didn't do the maths).
  - kbolino 15y ago
    Debatable. On the one hand, the farther the projectile is from the planet, the less it needs to be deflected. On the other hand, you have to expend energy to get to the damn thing in the first place. I suppose the survival of your species renders moot most energy concerns though.
  - quanticle 15y ago
    It depends on the momentum of the asteroid. If I've accelerated an asteroid up to .5c, then even if you discover the attack years ahead of time you might still not have the energy to deflect the asteroid by enough to save your planet. You also have to remember that the attacker can launch multiple simultaneous asteroids. You might have enough nukes to deflect one asteroid. Do you have enough to deflect ten? A hundred?
    - russell 15y ago
      If you can accelerate an asteroid up to .5c, you have harnessed energy resources to power the earth for a gazillion years. You would be so rich that you dont need to be a warlord. You could become ... a banker. Actually, at .5c from the Kuiper belt, the warning time is only 30 hours or so and the momentum is such that deflection is impossible. I'm too lazy to do the math but the collision would be spectacular.
    - nialo 15y ago
      Momentum doesn't really work this way. The only things that change the difficulty of deflecting something are it's mass, and the remaining time to impact. Having a lot of momentum doesn't change how much force is required to give something a given acceleration until relativistic effects start to matter. (I guess distance also makes it harder, because you need to travel further to start deflection, but that's not really a momentum thing)
talmand 15y ago
Spoils Ender's Game? Bummer. I recommend you read it anyway.

meric 15y ago

I postered a comment on the essay, I'll repost it here: You assume the interstellar species will be living on a planet. What if they hollowed out their planet of resources long ago and now live in a cloud of asteroids instead? Asteroids are hollowed out as giant fortresses in space, and a bio dome sphere thingy built inside. As they are living in an asteroid cloud, to prevent impact they would have to attach thrusters to each asteroid they live on to dodge other asteroids. So the asteroid from kuiper belt attack won't work... but what if the asteroid was launched at close to speed of light? 1. That would take a very big amount of energy. 2. They would've had to carry the energy to the kuiper belt. 3. They would've been noticed and a fleet would've sent in to capture it before the asteroid was launched. What about the nuclear bomb? Well they live deep in the asteroid, it'll protect at least against some nuclear hits. If one asteroid blows up there are still 499 others. Still it would be great to prevent the loss of sentient life... Also what happens if 500 nukes were launched at each asteroid? I've got no answer to that. I do wonder if there could be a device that would force nuclear explosives to be triggered prematurely, lets say, 2km away. That would be sufficient to protect the asteroid.

quanticle 15y ago
What about a shotgun approach? Take a comet, accelerate it up to a significant fraction of lightspeed (after all, you you have lightyears in which to do so), and trigger a bomb in the comet to blow it apart into a few smaller pieces, each traveling at a significant fraction of c. Rinse and repeat.
- 46Bit 15y ago
  That's probably the best suggestion here. Not as easy to deflect something like that.
- meric 15y ago
  I've made another reply at the site: So the invading force goes into the Oort cloud, picks a chunky rock, attaches a giant thruster to it and begins accelerating it towards c. A day later, the speed of the rock has reached 0.5c. Hours later, a defending fleet arrives, shoots and kills all the invading bds. The rock however, continues at 0.5c even though the thruster and guidance systems were destroyed. It reaches the asteroid cluster, and hits... nothing. It keeps going to the other side of the solar system, and as its speed was so high, exits orbit. Accelerating a giant rock to c takes throwing out alot* of gas. The asteroid based civilisation, to prevent random impacts with random asteroids, would've been tracking every object in the belt. One of the rocks suddenly accelerates, I think it will be picked up. Also, when the asteroid was accelerating, its direction would've been picked up. Once accelerated to c, it will still take hours to arrive at the designated target. The home asteroids simply have to maneuvre away from an intercept course. And no, guidance systems on the accelerated rock won't help. It's travelling at c, and by the time the system finds out the target has moved away, the asteroid would've missed it. Unless the asteroid have 100% maneuverability, and energy to change course whenever, however it likes. But if the asteroid can do that, any asteroid can do that. ;) So your only option is accelerating the rock from the next system onwards. It will now take years for the asteroid to arrive. To reduce the probability of a successful attack, just have a "random thruster day" every 30 days where all the home asteroids just move randomly to different locations. By the time the enemy asteroid arrives the location of all the home asteroids would've been different. The probability of hitting anything worth hitting will be very low. Even if you have 1000 incoming asteroids. Also you're assuming you won't get picked up accelerating an asteroid to c in the next system; Remember, asteroids have no atmosphere and 100% visibility. You might miss 1, but 1000? I'd doubt it. if 1000 asteroids are really incoming then you just make every day random thruster day. ;) They have so much energy, you should too.

zeteo 15y ago

The fighting methods in that essay still require ships (to sneak up into e.g. Kuiper's Belt). In any case, a big, dumb projectile can have its course changed with much less energy than required to fire it. The bigger it is, the earlier it will be detected; and the faster it goes, the smaller the angular deflection needed to miss its target.

pilom 15y ago
While it is true that it should be easy to deflect, it is only easy to deflect if you can detect it. The essay assumes that the projectiles would be pushed to a significant fraction of the speed of light. At that speed there is no time to launch any type of deflection.
- zeteo 15y ago
  The energy required to accelerate a big object to even half the speed of light is prohibitive. Even if the process was feasible, it would be a vast cosmic event bound to emit some radiation, which would still arrive much sooner than the object itself.
  - quanticle 15y ago
    Well you don't have to accelerate it all at once. Remember, this is space war, and we're playing for keeps. Spending a millennium to accelerate a rock up to .5c might be worth the trouble.
    - zeteo 15y ago
      If you take longer to accelerate it, that just increases the probability of detection by other means. It still doesn't change the argument that it should be much cheaper for the defender to detect and deflect your projectile than it was for you to launch it in the first place. Not to mention that an unmapped interstellar gas cloud, or an undetectable asteroid, is all it takes to deflect the projectile a few millionths of an arcsecond and make it miss its target.
15y ago

dhs 15y ago

The "bugs" in Paul Verhoeven's "Starship Troopers" make ample use of this idea: http://www.youtube.com/watch?v=x7-PQIuWwLo http://www.youtube.com/watch?v=x7-PQIuWwLo

bitwize 15y ago

It seems you and Heinlein are of like mind; remember Mycroft's conclusion in The Moon is a Harsh Mistress that the best way to fight the Earthen forces was to "throw rocks at them"?

cpeterso 15y ago

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.