Alien invasion scenario's.

[primummobile]

The best kind of beamed propulsion method I've read of is the 'smart particle' method; instead of using light you use tiny pellets with some kind of steering mechanism that can home in on the spaceship to transfer their momentum. Jordin Kare came up with a scheme to accelerate ships using tiny foil light sails accelerated by lasers, which have little guidance systems on-board and can be programmed to converge on the ship even if it is outside the distance at which a laser can be focused. Of course such mass-pellets would make a good weapon, but so would any conceivable method of interstellar transport.

Are you talking about this?

http://www.niac.usra.edu/files/studi...rt/597Kare.pdf

[eburacum45]

Are you talking about this?

http://www.niac.usra.edu/files/studi...rt/597Kare.pdf

That's the one. Kare suggests that a magbrake might be useful for deceleration on arrival, but this method is most efficient when decelerating from high speeds to moderately high speeds; to slow down to orbital speeds would requite something else.

[Noclevername]

That's the one. Kare suggests that a magbrake might be useful for deceleration on arrival, but this method is most efficient when decelerating from high speeds to moderately high speeds; to slow down to orbital speeds would requite something else.

Maybe send another swarm of projectiles ahead and swing them around the target star to intercept the incoming probe/ship? (It would require a long lead time and projectiles that were very easy to decellerate.)

For that matter, why not use the projectiles as a probe? They'd have to be fairly smart to find their target, add some small sensors and you've got a compund eye of sorts.

[eburacum45]

Isaac Kuo (of this forum) another idea which might work better. If the projectiles from the home system can be made to collide in front of the ship they will explode isometrically and provide a significant braking force to the ship itself. This obviously presents some design problems but it might be easier to arrange than swinging projectiles around a star.

[Ara Pacis]

Isaac Kuo (of this forum) another idea which might work better. If the projectiles from the home system can be made to collide in front of the ship they will explode isometrically and provide a significant braking force to the ship itself. This obviously presents some design problems but it might be easier to arrange than swinging projectiles around a star.

Or if the projectiles were sent ahead of the ship in a slower trajectory instead of a faster one, the speeded-up ship could catch them and then use a mass accelerator to push them in the other direction to reverse thrust.

[eburacum45]

Or if the projectiles were sent ahead of the ship in a slower trajectory instead of a faster one, the speeded-up ship could catch them and then use a mass accelerator to push them in the other direction to reverse thrust.

Yes; I would call this a 'prepared track' strategy - you start sending out projectiles long before the main ship is launched, maybe hundreds or thousands of years before, so that they are in place for deceleration. This sort of strategy highlights the need for long periods of singleminded dedication that could enable interstellar colonisation in the very long term. Not many people or organisations in today's society would be content to devote much time to such long term aims, unfortunately.

[Noclevername]

Not many people or organisations in today's society would be content to devote much time to such long term aims, unfortunately.

Not us (yet), but a post-senescence society would have plenty of time.

[Noclevername]

OTOH, religions have dedicated generations to building a cathedral in Dark Age Europe, so we know humans can do longterm projects-- we just aren't in that mindset presently.

[headrush]

Going back to the "aliens harvesting minerals from parts of the solar system and just ignoring us" idea.
I would imagine that the detection of such aliens so close to us would cause some pretty frantic military activity here on earth. I'd also imagine that funding would become available for many more deep space projects, perhaps leading to manned colonies in the asteroid belt and beyond.

My reasoning for the last point is thus. If we were to try to defend the inner solar system we could not rely on remotely operated drones, the time lag makes them impractical to operate effectively. So manned stations amongst the asteroids could more directly control the attack drones. There would still be no real need for manned x-wing fighters, more's the pity.

[Noclevername]

Going back to the "aliens harvesting minerals from parts of the solar system and just ignoring us" idea.
I would imagine that the detection of such aliens so close to us would cause some pretty frantic military activity here on earth. I'd also imagine that funding would become available for many more deep space projects, perhaps leading to manned colonies in the asteroid belt and beyond.

My reasoning for the last point is thus. If we were to try to defend the inner solar system we could not rely on remotely operated drones, the time lag makes them impractical to operate effectively. So manned stations amongst the asteroids could more directly control the attack drones. There would still be no real need for manned x-wing fighters, more's the pity.

Nothing would get us off our butts and into space like an unknown, potentially dangerous threat right in our own neighborhood. We'd likely have defenses in depth, in case the aliens might decide to lob asteroids our way.

[swampyankee]

Nothing would get us off our butts and into space like an unknown, potentially dangerous threat right in our own neighborhood. We'd likely have defenses in depth, in case the aliens might decide to lob asteroids our way.

Using our history as an analogy, at least some countries would quite cheerfully work with the aliens to improve their relative position. It happened during the conquest of the Americas, the British conquest of India, the British and American conquests of North America, and the African slave trade. This may be much more of a threat than the aliens themselves.

[Noclevername]

Using our history as an analogy, at least some countries would quite cheerfully work with the aliens to improve their relative position. It happened during the conquest of the Americas, the British conquest of India, the British and American conquests of North America, and the African slave trade. This may be much more of a threat than the aliens themselves.

That's assuming the aliens work with or even communicate with us.

[Colin Robinson]

Using our history as an analogy, at least some countries would quite cheerfully work with the aliens to improve their relative position. It happened during the conquest of the Americas, the British conquest of India, the British and American conquests of North America, and the African slave trade. This may be much more of a threat than the aliens themselves.

Another historical analogy (which Chris Boyce mentions in his book Extraterrestrial Encounter) is the contrast between Herodians and Zealots of Judea, at the time of the Roman Empire. The Herodians cheerfully worked with the Romans, the Zealots thought death preferable to Roman rule...

Fictional portrayals of alien invasions tend to have Zealot-like heroes -- brave warriors fighting for planetary freedom against overwhelming odds, like the warship Thunderchild in H.G.Wells War of the Worlds.

An exception is Arthur C. Clarke's novel Childhood's End. In that novel (for those who don't know) the aliens arrive openly, parking huge space craft in an orbit directly over each of Earth's greatest cities. They then contact Earth by radio, and announce in quite a diplomatic way that the planet is now under their overall protection, but they have no intention of displacing existing local authorities and institutions. Looking at the unknown, but clearly very advanced technology of the huge space craft, most of Earth's governments reach the conclusion that resistance is futile. One state makes an attempt to nuke an alien craft, only to find it doesn't work...

So then the whole planet basically goes Herodian.

What else would you do?

[Solfe]

I am working on a story where the Earth is invaded as the only known source of vacuum tubes. This precludes blasting us from orbit, tubes are fragile.

Obvious this is comedy, but I was thinking of how to conduct and repel a proper space invasion.

If you are an alien that does not want to be exposed to our atmosphere, you do not want the hairless apes firing machine guns and throwing bottles of flammable liquids on your cool power armor. Something will give eventually. How tough could power armor be? Could you have troops that could take a hit from a tank or missile? Is there a practical upper limit to how much armor is actually useful?

High tech Earthly weapons may be subject to jamming or worse, infection or subversion by a superior Alien tech. Nuking stuff in orbit would not be a good idea for humans, we would lose our technology in the attack. If nukes are off the table, exactly how many of those missiles can be fitted with conventional explosives? How many "test flights" would be needed to hit something? If you have a few thousand launchers, how annoying would dozens or hundreds of test flights be for the orbiting attackers? Imagine that no human Alliance was made and the owners of such weapons where all working independently. That would be messy and disordered to say the least.

The Alien force would have to establish beachheads some place so they don't have fly home to orbit after an attack. How would humans dislodge an beachhead in Antarctica or some other difficult Earthly environment? More annoying, what if the beachhead was a park in a large city, like Central Park. Assume the Aliens aren't attacking the citizens, that would be a major headache for military planners. How long would the Aliens be able to conduct operations before having to be resupplied?

I am trying to think of the other silly scenarios breaking ideas.

[Paul Wally]

I am working on a story where the Earth is invaded as the only known source of vacuum tubes. This precludes blasting us from orbit, tubes are fragile.

Obvious this is comedy, but I was thinking of how to conduct and repel a proper space invasion.

If you are an alien that does not want to be exposed to our atmosphere, you do not want the hairless apes firing machine guns and throwing bottles of flammable liquids on your cool power armor. Something will give eventually. How tough could power armor be? Could you have troops that could take a hit from a tank or missile? Is there a practical upper limit to how much armor is actually useful?

High tech Earthly weapons may be subject to jamming or worse, infection or subversion by a superior Alien tech. Nuking stuff in orbit would not be a good idea for humans, we would lose our technology in the attack. If nukes are off the table, exactly how many of those missiles can be fitted with conventional explosives? How many "test flights" would be needed to hit something? If you have a few thousand launchers, how annoying would dozens or hundreds of test flights be for the orbiting attackers? Imagine that no human Alliance was made and the owners of such weapons where all working independently. That would be messy and disordered to say the least.

The Alien force would have to establish beachheads some place so they don't have fly home to orbit after an attack. How would humans dislodge an beachhead in Antarctica or some other difficult Earthly environment? More annoying, what if the beachhead was a park in a large city, like Central Park. Assume the Aliens aren't attacking the citizens, that would be a major headache for military planners. How long would the Aliens be able to conduct operations before having to be resupplied?

I am trying to think of the other silly scenarios breaking ideas.

Why don't they just ask for it? We're using transistors these days

[primummobile]

Why don't they just ask for it? We're using transistors these days

And if they need a bunch of vacuum tubes, then think of all the jobs they'll bring with them.

[Solfe]

Why don't they just ask for it? We're using transistors these days

Its a lifestyle choice. Transistors don't have that warm glow. : )

[swampyankee]

Gee, it would be so much easier to make vacuum tubes in space. No need for vacuum pumps!

[IsaacKuo]

Gee, it would be so much easier to make vacuum tubes in space. No need for vacuum pumps!

Obviously that's the reason why Earth is the only known source for vacuum tubes. Every other technological species went spacefaring before inventing electronics, so none of them ever invented vacuum tubes.

[Noclevername]

Gee, it would be so much easier to make vacuum tubes in space. No need for vacuum pumps!

They don't have glassmaking technology. To see outside the ship they have to open the door and glance out quickly. It makes landings difficult, as you can imagine.

[IsaacKuo]

Or if the projectiles were sent ahead of the ship in a slower trajectory instead of a faster one, the speeded-up ship could catch them and then use a mass accelerator to push them in the other direction to reverse thrust.

This only works down to the speed of the slower projectiles, which must still be a large fraction of c if you want to get anywhere at a decent speed.

I have been working on a few other things lately, but I will return to working on relativistic kinetic impact powered rocket concepts for interstellar propulsion someday. It's suitable for propulsion for a return journey as well as for braking. That makes kinetic impact powered rockets a serious option for a manned return mission to another star system.

[Solfe]

More insulting Alien Tech: "We managed to get here at .09108587345 c. We were kind of expecting you to be extinct by now. We can wait."

[swampyankee]

More insulting Alien Tech: "We managed to get here at .09108587345 c. We were kind of expecting you to be extinct by now. We can wait."

or ...."We can help."

[Noclevername]

I've read at least two unrelated SF stories about aliens who invaded because they'd seen our alien-invasion movies, and thought that was our preferred method of first contact.

[swampyankee]

They don't have glassmaking technology. To see outside the ship they have to open the door and glance out quickly. It makes landings difficult, as you can imagine.

Maybe they should try a screen door, plus it'd keep the meteorites out =8-)

[Noclevername]

Maybe they should try a screen door, plus it'd keep the meteorites out =8-)

They'd have to strip them all off their submarines!

[swampyankee]

They'd have to strip them all off their submarines!

That's because they discovered the Daleth Effect, and their space ships are modified submarines.

[KaiYeves]

Its a lifestyle choice. Transistors don't have that warm glow. : )

So the aliens are hipsters?

[Solfe]

I've read at least two unrelated SF stories about aliens who invaded because they'd seen our alien-invasion movies, and thought that was our preferred method of first contact.

In the David Brin's Uplift series, humans have almost no technology but the two things they excel at are special effects and communications. They use both to good effect tricking the enemy into doing things.

[Noclevername]

Another historical analogy (which Chris Boyce mentions in his book Extraterrestrial Encounter) is the contrast between Herodians and Zealots of Judea, at the time of the Roman Empire. The Herodians cheerfully worked with the Romans, the Zealots thought death preferable to Roman rule...

Fictional portrayals of alien invasions tend to have Zealot-like heroes -- brave warriors fighting for planetary freedom against overwhelming odds, like the warship Thunderchild in H.G.Wells War of the Worlds.

An exception is Arthur C. Clarke's novel Childhood's End. In that novel (for those who don't know) the aliens arrive openly, parking huge space craft in an orbit directly over each of Earth's greatest cities. They then contact Earth by radio, and announce in quite a diplomatic way that the planet is now under their overall protection, but they have no intention of displacing existing local authorities and institutions. Looking at the unknown, but clearly very advanced technology of the huge space craft, most of Earth's governments reach the conclusion that resistance is futile. One state makes an attempt to nuke an alien craft, only to find it doesn't work...

So then the whole planet basically goes Herodian.

What else would you do?

Given that any practical interstellar drive is also a weapon, that actually seems like the most reasonable way for aliens to take over; maybe blow a few new craters into the Moon or destroy Pluto* or something as a demonstration, then park over a few national capitals and say "get the message?"

*Poor pluto always gets it in the neck! Not only is it demoted, it's also the most-destroyed non-Earth world in all of science fiction!