Alien Invasions

[Flyndaran]

Originally Posted by David Johnston2

The reasons why someone invades

1. Vikings. Vikings just show up in small numbers to raid and loot. They're here to steal our plutonium, or refined petrochemicals, or tobacco, or human or bovine DNA. They snatch and grab because it's easier than trading and safer than conquest. Either the locals can pose a threat if you give them a chance to mobilize everything they've got or there's an outside force that will intervene if you hang around. Or maybe they just don't like the climate.

2. Merchants. Merchants actually just wanted to trade. We have something they want, maybe bananas or spinal cords, and they can get huge amounts of it exchange for what they think of as trinkets. So they set up a trading outpost and things go smoothly for a time. But then politics happens. Terrorists attack them, or the local government destabilizes or a war breaks out and...suddenly...they have money in the game. Their representatives and their financial interests are being threatened and now it's time to call in their military or mercenaries to establish some order...

3. Imperialists. Imperialists are just looking to fill space in their map. They can move in and take over pretty easily, establishing a puppet government and paying for the expense of the operation by taxing their new subjects. They'll try to modernize their new acquisition a bit so it can pay more taxes.

4. Farmers. Ah...farmers are bad. They have no interest in us or the things we produce or can produce. They just happen to be pretty perfectly suited to live here (or will be once they fix things up a bit) and there aren't all that many places out there that fit that bill. So for them we're just the vermin that needed to be cleared away, exterminated, enslaved or at best confined to "reservations" set up on land they don't find of much value.

6. Converts to their religion/lack of religion/philosophy/right way of thinking.

7. Research. They always thoroughly study the biosphere of alien worlds especially any sapients they find. Perhaps they want to go "Borg" and copy beneficial traits.
Or just want to catalogue everything even if it destroys ecosystems in the process. It's all just information, right? They can always recreate life from data if they need to.

[Daigoro]

Originally Posted by AlexanderHowl

They do not necessarily need a planet, but why would you not put your base in orbit around Saturn?

I have no argument with putting a military base on Saturn. I was talking about your assertion that invading forces would have to jump in within 0.5 AU. Why is that so? Saturn is located at just one point on a 10 AU diameter sphere of exclusion.

[AlexanderHowl]

They could jump in anywhere outside of the exclusion zone. If they jumped any further than 0.5 AU from Saturn, they only increase the warning that the forces at Saturn have. Of course, they could jump in, dive 6 AU to attack a Main Belt installation, but the force based at Saturn would be able to catch up with them before they could exit the exclusion zone, so it would not be the best tactical choice.

[Daigoro]

Originally Posted by AlexanderHowl

They could jump in anywhere outside of the exclusion zone. If they jumped any further than 0.5 AU from Saturn, they only increase the warning that the forces at Saturn have. Of course, they could jump in, dive 6 AU to attack a Main Belt installation, but the force based at Saturn would be able to catch up with them before they could exit the exclusion zone, so it would not be the best tactical choice.

What if they're in opposition?
Saturn is at 12 o'clock, and this Main Belt target is at 6 o'clock.
The invaders have 6 AU to cover from the edge of the exclusion zone, while the Saturn defenders have 14 AU to traverse. How would the defenders be at an advantage?

[AlexanderHowl]

So, let us say that the attackers come into the system at 3g (we will assume no retention of velocity after a hyperspace jump in this setting to make things easier). It takes them 2 days to reach turn around and 2 days to stop (they can run back in 3 days because they do not have to slow down to jump). Even at opposition, the Imperial Fleet at Saturn can intercept the enemy vessel in 4.5 days at 3g because they do not have to slow down.

The enemy will be two days from being able to jump no matter which way they run when the Imperial Fleet catches up to them. Now, the Imperial fleet will only get one turn of engagement because they will be going .04c but that just means that the missiles will utterly destroy anything they hit. I do not think they will even send the big guns, as a dozen SM+8 cutters will have more than enough firepower at that velocity to destroy any capital spacecraft.

[Daigoro]

Still don't see how 0.5 AU falls out of that.

And that scenario grants the attackers 12 hours to wreak havoc at will on their target. If you're giving the defenders perfect one-shot missiles, the attackers would have the same, so 12 hours would be quite sufficient. Furthermore, if the defenders don't have to slow down to engage, then neither would the attackers. They could strafe their target and be back outside the 10 AU well before they're intercepted if they don't decelerate.

And, this all supposes that the defenders have perfect detection as well.

[dcarson]

A. E. Van Vogt had a interesting invasion scenario, seizing a planet was legal in the sense that no one will try and stop you but killing too many locals was genocide which would cause other powers to intervene. So you need to hold back on how much force you use.

[Flyndaran]

That also reminds me of the original V, or at least from what my foggy memory recalls. The invaders were led by someone trying to gain political power with methods that would not have been sanctioned by the distant rulers.

A full out genocide would have been impossible to sweep under the rug or perhaps incite a more expansive mutiny.

[AlexanderHowl]

Originally Posted by Daigoro

Still don't see how 0.5 AU falls out of that.

And that scenario grants the attackers 12 hours to wreak havoc at will on their target. If you're giving the defenders perfect one-shot missiles, the attackers would have the same, so 12 hours would be quite sufficient. Furthermore, if the defenders don't have to slow down to engage, then neither would the attackers. They could strafe their target and be back outside the 10 AU well before they're intercepted if they don't decelerate.

And, this all supposes that the defenders have perfect detection as well.

Perfect detection is assumed when you have SM+14 objects exiting hyperspace (a TL10 SM+14 spacecraft with an enhanced array would have a -3 to skill to detect the attackers every turn at 20 AU). If the attackers do not decelerate, they will have their own issues when they engage the defenses of the mining facilities. If the attackers do not start delegating at 1 AU from the asteroids, the mining facilities can just toss out gravel and laugh when the enemy hits a cloud of gravel at 0.02c (a one gram speck of gravel would have the effective energy of 9 metric tons of TNT).

Since hyperspace capable spacecraft in the setting have to possess a minimum mass of one million metric tons, they possess a very large crosssection, around 10,000 square meters at a minimum. A gravel cloud with a mass of 10,000 metric tons and a density of 1 kilogram per cubic kilometer could defend 10 million cubic kilometers of volume. It would be a quite effective defense.

[Boomerang]

Here is another alternative. Or perhaps an addition to the Saturn idea.

Around 100 million years ago an intelligent race evolved from dinosaurs and achieved TL9 technology thousands of years later. They sent a fleet of generational ships to a distant star, meanwhile back on Earth their technology stagnated at TL9. At some point their civilisation imploded and the generational ships lost contact with their home world. Over millions of years the evidence of their advanced civilisation was lost, buried deep below the Earth’s surface. The new colony on a distant planet eventually lost all knowledge of Earth.

Millions of years later radio signals are intercepted by remote sensing stations on the border of the new galactic empire. A ship is dispatched to investigate and is astounded to find that the natives on this planet now called Earth have a common genetic ancestry with the citizens of the galactic empire.