Planetary Invasions

In science fiction the idea of our planet being invaded, or other planets being invaded, is sufficiently old enough to be a trope. It all started back when H. G. Welles imagined Martians slinging themselves towards Earth to mash us with their tripods and death gas. From there it's evolved into many different scenarios some of which still involve us on Earth, to fascinating wars between the stars of other human or alien civilizations. Recently I've been pondering on that after I watched two very interesting videos between people who examined the idea of planetary invasions.

The first is from the excellent channel Space Dock which puts together wonderful work on the spaceships and vehicles of many franchises. They themselves have a drama called the Sojourn coming soon. Definitely check it out. But for our purposes watch their brief video on Planetary Invasions.

In contrast we have one video from Isaac Arthur discussing the subject. It's a longer one and it raises many interesting points. His channel is simply amazing for an in depth look at futuristic science based concepts on how we may do things in the future. It's honestly one of the best futurist channels and series I've ever encountered, sincerely worth checking out if you're interested in that kind of thing.

Credit to Alexander Tooth, from wookiepedia

Both these videos raise very good points, and they have contrasting opinions. In the first video we do see that it is argued that a planetary invasion is basically infeasible. Some Operation Barbarossa style mass landing and invasion taking years, decades, or perhaps centuries, to fully pacify a planet through mechanized warfare from above and below. The crux of the argument is that this is a huge waste of time and resources, especially when you presumably have ships in orbit that can hammer your opponent at your leisure. Then if you have no hope of relief and no friendly ships in the area, fighting on serves no purpose. You don't need legions of soldiers, just large landing forces to take and hold the vital aspects of planetary infrastructure and then garrison forces to keep the planet yours.

The second video has a more wide ranging view. It presumes that planetary assaults or invasions are feasible. The main point is that, after all, if you're jetsetting around in space with any sort of casual interstellar travel then the mobilization of resources to invade and crush another world or system of habitats (especially if you rule over multiple star systems and have great automation) is almost trivial. That being said, it makes a very pertinent point that a planet is not necessarily a helpless target. 

It is a point worth considering as any civilization which can do travel casually at interstellar distances is probably not really having to worry about the whole issue of delta-v in a gravity well. That means that, while an opponent who does control the orbitals has an advantage, the people at the bottom of that well are not nearly so defenceless as we might assume through our lens of 21st century technology where an asteroid barreling through our gravity well is a very terrifying prospect. Your vital sites are probably ringed with powerful railguns or missile batteries which can shoot destruction at any ship foolish enough to park in orbit.

From the BBC

In fact with that view, the traditional image of a ship parking itself in orbit and blasting a planet with it's weapons seems silly. No ship could risk parking in orbit without worrying about taking crippling damage or being rendered combat ineffective. The proper image might be a vessel in the age of sail bombarding a land fortification and having to outnumber the guns of the fort to hope to overpower them before it can be rendered ineffective itself. The planet can shoot back.

What you might see instead is ships engaging in what amount to bombing runs, first moving to cripple or take any orbital defences, then moving in unpredictable patterns to try and crush the ground based defences. If that doesn't work, clearing a landing corridor to insert marines who can disable or capture those defenses so the fleet can put itself in a position to command the ultimate high ground and compel a plant's surrender would be your next best bet. In the book Tiamat's Wrath there is an interesting example of this that works very well from both a tactical and a dramatic perspective.

This is actually a point I've considered for some time. I've mused about interstellar warfare before and why it might happen. In my own, as yet unfinished Service to the State science fiction novel, I've thought about how you could make a planetary invasions feasible, so my own view actually falls somewhere between that of the two videos.

Part of that view does come from finding that in universes like those of the Honor Harrington series that if you've countered gravity to the point you're using it in your weapons, the idea you can't make some kind of planetary based weapons system which could cripple or severely damage a ship seems baffling. It does seem to me that there would need to be an invasion, but one aimed at very limited and achievable goals so your fleet could enforce the threat of death from above.

Some blame might come from Robert Heinlein's Starship Troopers which, though an excellent novel I recommend everyone read, did draw it's inspiration pretty heavily from the work of paratroopers in WWII and the island hopping campaign in the Pacific theater. In the Pacific the small Japanese garrisons which held out across numerous little islands with their coastal batteries and then fighting to the last man against the power of the American gun line and the overwhelming firepower of Marine divisions set the course for the campaign. The Japanese might have inflicted casualties, but they had only the small resources of their islands to call upon and no hope of resupply. This has, I think, colored interpretation of how planetary assaults might go. A planet doesn't generally have that problem unless you wreck the infrastructure so thoroughly that further resistance is simply futile.

In Isaac's video he makes a very good point about the resources of a planet, and how future technology might make it possible to basically weaponize an entire planet's population, or make them know no fear. However, even with fantastic automation or fearless soldiers, there is a point where your offensive options and economic support would be so ground down that your ability to resist is functionally irrelevant as the invading power could zap you whenever they felt like it and destroy or immobilize your remaining assets. At that point, it's either guerrilla resistance or surrender.

That's why in my mind I think a planetary invasion might fall somewhere between these extremes of Honor Harrington and Starship Troopers. A planet isn't defenceless unless it has no real orbital defences or ground based weapons, and even with those ships can work to attire them, and then send in the marines to seize and hold them until the fleet in orbit can establish an advantageous position. Unless you know you have a relief fleet coming, there's no reason to keep fighting.

Of course, this is all just speculation and trying to harmonize the plausible with the realistic and make compelling story telling. Future warfare is liable to be so destructive it's unimaginable to today's soldiers or civilians. It does make for interesting reading or musings though.