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[li]The ability to voyage between stars, even if done with some kind of speculative superluminal or nonlocal path propulsion implies the ability to construct and manage large structures in space, which also implies the ability to mine resources and be self-sufficient in basic needs (food, water, air). You’re not going to develop a space-going population by lugging stuff up against Earth’s gravity. Once you have the ability to do so the necessity of a planetary surface is much reduced; basically, the only things a planet uniquely provides is gravity (which can be simulated by rotating a body about an axis), and radiation shielding (accomodated by adding dense, impermeable mass to the outside of your habitat/ship). [/li][/QUOTE]
The tricky part here is food. Raw materials, water, even air can be found at various places in space (presumably a planet or moon might have more of them to be found, depending on the planet. I imagine Europa probably has plenty of water to be found, if Arthur C. Clarke wasn’t pulling my leg.
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[li]Habitats, like planets, can do just fine orbiting around a star, and indeed, if you’ve the ability to sustainably generate power independant of a star, there’s no reason why you couldn’t just survive indefinitely in deep space.[/ol] [/li][/QUOTE]
Problem is still building them without an existing anchor. If you get the velocities right, you can use a star for an anchor, but then you still have to haul all your supplies from wherever you’re getting them, when it might be easier to just drop them on the planet until they’re needed, or even get them produced on the planet where possible.
But yeah, back to the topic of how to invade the planet rather than why you’re doing so, I figure that a big problem would be protecting whatever troop transports or supply ships you have until the defenses are neutralized, and making sure they don’t have some lying in wait for the landing craft to get close enough. Also, if you want to land a large force, it might be best to find a relatively out of the way spot on the planet to land on and mass your forces at before you take on the locals. Landing craft diving in near the enemy’s center of power would be a lot more vulnerable than landing craft landing in a desert somewhere on the other side of the planet (in the case of planets that aren’t necessarily teeming with populations, like, say, colonies or some such.)
It’s quite possible that in whatever universe you are in, it is much easier to make ground-to-space weapons than vice versa – after all, on a planet you are not limited to things you can get into space, so defensive weapons could potentially be huge. Things you’d have to remove by either a (or several) fusion strikes or a precision demolition invasion by trained rangers/marines. And if there are enough of them you’d have to take out most of the populace to nuke 'em from orbit. Drop a small force in secret or concentrate enough firepower to temporarily silence the PDL’s wherever you are attacking.
And on the flip side of the coin, ground based weapons can be small. Heck, we have truck-based nuclear missiles – with just a bit more propellant oomph and a better bomb, you’d have a truck-mobile spaceship killing machine. Potentially thousands of them scattered across the globe, who knows exactly where. (Sure, space fighters could also use these, but we want the population intact.)
Onto the OP: how to successfully invade a planet? If it’s human, precision-strike to take out the government and communications. Then you could forseeably take out the remaining resistance in a piecemeal fashion.
And as to non-humans, most space-faring species have something resembling a “goverment” and “communications”, so concentrate on those (hive queens, central computers, etc.) Although depending on the exact culture of the aliens they might be so fanatical that they would not be able to control without killing them (humans too, for that matter.)
Can a fleet of ships pack enough whoop-ass to overcome and entire planet’s worth of whoop-ass? Would any valuable planet be defenseless?
How much ‘intact’ do we want the planet? Can we wipe all the Things From Another World as long as we leave the geography intact? That would seem to indicate a biological attack would fill the bill.
Do we want to enslave the population? If so, that would require a large bucket filled with cultural information.
If we want to preserve the geology only, just nuke them from orbit. It is the only way to be sure.
In StarShip Troopers, they weren’t just attacking ‘willy-nilly’, nor were they attempting to invade the planet. The Troopers were demonstrating that we had the potential to have nuked them from orbit but chose not to. They went in on surgical strike missions where they did as much ‘small’ damage as possible, blowing up installations, important buildings, terrorizing the inhabitants, etc. This action convinced the planetary government that it was in their best interests to join our side instead of fighting us. (when fighting the ‘skinnies’, things were different when fighting the bugs) When fighting the bugs, they originally went in to hold ground when they thought the bugs were not intelligent, and then to gather intelligence once they learned otherwise. Intelligence gathering is not something that can be done from space.
Remember that Heinlein (for all his vision) hadn’t thought it possible to build guided missles that could be used in the same way to hit specific targets. He thought the only other option was mass destruction like a nuke, and that would have been overkill.
Given your qualifications, clearly the first order of business is taking out their space force and any orbiting or satelite defences. Once you control the high ground it is relatively easy to take out all other fixed planetary defenses and military installations.
Then once the defenders are forced to rely on small mobile defenses and scattered forces, it is possible to threaten the cities with destruction with examples of a few strategic strikes on utilities or historical sites to prove your power and ability. The local government should be forced to surrender. If they don’t then you carry out your threats and ask again making it clear that it’s your final offer. (and if the idea of nuking millions of inhabitants to make good your threats makes you uncomfortable, you shouldn’t be in the business of invading other planets… )
I agree, we’re going to need a LOT more info to determine strategy. You’d attack an alien hive-mind society a lot differently than you’d attack a human democracy, for instance.
If, as stipulated by the OP, your objective is to control the surfaces and its resources and not to wreak TOO much havoc, there’s something to be said for seizing and controlling whatever indig pooh-bah is in charge. Cortes in Aztec Mexico, Pizarro in Inca Peru, and MacArthur in post-WW2 Japan did that with some success (not unlimited in the first two examples, I’ll concede). Particularly if the indig society is feudal or otherwise highly respectful of authority, having the Top Dude under your thumb - and well-protected against assassination or being deposed - leaves you sitting pretty. You can issue orders through your puppet (being careful not to be TOO overbearing or obvious in your pulling of the strings), and get what you need without nuking from orbit or otherwise laying (counterproductive) waste.
You’re positing mankind as capable of travelling interstellar distances; clearly, they’ve already mastered the technology to generate large amounts of power in space.
Again, any given world, even one in an Earth-like orbit about a suitable star, is unlikely to be able to sustain agriculture and animal ranching without dramatic modification. Unless the planet has natively develped oxygen-based life, it will almost certainly have a reducing atmosphere, as free oxygen in absense of a seperation mechanism will tend to reduce just about any simple compound.
Native life, should it exist, is manifestly unlikely to provide nutrition to H. sapiens. The construction of complex proteins is largely arbitrary; that is to say, they’re formed the way they are because they fit into their complementary receptors. Basic compounds–like hydrochloric acid, or calcium carbonate–and possibly some of the essential amino acids will be universal, but it’s extremely unlikely that any nonterrestrial life will produce, say, Vitamin C or any of the carbohydrates we require.
This attitude is, if you’re excuse my neologism, a very gravi-centered viewpoint. If you have a permanent spacefaring species (and if your conjecture involves a species capable of interstellar travel you’ve virtually accepted that premise) then they needn’t orbit any “anchor”. If they choose to, for the purpose of maintaining a determinate position about a quasi-fixed mass, it would certainly be no great effort for such a force to place their ships/habitats/power sources/communications equipment/farm enclosures (assuming they don’t just synthesize their food)/et cetera in orbit about a star or any random planet. Hauling stuff, be it food, minerals, or fuel, up from the surface of a planet would be foolishness; sending it down to a planet is nearly as bad. Either you have to cope with slowing it to surface rotational speed, send it screaming through the atmosphere and protected it as best you can from heating, or build enormous elevators to send stuff up and down safely and efficiently. All of these are steps an emergent space-faring species might do, but one capable of moving between stars is hardly going to be bothered with the needless effort to yank stuff up and protect it going down into a massive gravity well, much less fight over said planet. That most interstellar science fiction is predicated on the notion that humans will be living and fighting over planets just serves to illustrate that the authors of such are looking more toward Louis L’Amour and C.S. Forrester than Buckminster Fuller or John von Neumann. Star Wars is The Hidden Fortress plus The Guns of Navarone in space. Star Trek was pitched as Wagon Train across the galaxy.
We might still enjoy and visit planets for their esthetic value, but it hardly makes sense for a spacefaring species to base its operations on one, much less fight over it. To paraphrase George S. Patton, planetary fortifications are a monument to the stupidity of man.
That being said, if you were a sufficiently advanced race capable of interstellar travel and wanted to choke a world into submission, I’d pulverize a few large asteroids/moons/wandering star goats into a light dust and ash and dump it into the planet’s atmosphere. For extra fun, you can activate it by spraying it with neutrons and and creating a lot of radioactive isotopes. Between the suspended dust and the cloud cover that would nucleate you’d kill off the photosynthetic life and by extension the mass of large indigenous lifeforms, including, presumably, the dominant race you wished to eradicate. You need not even get close to the planet; just send your dust cloud into an near-equivilent velocity intercept orbit and come back in ten years or so. It’s much easier than fussing about with all those R26c Pumped Meson X-Ray Lasers and M241 Phased Plasma Cannons and Antimatter-Triggered Gravi-Flux Air Incenertor Bombs and all that crap that never works like Tom Clancy IX describes in his Sens-O-Novels anyway, plus you don’t need to dig up and haul around a bunch of no-neck space marines who are just going to get bored on the trip and beat the shit out of each other or vandalize your ship. And you can save your warbot-fabrication facilities for manufacturing pleasure units instead.