Hundreds of Billions?
Yeah, no.
Unless said planet is the size of Jupiter or Saturn (which is completely impossible unless you bring out Hand Waves and Applied Phlebotinum) An invasion force in the 12 digit range is the definition of Over Kill.
Planets are "huge" relatively. But you're really overestimating its size.
New Survey coming this weekend!No we have it very much right. You can't land if you can't make it through the orbitals or linger in orbit long enough to send troops to the surface in numbers large enough to matter. If every time you approach an orbit something twats the ship you can't land forces or land forces in numbers to halt the equivalent of an entire highly developed planets worth of potential military power. It is as simple as that. Societies that can send things like armadas across the depths of space would have no trouble providing defense in depth of a developed planet in the orbital bands or fielding very large military bodies with the resource of an entire planet. They could also easily place things on the surface that can fire into orbit with a nice advantage on their end of having a nice clear view of everything in orbit. There is no where to hide in orbit. So you better make sure nothing can shoot at you if you are going to linger in orbit.
The large number of troops required has nothing to do with defending every square inch at all. It has everything to do with the number of people it takes to take control of large regions. You are talking about conquering an entire planet. The size of armies required to do that for large nations number in the millions. You start talking about taking urban environments especially heavily built up areas that number of troops goes up a lot.
That isn't accounting for the fact both populace and other groups could choose to wage a long drawn out guerilla war. Heavily lived on and settled planets are likely to have a lot of civilization everywhere and with that a lot of possible military presence everywhere. As of right now just 17 nations on a non-total war footing provide 50,951,813 in military troops including all support and reserve personnel and all the equipment and bases that possibly entails. If we divided that number alone evenly to all the continents of the world each continent could have a standing military of over 7 million apiece.
Take a reasonably united world put it on a war footing with a total war mindset and you can have massive armies guarding each major continent. You are not going to take that easily. Even on a non-war footing at 7 million per continent you are going to need overwhelming force to defeat that kind of military might. That is with just 17 nations with militaries with over a 1 million troops total now. The number that have under that would swell the number to an army that possibly numbers over a billion. We are talking about a conflict where the resources of an entire world are being pitted against an invading armada.
You could easily put hundreds or even thousands of land based systems alone that could loft munitions into various levels of orbit. Right now there are sea based missiles that can reach into roughly the middle band of low orbit alone.
That is just with stuff now. We are talking FTL societies chances are pretty good they can project fire power a lot further though speed of a projectile is still an issue.
Before you can park in LEO and send ships to the surface with enough safety to make a successful landing and obtain a foothold to operate from you are going to have to knock out anything that shoots into LEO at a minimum over a large region. Now once that is done with it gets a bit harder to do anything without massing forces to contest a landing.
The best way is focus around a few select locations so you can leverage fire power in order to land where you want. Remember not all of the planet is a suitable LZ so no you can't land anywhere anytime.
It isn't impossible but it isn't going to be easy either and it is going to take a pretty large sized force with the support train that entails to pull it off.
Fox: Actually 12 digit bodies is not overkill it is very much what will likely be needed to do the job.
Have fun seizing and entire planets worth of infrastructure. It is not that easy either.
edited 23rd Jan '15 6:49:32 PM by TuefelHundenIV
Who watches the watchmen?To simplify the analogy, it's like an amphibious landing on an island stronghold. If your landing craft never reach the beach you'll never defeat the stronghold. Same principle with orbitals.
Because glassing the surface is not an option. It is also not a guarantee at all especially with large military bodies that will you be able to take out all of the military from orbit alone. That is just as flawed thinking as saying you can win with airpower alone. From interception systems meant to give cover against such assaults to bunkers and shelters and just not being where the bombs are obviously going to fall it is almost certain there will be more then a few left to make any landing force miserable. Plus you are going to take casualties lots of them. You are going to need near 12 digit bodies of troops to take and hold a planet effectively.
If you tried to bomb every possible threat overall from orbit you are going to run out of things to shoot at the enemy before you run out of potential targets. If anything focusing on a more local region gives you a reasonable shot at creating a beach head you can hold and cover without expending every round in your magazines and land forces at. Your forces then sweep out and clear defenses that protect against that air cover. Every time they snuff out a defense groundside that is fewer munitions you have to expend to hit a single target.
Your initial expenditures are going to be high to create the breach but done smartly and with proper combined arms action your expenditures are going to be dropped off and more smartly used against targets that require fewer shots to hit.
Who watches the watchmen?Not really. There's not even 12 digits worth of people on this planet today and we as a species control pretty much the entire surface. Less than 10% of that number is military.
You don't need a million troops to pacify and occupy a city/county/state/province with a million people.
edited 24th Jan '15 6:43:55 AM by MajorTom
Worth noting, Anti-Air defenses wouldn't even need to have full coverage of the orbitals to make landing dangerous. I'm picturing ICB Ms with MIRV-ish air-to-air missiles as a terminal attack phase. If your launching fleet can't swat the missiles in time, you'll risk having a Macross Missile Massacre unleashed right in the midst of your landing craft, or coming in from above them as they decelerate for landing.
Of course, if the defenders know where you're trying to establish a beachhead, they may just try to glass that part of the world before your forces can close the gap with them. So you have to balance reducing the time where you have your proverbial dick on the chopping block, while still ensuring you don't try to land within one of the nastier layers of their defense zone.
Really, if you have to take the planet, and they have any kind of established infrastructure and defense, it's gonna be ugly. That said, planets are huge, and I could easily see many planets having relatively sparse and/or poorly defended populations if they're just colony worlds.
The Armored Trooper VOTOMS Gilgamesh attack on Balarant Monad on the surface was a planetary invasion because the Gilgamesh lost it to politics around a hundred years ago and they want it back. With talk of hidden technology within the planet's core from a subset of humanity long since gone.
In truth it was a grand experiment to see if 5 picked troopers were Abnormal Survivors with getting the planet back just a added bonus.
It was considered a waste of money and time in universe but the Gilgamesh wanted it back a lot and felt it would be a nice show of power for the end of the war so they went through with it.
It did not work because the planet was destroyed (as it turns out ancient tech doesn't like being fiddled with) and the man responsible was branded a War Criminal. I was just stating how the statistics of the fight, well the rough estimate. Funnily enough they did manage to capture the ancient tech core of the planet officially meaning for a short time it belonged to the Gilgamesh again.
Even homeworlds can be that way. There's a lot of places on Earth an alien invasion could land tomorrow and not meet much if any military resistance initially. Places like the Canadian north, Siberia, the Great Australian Sandbox, the Amazon Jungle, the oceans, etc.
If you're really dedicated to protecting a planet you can network the anti-orbital batteries together. This way you can lob missiles from behind the horizon at attacking ships.
However, the best defense would be turning an airless moon and turning it into a battlestation. Taking something like that on would be a nightmare.
And of course, the question is also what are the tech capabilities of the planet you're attacking. If they're capable of Casual Interplanetary Travel, lobbing missiles at you from millions of miles away before you even reach the orbitals should be an option on their table, even if the missiles are ground-based. Then again, if they have that capability, you're likely slogging through a layered multi-planetary defense the whole way in, making this a much uglier proposition.
Tom: Try again. As it is our planet has a constantly expanding population. There are huge amounts of unsettled space on the planet. We are also talking about society whose potential population is multiple planets worth of people. Yes you can still need a 12 digit number to take, seize, and hold an entire planet. Not all of them are going to be trigger pullers.
Contested dense urban areas take a lot of man power to take, hold, and control period. The bigger the city the more you need. Case and point battle of Stalingrad had Millions of troops fighting over the city. They started the fight over the city in the many hundreds of thousands. That was in WWII with WII equipment with reasonably comparable technological parity for just Stalingrad. The casualty numbers in total were in the millions. Try repeating that for an entire densely populated heavily developed planet you are in for a slog one way or another.
Afp: That is exactly what I have been getting on about. Even close parity can make this really damn ugly from start to finish.
The only easy option is to avoid the planet or nuke it from orbit and say fuck it all.
edited 24th Jan '15 9:02:40 AM by TuefelHundenIV
Who watches the watchmen?They had to go back for the enemy eventually and that is when those fights happened. They also couldn't bypass every enemy island and had more then a few nasty fights to deal with. We talked about assaulting things like extreme or very high density urban environments in the past. How effective seizing the infrastructure is greatly depends on how it is laid out.
It is possible for structures of enough size to have their own internal infrastructure stored up or the infrastructure itself could be so large and complex that it is impossible to completely cut off all access without extensive and time consuming efforts. It would take examination on a locational basis to determine how effective it would be. If the city has only one or two real sources of things like power and water yeah that is easier to choke off. But if they have say several smaller power and water stations that feed the city from inside you need to take all of those to fully cut off the access or spend the time doing enough damage to cut off the access to the source.
Assaulting places like massive slums with no clear or fragmented infrastructure could be a challenge in and of itself.
edited 24th Jan '15 11:32:55 AM by TuefelHundenIV
Who watches the watchmen?And unless every planet out there worth fighting over or every homeworld is a fucking Coruscant-style City Planet there's going to be empty space out there every time.
Likewise you won't be needing that many to secure large swathes of territory. Sure not all your 100 billion troops sent are going to be light infantry, but you don't need that many even on the POG side. As mentioned we've done pretty good taking all the territory on this planet and less than 10% of the population is military (and maybe 15% of that are combat personnel).
You're thinking it's gonna be a World War One slog with infantry doing everything. You can keep tabs on a lot of ground even in contested airspace for a lot less manpower than a squad sized patrol every kilometer across every kilometer of the planet.
Tom: Yeah no not even close there. Wrong on many counts and missing so much.
First we have room to keep on growing and likely will do so unless something really bad happens. Increasing technological advances that mean increased effectiveness and efficiency of resources pretty much guarantees that.
Two no you don't have to be Coruscant to have large, extensive, and dense urban zones. We are already seeing that all over the world including the US with the sprawl steadily creeping into those "empty" spaces which are no where quite as empty as you make them out to be.
Three no we don't have good coverage with our military on the planet and no we don't have control over all of it. We can not take and hold multiple continents with out extensive efforts and trying would produce a serious butchers bill to the point it is not sustainable for us to try without a lot more then what we have now.
A first rate highly modernized and advanced 2 million man military couldn't hold Afghanistan a backwater 3rd world shit hole. We are talking a whole planet with a lot more development and very likely their own reasonably potent military. Oh and that includes what are likely to be very dense and very large urban areas. Doesn't work out for your end there tom at all. Especially when I gave an example that pretty much gutted your point already.
Who watches the watchmen?

Everyone has planetary assault wrong.
Planets are huge. Defending every square inch of them is a ridiculous, insane idea; it would take more troops than the planet could natively support, hundreds of billions. Such an attempt at defense would only invite siege and starvation, aside from the massive logistical issues of moving food and other supplies for that many people interstellar distances.
A planetary assault will never be about defending orbit from the ground either; this is impossible. They can always sit up further than you can reach and drop rocks on your weapons. You can and may even want to attempt this, but it will be a method to buy time for a response, not function as an actual defense capable of repelling the enemy.
The attacker, in any sane scenario, can always be assured of a successful landing; and it is to the defender's advantage that they land, since it forces them close together where they are safer from orbital attack. There will always be some hinterland that is undefended where the attacker can set down and stage his forces without fear of immediate attack while he unloads. This is because, again, planets are huge.
Rather, the primary issue with planetary assault is how to best mix the fact the attacker can always land with how best to ensure the defender is not able to entrench, disperse and go guerrilla (again, planets are huge), and/or destroy whatever makes the planet militarily or politically useful while the attacker advances to contact. Similarly, a properly equipped attacker will always be able to set up their own staging base; but this demands moving a lot of stuff interstellar distances and it may be on balance the attacker would prefer to immediately seize a more civilized and more likely to be defended area rather than bring everything they need with them.
edited 23rd Jan '15 5:35:55 PM by Night
Nous restons ici.