Zyobot

Just a time-traveling robot stranded on Earth.
Per Isaac Arthur’s thoughts on the subject, a common tendency I’ve seen in more militant sci-fi is the presence of ground forces. Interstellar navies have obvious uses, but I find it harder to figure out how terrestrial armies would actually work, aside from cases where the factions fielding them want to carry out “asteroid-hopping”, boarding operations, or occupy planetoids whose resources and infrastructure are to be left mostly intact, as opposed to launching orbital bombardments that leave excessive collateral damage or something.

This is further complicated by how sci-fi armies tend to employ approaches we twenty-first century people wouldn’t find out of the ordinary (once they’ve been deployed to the surface from space, anyway). In fact, some commentary I’ve seen even remarks that their tactics and approaches are even quite primitive, such as Warhammer 40K’s Imperial Guard relying on sheer numbers and stubbornness to drown the enemy out or the Droid Army on Naboo marching in large, easy-to-target formations that the Gungans can see coming from a million miles away.

I’m no expert on hard sci-fi or military history, but I’d think that all the technological breakthroughs and centuries of war-fighting experience that interstellar societies ought to have under their belt should drive considerable advancements in tactics and strategy. Naturally, this should extend to how terrestrial armies are used and what kinds of crazy hardware they employ, such as drone swarms or human soldiers walking around in power armor. So, what realistic uses would interstellar factions have for large terrestrial armies, and how would they likely be equipped and deployed to perform tasks that their naval or airborne counterparts are ill-suited towards? Note also that said ground forces don’t necessarily have to be comprised of organic soldiers; they can easily be more realistic versions of the Separatist Droid Army from Star Wars and still fit the bill, for example. Or, perhaps, a force that mixes and matches organic and mechanical troops, though how exactly they’d do this is also up for discussion here.

Here are some of Isaac Arthur's actual videos on the subject, for those interested. Hopefully, they provide a good basis for what I hope is to be a productive and long-running thread.

Interplanetary Warfare


Planetary Invasions & Assaults


The Next Century of War



Thank you in advance,
Zyobot
 

Zyobot

Just a time-traveling robot stranded on Earth.
If you want to take and hold ground, you need boots on the ground.

Copious amounts of boots on the ground.

I know less about how necessary boots on the ground would be for initial planetary invasions, though sending them in for boarding operations makes much clearer sense to me.

However, I can certainly understand why they’d be key for actually occupying territory, since you’d need (somewhat) independent thought-capable troops with the actual physical and mental dexterity to deal with whatever population they’re putting in line. They’d still be armed and trained/designed to defend themselves, of course, even if they engage in far less fighting than the drone swarms that preceded them. Ditto with expeditionary settlement after the first few probes come back with data and, perhaps, once the initial wave(s) of infrastructure has been set up by a construction bots sent to the Asteroid Belt or wherever.
 

bintananth

behind a desk
If you want to take and hold ground, you need boots on the ground.

Copious amounts of boots on the ground.
True. However, in a setting where space travel is easy enough that planetary invasions are on the table "he who controls the orbitals effectively controls the planet".

Ground troops would logically be more of an occupation force than an invasion. They're there to make sure the locals don't cause trouble and to deal with the ones who do.

(There are of course exceptions, like a xenophobic society that wants to exterminate every sentient life form except themselves.)

If the planet contains some sort of rare resource worth fighting over without wrecking the planet in the process, the resource should not be something laughably easy to obtain through other means at this tech level ... which rules out everything on the periodic table along with practically every chemical compound you've come across and catalogued.

It should be something like goats milk - to use a silly example - that's only on one planet. Suppose that turns out to be some sort of miracle cure for all sorts of alien ailments but goats, for whatever reason, can not be raised anywhere but Earth. If Earth decides to ban the export of goats milk a whole bunch of angry aliens are going to come-a-knocking and they aren't going to risk wrecking Earth when they do.
 
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PsihoKekec

Swashbuckling Accountant
Ground forces fighting it out might be due to multiple factors, infrastructure that you don't want destroyed, friendly population you don't want massacred via ortillery, fragile ecosystem... It was already touched upon as the reason for existence of mobile infantry in Starship Troopers, navy can well glass every world with enemy presence, but that is a rather poor approach if you want those worlds habitable for your own use.
Then there is also matter if the sides have something akin to Geneva or Ares convention in effect. Even with such convention the orbital supremacy is still a big advantage to the attackers, so the defenders are at most stalling for time, for friendly space relief force to arrive or doing a last stand.

There is an interesting case in the webcomic Crimson Dark, where it is normal for worlds to surrender once the orbitals are taken, but one world refuses to surrender, stalling the Republic advance as they blockaded and ortilleried the world in effort to crush the resistance.
 

Atarlost

Well-known member
Another possible answer is fortifications. Planets are great honking huge heat sinks. If you have big capital ship beam weapons that can fire down through atmosphere with useful precision they can also fire up through atmosphere and a planet can keep firing long after a starfleet has had to break off and deploy radiators. If armor is useful in your setting they can also have a degree of armor that would be preposterous for anything subject to the rocket equation. If they don't scale down smoothly they may be unsuitable for shooting drop pods or small shuttles. Or a fleet may be able to concentrate enough firepower to put one or a few fortresses out of action create an area where it can get troops through if they follow a steep enough reentry trajectory.

If the sources of asteroids are also settled a large asteroid isn't quite as deadly a fortress as a planet, but it still has a lot of thermal mass and isn't going anywhere so it can be more armored than any mobile spaceship and have more combat endurance. This can make it impossible to source large kinetic bolides locally. If FTL doesn't allow bringing bolides in from somewhere else you either have to infiltrate ground forces to take out the planetary fortresses directly or to take out the asteroid fortresses so you can tow asteroids into intercepting orbits. Or start your bolides in another system requiring much higher sublight velocities and taking years to line up a shot. This is problematic because while planets don't shift orbits significantly on that time scale political realities can change dramatically.
 

bintananth

behind a desk
@Atarlost

I wouldn't put too much faith in armour or fortifications protecting against precision beam weapons. An engine pulled off a Vespa can generate more power than a cutting laser rated for 5/8" of steel needs.

A linear accelerater used for cancer treatment is stuffed in a 3ft thick concrete vault with 6 feet of concrete and an inch of lead in the directions the beam can be aimed in and the opposite direction. The last time I looked at plans for one of those vaults was back during Obama's 1st term and we were renovating it.

Nuclear reactors need similar levels of radiation shielding.
 
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bintananth

behind a desk
BTW: Y'all should take a look at this video which shows 45 years of asteroid discovery:



The largest dots in the video:
- The Sun
- Jupiter
- Earth
- Venus
- Mars
- Mercury
- Ceres
- Vesta
- Pallas
- Hyigaea

The Moon* is not shown. It's about 2/9 the mass of Mercury and dwarfs Ceres. The latter accounts for about 1/3 of the Asteroid Belt's mass.

* The Moon is about 1.8 times as massive as the combined mass of all the known dwarf planets.
 

Arlos

Sad Monarchist
I never understood this thing about sci fi, where does this «if you hold space you auto-win » ideas come from? As far as I am concerned, unless you start going into moon sized ships, that’s just not the case, unless you don’t want the planets of course, ground to space should be much powerful than the opposite, if only because of the differences of energy at their disposals, a ship will always be limited in energetic output for it’s weaponry by it’s size, meanwhile, ground defense even without dedicated reactors could just redirect locals energy ressources in time of need to go straight trough any ships like it’s made of butter.
In term of energy, ships would be nuclear air carrier and the planet would be the entirety of the USA.
So unless you are willing to bullrush it with your ships and hope to take out the defenses before your fleet melt away, the best solutions would be ground assault to take out local planet to space defense or energy productions means.
 
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Atarlost

Well-known member
@Atarlost

I wouldn't put too much faith in armour or fortifications protecting against precision beam weapons. An engine pulled off a Vespa can generate more power than a cutting laser rated 5/8" of steel needs.

A linear accelerater used for cancer treatment is stuffed in a 3ft thick concrete vault with 6 feet of concrete and an inch of lead in the directions the beam can be aimed in and the opposite direction. The last time I looked at plans for one of those vaults was back during Obama's 1st term and we were renovating it.

Nuclear reactors need similar levels of radiation shielding.
Such armor may be handwavium or unobtanium, but I think it's handwavium or unobtanium you have to have to write space battles on a larger scale than American and Russian spaceplanes disabling each others satellites. To have a space battle both sides must each be confident enough in their ability to defend themselves to not either fall into a MAD enforced peace or to go out and systematically eliminate all potential competitors before they can build up the infrastructure to be a threat. If there is no defense against orbital bombardment then everyone keeps SSBN analogues in interstellar space and any victorious space fleet will come home to ashes. And if space cruisers can survive loitering close enough to planets to conduct bombardment an SSBN analogue can just be a normal space cruiser whose crew is pissed off enough to kamikaze the planet of the people who just depopulated the planet all their families lived on. Everyone has to believe their important planets can withstand a siege long enough to be relieved as a precondition to getting involved in open warfare with an off-world adversary that has the capacity to fight back.

You're also completely missing the point about unlimited mass budgets. A space cruiser might have to settle for 5/8" thick armor. It has to pay for every gram of payload with even on a fairly handwavy but Newton compliant drive with multiple grams of propellant. An asteroid fortress would consider 5.8 meters a start and maybe not a very good one. A planetary fortress may bury the power plant and lasing medium 2-4 kilometers down with lots of widely spaced and concealed redundant turrets it can switch the beam between.
 

bintananth

behind a desk
I never understood this thing about sci fi, where does this «if you hold space you auto-win » ideas come from? As far as I am concerned, unless you start going into moon sized ships, that’s just not the case, unless you don’t want the planets of course, ground to space should be much powerful than the opposite, if only because of the differences of energy at their disposals, a ship will always be limited in energetic output for it’s weaponry by it’s size, meanwhile, ground defense even without dedicated reactors could just redirect locals energy ressources in time of need to go straight trough any ships like it’s made of butter.
In term of energy, ships would be nuclear air carrier and the planet would be the entirety of the planet.
So unless you are willing to bullrush it with your ships and hope to take out the defenses before your fleet melt away, the best solutions would be ground assault to take out local planet to space defense or energy productions means.
A spaceship is tiny when compared to a planet and they're vastly more maneuverable than a planet side installation.

Consider the mass differences:

Space Shuttle: 74 tons dry and small enough for three to be displayed on an NFL football field with room to spare.
Earth: 6.585 billion trillion short tons.

Something the size of the Space Shuttle can avoid getting hit by practically everything unguided headed its way at starship battle ranges. Something on a planet the size of Earth can not.
 

The Whispering Monk

Well-known member
Osaul
The other point to bring up is that a Space-going Warship may not need to even be in close orbit or 'in the neighborhood' to be a threat to a planetary body.

Harrington-verse is a prime example of this type of weaponry. Take missile that weighs anywhere from 20-100 tons. Accelerate said missile at around 1,000 gravities, and aim it at a planet. The sheer kinetic energy of a C-fractional stike is...well, frankly inconceivable. It easily passes Gigaton range yields. A few of those and the planet is just toast, at least for life on the surface.

At that level of effect, the only thing holding people back is the accepted rules of war.

So, really, if you care about sentient life, you need a ground force. If you don't, be prepared to slaughter your way through Billions (maybe Trillions) of sentient beings...and then have it done to your worlds.

---------

So...in order to get your soldiers dirtside you need a couple of things (well MANY things to be honest)

1: A method of securing a somewhat stable drop zone. This means you must be free to send the troops from your ships to the ground. Requires either domination of the orbitals or a suppression of the defensive fire in order to get the troops out.

2: Protection for the troops do they can get to kissing dirt. ECM and Stealth so that deffensive systems can't effectively target the troops and/or their dropships. Shields and armor to protect them if they do get hit. Speed to make sure their time of exposure is limited as much as possible.

3. Ability to do secure a beach head. Now is where it gets REALLY tricky. How much ground must your forces clear so that they can reasonably protect their supply and logistics. Can you beam them stuff not that they are groundside (gotta love those teleporters!) Do you need to constantly suppress anti-air assets in order to orbitally insert and launch aerospace assets to carry the beans and bullets your troops need?

4. Comms is a whole separate field here. Can you actually obtain secure communications inside the atmosphere while under what is likely extreme ECM conditions? If you can't, you're plan is FUBAR and your troops are likely toast.

5. Ability to supress air attack from the ground. You'll probably have some sort of Air vs Air component, but you'll need this to protect your beachhead and avenues of attack while your air assets are occupied or suppressed by ground fire.

6. Mobility is key. Can you reposition your assets where you need them WHEN you need them. Aircav or high speed armor/mech are necessary here. (How did you land those assets from orbit?)

7. Infantry in Armor. This tech level is stupid at killing. Man portable pistols and guns would likely shred modern tank armor. You need this and you need to be able to keep it working.

8. Command and Control. Commanders have to have a plan. REALLY need to know the enemy and their capabilities. That way you know what needs to die soonest. Then you need people at the line level to motivate and organize the forces and line leaders to get the grunts to do the work.

Specifics will vary depending on tech.

Harrington-verser actually has a pretty good understanding of the tech's ramifications on a field of battle.
 

The Whispering Monk

Well-known member
Osaul
A spaceship is tiny when compared to a planet and they're vastly more maneuverable than a planet side installation.

Consider the mass differences:

Space Shuttle: 74 tons dry and small enough for three to be displayed on an NFL football field with room to spare.
Earth: 6.585 billion trillion short tons.

Something the size of the Space Shuttle can avoid getting hit by practically everything unguided headed its way at starship battle ranges. Something on a planet the size of Earth can not.

At the level of tech we're talking about...the only thing 'unguided' are going to be light-speed weapons. Surface - Orbit there is not time to dodge.
 

bintananth

behind a desk
Such armor may be handwavium or unobtanium, but I think it's handwavium or unobtanium you have to have to write space battles on a larger scale than American and Russian spaceplanes disabling each others satellites. To have a space battle both sides must each be confident enough in their ability to defend themselves to not either fall into a MAD enforced peace or to go out and systematically eliminate all potential competitors before they can build up the infrastructure to be a threat. If there is no defense against orbital bombardment then everyone keeps SSBN analogues in interstellar space and any victorious space fleet will come home to ashes. And if space cruisers can survive loitering close enough to planets to conduct bombardment an SSBN analogue can just be a normal space cruiser whose crew is pissed off enough to kamikaze the planet of the people who just depopulated the planet all their families lived on. Everyone has to believe their important planets can withstand a siege long enough to be relieved as a precondition to getting involved in open warfare with an off-world adversary that has the capacity to fight back.

You're also completely missing the point about unlimited mass budgets. A space cruiser might have to settle for 5/8" thick armor. It has to pay for every gram of payload with even on a fairly handwavy but Newton compliant drive with multiple grams of propellant. An asteroid fortress would consider 5.8 meters a start and maybe not a very good one. A planetary fortress may bury the power plant and lasing medium 2-4 kilometers down with lots of widely spaced and concealed redundant turrets it can switch the beam between.
You should read the story I'm writing and sharing here. An ancient society older than the Sol System got dragged into a conflict with Earth due to ancient defence treaties actually does have to worry about human weapons and is trying to warn them that they're about to blow up the Sun if humanity doesn't discontinue a certain line of FTL research and is trying to protect them from some teenage anger.

Note: The the aliens won't be the cause of the supernova. The drive system is and the aliens accidently blew up a galaxy while using that type of FTL.
 
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Emperor Tippy

Merchant of Death
Super Moderator
Staff Member
Founder
As with many things in Sci-Fi, it partially depends on the technology present.

Very few settings have ships that operate on the scale of planets, which means that if you can do shielding of various types then you will always be able to put more power generation and larger shield generators on a planet than on a ship (or even fleet of ships). Planetary shields with some allowance for relatively low velocity penetration while blocking proper orbital strikes mean that taking a planet requires ground forces.

If you do your shielding remotely intelligently, you probably also include some component to disrupt detailed orbital surveillance. When your shield is distorting your surveillance platforms, guided/precision strikes get even more difficult.

Or take 40k, their orbital to surface weapons and surveillance capabilities are generally abysmally bad. Yes, they can pot shot a city but that is basically their definition of a precision strike. If the IoM wants infrastructure remotely intact then that means ground forces.

Stargate is in many respects the opposite extreme. The Jaffa are a slave policing force, nothing more. When the Goa'uld do proper "war" they park Ha'Taks in orbit and use variable yield plasma weapons that can do everything from precision strikes on par with a frag grenade all the way up to 200 megaton blasts rapid fired. Or when the Asgard decide to conquer a planet, they just use Go Away beams to remove every hostile on the planet in a matter of minutes. Useful ground forces in that universe are basically a precision strike asset doing special forces missions.

Or you have the Honorverse approach, where ground forces basically exist purely for the same type of precision strikes and as occupation forces because once a warship is in orbit they can utterly negate any kind of large, hostile, ground force.
 

bintananth

behind a desk
At the level of tech we're talking about...the only thing 'unguided' are going to be light-speed weapons. Surface - Orbit there is not time to dodge.
Sorta.

If you're about 80% of the way to the Moon from the Earth's surface it'll take a light-speed "ping" about a second to get to you and another second for the return signal to reach where it was sent from and be processed.

You've got ample time to dodge at those distances.
 

The Whispering Monk

Well-known member
Osaul
Sorta.

If you're about 80% of the way to the Moon from the Earth's surface it'll take a light-speed "ping" about a second to get to you and another second for the return signal to reach where it was sent from and be processed.

You've got ample time to dodge at those distances.
Assuming your sensors are FTL capable. Otherwise, you realize you're being shot at when you're hit.
 

bintananth

behind a desk
Assuming your sensors are FTL capable. Otherwise, you realize you're being shot at when you're hit.
Fire control.

If you can't estimate where your target will be when the shots get there you might as well be firing blind. A WWII-era battleship's electro-mechanical fire control systems, if designed for time to target at light-speed and starship combat, could probably bracket a target a third of the way to Mars while orbiting Earth.

BTW: That was light-speed, not FTL.
 

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