Interplanetary Warfare

[Caiaphas]

Situation is like this: there's two planets, around Earth-Mars distance. Both have around the same tech level, which is to say semi-casual interplanetary travel (for the military, at least), research beginning into an antimatter industry, coilguns powerful enough to send a one hundred kilo payload into orbit from a kilometer-long launch rail, but an incapability of directing asteroids larger than 50 meters across without significant applications of time and money.

They're at war. Question is, how is war waged? Highly effective antimissile laser systems are already in place on both planets, the asteroids that are small enough to be moved around have all already been mined into dust, and most of the larger asteroids suitable for planetary bombardment are being mined currently.

I was thinking of some sort of orbit-based coilguns around each planet, gigantic structures that are almost like artificial planetary rings, for use in long-range bombardment. Only problem is, how do you counter these massive projectiles heading towards you at dozens of kilometers a second?

Any help will be greatly appreciated.

[Zor]

You large numbers of long range missiles which are basically large engines with large slabs of metal on the front end in place serving basically the same roll that ICBMs do in modern warfare with a few ships armed with lasers and missiles designed to hopefully be able to intercept the enemy missiles before they hit each others planet and maybe intercept each others interceptor spacecraft so that secondary volleys can get through.

Zor

[Sea Skimmer]

Yeah just placing any object in the path of a 24km/s+ object is going to lead to that object shattering into millions of pieces. Even if a asteroid 50 meters wide was to to get as far as to begin to enter a planets atmosphere you could still shatter it with a hit to kill missile, and then immediately vaporize the pieces with a nuclear warhead at worst. Or really, just shooting enough ABM type hit to kill interceptor missiles could break up all the pieces until they are too small to survive reentry. Lasers would also help, but they have pretty limited effectiveness against a high speed object in the atmosphere because it develops a coating of plasma that will scatter the beam. Space based lasers would work much more effectively of course.

All and all though, it seems unlikely that a long range planet to planet bombardment using dumb slugs of metal fired from coilguns, or random small asteroid bombardment would ever be effective. The enemy will have too much warning time, and too many options to deflect or destroy the incoming objects. Such bombardment is useful for harassment though. A coilgun going all the way around a planet is not realistic, I'm pretty sure no material would be strong enough to make such a structure work and the cost would be insane even if it could.

All and all nuclear weapons make a lot of sense as they always do, because they can pack a lot of firepower into a very small package. You could attack using nukes a lot of ways. One would be a shear swarm of warheads, another would be to create very high end delivery systems that try to fight through. Think about something like missile that's more complicated then a fighter and has all kinds of active defenses a long with a lot of armor and many warheads on board it releases as it reenters an atmosphere. Enemy lasers could be countered with your own lasers burning up the enemy laser optics. So dedicated laser escorts might come a long for the ride.

Stealth would be another option. A very advanced stealthy warhead system might be invisible to radar, reflect almost no light making it near impossible to spot on radar and employ some kind of internal heat sink which keeps its skin cold for the duration of the flight. Even if 99% of the stealth warheads failed just a few slipping through could cause a lot of damage.

It would of course help to establish an advanced base near the enemy planet, close enough to allow for the use of much smaller weapons that aren't effective over true interplanetary distance. Since each planet would be fortresses like a lot of fighting would center around establishing and destroyer these bases, which have no need to be tied to any specific moon or asteroid or other 'physical object'. They will work just fine in deep space. A physical object to build the base on would only be helpful if it had a resource like water or ice you could use to make energy.

[Fingolfin_Noldor]

What do you mean by causal interplanetary travel? Are they highly dependent on sling shots etc.?

[GrandMasterTerwynn]

Situation is like this: there's two planets, around Earth-Mars distance. Both have around the same tech level, which is to say semi-casual interplanetary travel (for the military, at least),

I'm going to assume you mean "semi-casual" as "semi-causal" makes almost no sense whatsoever.

They're at war. Question is, how is war waged? Highly effective antimissile laser systems are already in place on both planets, the asteroids that are small enough to be moved around have all already been mined into dust, and most of the larger asteroids suitable for planetary bombardment are being mined currently.

Very carefully. It already sounds like they're in a Mexican standoff. Any attack capable of breaching either planet's defenses would result in an extinction-level event due to the overkill required. So either they will settle for shooting holes in each others' spaceships, getting hundreds or thousands of spacers pointlessly killed, and negotiating a peace involving payment for the winner's ships . . . or they'll launch a massive assault and hope it'll kill the opposing planet worse than the opposing planet's response will kill them (since either side would have lots of warning of an incoming attack.)

I was thinking of some sort of orbit-based coilguns around each planet, gigantic structures that are almost like artificial planetary rings, for use in long-range bombardment. Only problem is, how do you counter these massive projectiles heading towards you at dozens of kilometers a second?

With the same laser beams that you'd use to shoot down missiles. All you need to do to deflect a passive projectile going at dozens of kilometers per second is induce a velocity change on the order of a few meters per second. You could use lasers to do that. Or use coilguns to shoot smaller projectiles at the incoming projectiles. The goal would be to deflect, not disrupt. Disrupting would turn the one projectile into a space-going shotgun blast.

[Caiaphas]

I don't have long right now, so I'm answering only the simplest point right now. More will come in later days. Sorry.

What do you mean by causal interplanetary travel? Are they highly dependent on sling shots etc.?

I suppose that I mean that a fueled-up, armed military ship can head from Earth to Mars in a straight line, in two months flat or less if they really have a short schedule. And this is a ship weighing in at nearly a million (metric) tons.

[mdiinican]

I don't have long right now, so I'm answering only the simplest point right now. More will come in later days. Sorry.

What do you mean by causal interplanetary travel? Are they highly dependent on sling shots etc.?

I suppose that I mean that a fueled-up, armed military ship can head from Earth to Mars in a straight line, in two months flat or less if they really have a short schedule. And this is a ship weighing in at nearly a million (metric) tons.

It doesn't seem like you could have a war that would achieve much unless you're prepared for genocide. Logistically, either side will need a huge advantage over the other if they plan on landing and supplying troops on the other's planet. And any anti-missile defense can be breached by sufficient numbers of sufficiently difficult to kill missiles. A planet is quite a lot of area to defend, and chances are not everything is going to be on the equator, so there will need to be satellites on polar orbits and such to defend cities.

The attacker could build maneuvering, armored missiles and, using their observations of satellite orbits, predict when the fewest satellites will be over a particular city and send enough missiles that the orbiting lasers will either not be able to kill them all, or that they overheat trying, allowing even more to get through.

Well, if they felt like it, they could use the engines for a ship like that and use it to propel an empty ship-like object massing about a milliion tons as a projectile. Give it some maneuverability and a number of layers of whipple shields as armor against mass drivers. Depending on the range of the lasers and mass drivers, it should get close enough to the planet to guarantee it will hit fairly close to it's intended target before it starts getting shot up pretty bad. If it's sturdy enough, a good chunk of it should make planetfall and mess stuff up.

[Rossum]

Question: Would it be practical or even possible to use a system of solar arrays to throw an enemies planetary environment out of whack?

For example, building a massive solar array and then parking it in an orbit so that it prevents the suns light from reaching the planets surface.

Or building more arrays that gather solar energy and then fire a constant beam of energy towards the planet in order to increase its global temperature. Set up a sufficiently huge number of these and set the planet up for artificially induced global warming.

Though, if you're going to setting up the massive number of arrays needed for such endeavors, they would naturally be equipped to send that energy in usable form to the planet that produced them.



Actually, if there are two planets in the same solar system, then one of them would likely have to be closer to the sun and therefor have more access to renewable solar energy, while the other would probably be closer to the asteroid belt (if that solar system has one... or if its in that location) so it would have better access to asteroids and the minerals inside them. So they would have somewhat different resources to work with.

[Caiaphas]

Well, if they felt like it, they could use the engines for a ship like that and use it to propel an empty ship-like object massing about a milliion tons as a projectile.

Wouldn't that only carry a KE of somewhere around 2 kilotons, assuming it's slowed to somewhere in the vicinity of 3 km/sec by the atmosphere, and that it carries most of its original mass on impact? You'd need to sacrifice a lot of ships if you were going to do any significant damage, wouldn't you?

Or building more arrays that gather solar energy and then fire a constant beam of energy towards the planet in order to increase its global temperature. Set up a sufficiently huge number of these and set the planet up for artificially induced global warming.

Except that they'd make nice large, huge targets for weapons systems. You'd need to eliminate enemy weapons first, and by then they're useless. Great as a terror weapon, though. You ever seen Die Another Day?

Actually, if there are two planets in the same solar system, then one of them would likely have to be closer to the sun and therefor have more access to renewable solar energy, while the other would probably be closer to the asteroid belt (if that solar system has one... or if its in that location) so it would have better access to asteroids and the minerals inside them. So they would have somewhat different resources to work with.

Hadn't thought of that... thanks.

With the same laser beams that you'd use to shoot down missiles. All you need to do to deflect a passive projectile going at dozens of kilometers per second is induce a velocity change on the order of a few meters per second. You could use lasers to do that. Or use coilguns to shoot smaller projectiles at the incoming projectiles. The goal would be to deflect, not disrupt. Disrupting would turn the one projectile into a space-going shotgun blast.

So you would use the lasers to vaporise parts of the incoming projectiles to produce a small thrust? And wouldn't that shotgun blast just burn up harmlessly in the atmosphere if the projectiles are sufficiently small?

A coilgun going all the way around a planet is not realistic, I'm pretty sure no material would be strong enough to make such a structure work and the cost would be insane even if it could.

Yeah, you're right. Scrap that idea. But how are you going to get a large projectile going fast enough to do some serious damage to a planet elsewise?

Thanks for responding, everyone. You've given me a lot to think about, and I'll try to get up a warfare scheme up on this thread within a couple weeks.

[lPeregrine]

So you would use the lasers to vaporise parts of the incoming projectiles to produce a small thrust? And wouldn't that shotgun blast just burn up harmlessly in the atmosphere if the projectiles are sufficiently small?

No. The energy still has to go somewhere, breaking up an incoming asteroid just means it gets dumped into your atmosphere in the form of lots of little stuff instead of one giant rock. If you're talking about something that started with civilization-ending energy levels, you're still just as dead.

Yeah, you're right. Scrap that idea. But how are you going to get a large projectile going fast enough to do some serious damage to a planet elsewise?

1) Gravity. Put it into an unstable orbit and let the target planet's gravity do the rest.

2) Long distances. You don't need huge acceleration if you can do it over long periods of time. For example, a mass driver using parts of the asteroid itself operating over months of time to bring it onto a proper collision course.





Also, you may wish to think about non-traditional methods of war/conflict. You've set up a universe in which pretty much the only way to force an end to a war is either by complete extermination of the other side (see previous posts on the impossibility of a successful invasion and occupation), or a credible threat to do so. Otherwise, you're going to be limited to minor skirmishes/acts of terrorism/etc. Kind of like the war in Iraq, there will be shooting and effects felt each side, but the average citizen will be sitting at home watching the latest war news on TV.

Or let's take this one step farther: let's say one side gets enough of an advantage that they can force an end to the war. And since there is no stealth in space, the other side is going to be aware of just how doomed they are. So why actually fight a battle? It is in the best interest of the superior force to offer surrender terms so there is more than just a radioactive wasteland left to conquer, and it is clearly in the best interest of the inferior force to accept those terms and avoid complete destruction. Instead, why not invite representatives of the other planet to your shiny new doomsday asteroid and explain the concessions they are going to be making in the near future? Or perhaps there is a third party, and both sides are playing political games to try to win an alliance which will shift the balance of power decisively in their favor? The "war" might end in a senate vote without a single shot ever being fired.


Or, let's assume you really want to have some shooting. You could write the story from the point of view of a warship crew staging a false-flag attack on the neutral party's asteroid industry in an effort to provoke outrage against your enemy and win that war-ending alliance. Or from the perspective of terrorists freedom fighters sneaking onto the rival planet to blow up a critical target and convince the government that it would really be cheaper to just pay that extra 10% import tax instead of suffering more attacks. The possibilities are endless.

[Caiaphas]

No. The energy still has to go somewhere, breaking up an incoming asteroid just means it gets dumped into your atmosphere in the form of lots of little stuff instead of one giant rock. If you're talking about something that started with civilization-ending energy levels, you're still just as dead.

Whoops. Forgot about that.

[Axiomatic]

The first question to be answered is, why is the war being waged? What is the purpose of the war? What do those participating in the war expect to get out of it?

This will obviously impact the method by which the war is waged. If my planet is overpopulated and I want to settle on your planet, then turning your planet into an uninhabitable ball of slag is...not smart. If I'm upset that certain trade treaties between us favor you and not me, then again, wiping out your civilization doesn't really help me, since my aim was to still keep trading with you, but at a rate that favors me more than you.

If I feel threatened by your existence and think my planet is more likely to endure in a universe entirely lacking in the "you" element, however, it would be in my interest to pursue a war of extinction.

[PeZook]

No. The energy still has to go somewhere, breaking up an incoming asteroid just means it gets dumped into your atmosphere in the form of lots of little stuff instead of one giant rock. If you're talking about something that started with civilization-ending energy levels, you're still just as dead.

Whoops. Forgot about that.

Funnt thought: such heating would be beneficial for Mars, not so much for Earth.

[Commander Xillian]

Dunno if it's been said before, but what ever.

I personally am of the thought process to just launching high-powered ICBM's at one another willy-nilly until one get's passed Anti-missile counter-measures and hits. Rinse and repeat as often as needed until one team gives up and they both go to the negotiations table. So, not only are space-to-space craft battles not needed and would be a waste of human life, but using the planets themselves like a 16th century ship-of-the-line would be more efficient, in terms of time spent. Never leave your home, and get more favorable results!

[Sea Skimmer]

Dunno if it's been said before, but what ever.

I personally am of the thought process to just launching high-powered ICBM's at one another willy-nilly until one get's passed Anti-missile counter-measures and hits. Rinse and repeat as often as needed until one team gives up and they both go to the negotiations table. So, not only are space-to-space craft battles not needed and would be a waste of human life, but using the planets themselves like a 16th century ship-of-the-line would be more efficient, in terms of time spent. Never leave your home, and get more favorable results!

You don't seem to have much concept of how expensive that would be, and how easily it would be defeated. ICBMs are extremely inefficient weapons that only work well in the total absence of defenses. Scaling one up to have interplanetary reach would basically mean spending a half billion dollars per shot to deliver a few tons of warhead that takes several months to arrive. Since the enemy would have such long warning time, and you plan on ceding control of space to the enemy, they don't even need to use a big high performance interceptor missile to shoot it down (even then such a missile would only be 30-50 million). They can just send up a very small reusable interceptor drone ship that shoots the equivalent of a Stinger at the incoming missile and then returns to a space base to refuel. Or just puts a little rock in its path for that matter.

[Caiaphas]

Funnt thought: such heating would be beneficial for Mars, not so much for Earth.

Does anyone think that an effective strategy would be to blast those arrays into so much space dust, thus leaving the planet farther out slowly freezing to death?

[Rossum]

Actually, the physical features of the planet in question could change what the best tactics would be:

A planet with a thick or earth-like atmosphere would be able to burn up asteroids better than one with a thinner atmosphere. Maybe smaller kinetic fragments would be able to penetrate the atmosphere of a mars-like planet easier.

A planet with a functioning ecosystem would be more subject to damage by weapons that kill organic material (like bioweapons designed to destroy the ecosystem or climate altering weapons).

A planet with an ozone layer that protects against cosmic radiation would be better protected against radiation weapons. Lasers or energy weapons that would never make it past Earths atmosphere might make it through a thinner atmosphere.

Planets with lower gravity might be easier to dig in. With dirt weighing less, then it could be easier for inhabitants of one planet to dig huge bunkers or cities far underground where they would be protected from many types of bombardment. If the surface of their planet is naturally uninhabitable (due to unbreathable atmosphere, cosmic rays due to inadequate radiation shielding, or whatnot) then the inhabitants might build their cities underground as a matter of course (though it would also depend on the geological stability of the planet as well).

Planets with more technological infrastructure might be vulnerable to cyberattacks or EMP weapons. Not really sure how you could go about doing either in ways that would be much different than just dropping bombs or such.



What methods are people using to get their ships or weapons into space? If they are using space elevators or those coil-gun launcher things then taking those out would be a priority.

If the main defense against missiles or kinetic weapons is point-defense by lasers, could you make the metal slugs stealthy? Maybe shape them so that radar is deflected away and they can't get a decent lock on them and paint them jet black? Heck, maybe invent some sort of super fiber optic fabric that makes them invisible to the wavelengths people use to spot objects in space. Once you get the tech to make something invisible then it shouldn't be nearly as expensive to make something invisible as it is to get it into space in the first place. So, make all your missiles stealth missiles or something in order to give them a better chance at making it past the enemy defenses.

Or alternatively, make the missiles super polished and reflective to protect them against the defense lasers. Perhaps multiple layers are at work. When first launched the missile has a shell to protect it from that atmosphere as it launches. As it heads toward the enemy, it jettisons its shell to go into stealth mode to be extra hard to spot on long-range sensors, then as it gets close enough that its difficult to hide from the defenses then it jettisons that to sport an armor designed to protect against laser defenses while thrusters are used so it can take evasive maneuvers against the other attacks. Maybe it won't be that complicated, but with the long distances involved with missiles makes it necessary to give them at least some way to actively protect themselves from the defense systems.

[Ariphaos]

Whoever controls the sun's output wins. A few million established solar statites can deny attempts to disrupt them or otherwise replace them, and force a surrender by performing careful planetary burns. Rocks are slow and it would be difficult to get more than ~30 km/second out out a space-elevator launched firing platform.

If no one has such a network yet and/or it is small enough to disrupt from afar, the next goal would be to target the opposing planet's elevators by flinging stuff from their own. Whoever wins that conflict would then try to shift towards space denial (targeting enemy satellites, establishing their own over the opposing planet) while establishing aforementioned statite network (a process that will easily take decades).

[Imperial528]

This may be a bit late, but an idea occured to me. If these civilizations are able to wage war on the interplanetary scale (albeit obviously not as fast or efficiently as the singe planetary scale). I imagine one of them could construct a large, powerful laser on their planet or its moon so that it will line up with the target planet at least once a year, and once it is complete all they need do is hold out until they can fire, at which point, the target can kiss its ass good bye. The great part about it is that it takes place on a strictly planetary scale, and even if you mount it on a moon it isn't too far away to be difficult to defend.

[Imperial528]

Hence why I suggested building it on an orbiting moon if necessary, since heating up the target atmosphere is actually quite desirable. Since giving the enemy population a heat-stroke related death leaves much infrastructure intact.

And the size of the laser I am talking about probably couldn't be built well at all as its own orbiting station, due to the lens size and of course the power generators and cooling systems needed for proper, and if required, repeated firing.

[Imperial528]

True enough. And I know that the laser strength will degrade considerably (it will with the distance anyway, spreading in atmosphere out isn't much of a concern, since continuous firing would essentially boil the planet should that happen, which also means you don't need to fire at multiple points), which is why I am talking about a BIG LASER, the kind of laser that the orks would look at and say "almost enough dakka". Not to mention that, aside from infrared emissions, the target is a closed system, so the low energy per unit of area isn't so much of a concern if you can keep the energy per unit of time higher than the target can emit energy into space. And once it gets into the visible spectrum emissions, your job's been done for awhile.

Given that, it may simply be easier to build it on its own asteroid platform, or spacecraft.

Also, this plan assumes that what ever solid objects you lob at them (missiles, bombs, slugs, space craft) are shot down before they can be effective. It's a last resort plan really. Although, in some situations, this might actually be cheaper than continuously lobbing things at the other planet to no avail.

The size issue is exactly why it must be built in its own orbit, far away from the gravity of planets to disrupt its alignment.

Almost missed this, but if built on a moon or airless planet, the gravity disruption can be dealt with by simply adjusting for the change in the shape and length of the firing window, heck, the slight shift could be calculated by simple geometry. The gravity of a planet doesn't affect a laser all that much, if I was talking about a mass driver we'd have some issues, but I'm not. Same issues MD has also goes for rockets. Essentially, for my original idea the alignment of the laser would also be the alignment of the face of the moon it is on, so aiming is a matter of waiting until the calculated alignment window starts, turning it on, and then off when the window ends. Repeat if necessary. And depending on the planets' orbits relative to each other, you might have some pretty damn big firing windows, like, 24/7 firing over two months.

PS: I will happily do some math if the OP can mention the general alignments of the planets relative to each other, orbit lengths and all that, and any moons and their orbit lengths. But not now, since it's a bit late for me.

[Korgeta]

Picking the scenario of interplanetry warfare between earth and mars, both same tech.

Though, if earth maintained the same eco system and was maxed populated, whereas with Mars it has a number of domed colonies holding a populas that can support a war.

Use of resources: if the conflict took place 300yrs from now would mars despite it's smaller size have the advantage of having more resources and material needed for construction, would earth's overpopulation be a major burden during the duration of the conflict? Would Mars in have a more structured planetry defence, due to it's size, and has two moons orbiting it compared to earth's one? Would a domed populas be better protected from chemical or radiation fallout from space by the weapons used from or fired into the atmospehre?

I can see Missiles being even more effective guided weapons, that can detect and evade incomming firepower from orbital defence or weapon platforms from the surface. Other then that it boils down to who can afford to run what is effectively siege warfare the longest.

would it be more costly for mars to invade earth or Earth to invade Mars under this scenairo?

[Temujin]

Picking the scenario of interplanetry warfare between earth and mars, both same tech.

Though, if earth maintained the same eco system and was maxed populated, whereas with Mars it has a number of domed colonies holding a populas that can support a war.

Without terraforming, Mars doesn't have worry about environmental damage; but they also can't put people out on the surface in tents if one of their domes gets damaged bad enough where life support fails.

Use of resources: if the conflict took place 300yrs from now would mars despite it's smaller size have the advantage of having more resources and material needed for construction, would earth's overpopulation be a major burden during the duration of the conflict? Would Mars in have a more structured planetry defence, due to it's size, and has two moons orbiting it compared to earth's one? Would a domed populas be better protected from chemical or radiation fallout from space by the weapons used from or fired into the atmospehre?

I can see Missiles being even more effective guided weapons, that can detect and evade incomming firepower from orbital defence or weapon platforms from the surface. Other then that it boils down to who can afford to run what is effectively siege warfare the longest.

Mars does have the advantage of being higher up on the Sun's gravity well, so they essentially have the advantage of holding the high ground. They are also nearer to a nice supply of asteroids that they can fling towards Earth.

would it be more costly for mars to invade earth or Earth to invade Mars under this scenairo?

All things being equal, its always easier to defend the high ground, thus I would give Mars the edge here; though I doubt either side could successfully invade the other.

[PeZook]

On one hand, the logistical support necessary for soldiers on Martian surface is going to be nightmarish, since they'll all need life support. On the other hand, Martians will either need to fight Earth armies in the field, thus taking the same disadvantage, or defend their domed colonies, in which case Earth can just threaten to breach the domes with artillery to force a surrender.

[Rossum]

Well, I would suspect that the Martians would have more advanced robotics than Earth... since they would need robots and automated systems in order to make use of the resources on their own planet. Trying to mine various metal ores and such would be absurdly more difficult for humans who need life support. I think most of their mines and factories and such would be operated by robots or automated systems while human overseers manage them from home where they have life support.

Without any native ecology, there would be no real environmental damage to be done so their mining operations would mostly be strip-mining to get the minerals. Dig huge pits, extract the valuable minerals, and dump the rest somewhere. Once they are finished extracting the valuable minerals from a pit they could build an airtight bunker in it, then cover the top. I think that partially underground structures would have an advantage due to additional protection against leaks (since micrometeorites might break through the martian atmosphere and hit buildings, and being underground would protect against temperature shifts that could result in cracking).

So, there would be plenty of underground bunkers that would be built as a matter of course. Or they could have large vehicles with long-term life support built in. Kind of like mobile homes, at the very least so that teams of workers can travel to the various automated factories to get close enough to work on them if they lose normal contact.



I'm imagining martian colonies to consist of domed airtight structures built on the surface because they are cheap to set up, underground bunker like structures that have additional protection from the uninhabitable surface, or walking cities which basically consist of a number of vehicles with built-in life support and some production capacity to act as mobile buildings, factories, and housing.

The walking cities would likely be used to set up fields of solar panels or the various stationary mines and factories. In the event of an interplanetary fight, a small percentage of the martian population would be essentially nomadic and it would be much more difficult to hit them with interplanetary missiles... if one of the walking cities was actually important enough to be targeted then the whole city could break apart into its individual vehicles/components, spread out, and then regroup once the bombing stopped.


I'm pretty sure that fielding infantry from Earth to Mars or visa versa would be highly impractical. People born and raised on Mars would be used to the lighter gravity and thus couldn't stand up in Earth gravity unless they had some serious assistance (either medical modification equivelent to making them Super Soldiers, giving them powered armor or exoskeletons, or having them all drive vehicles like Daleks). Earth infantry would have a slightly easier time but the psychological effect of leaving your nice, comfy, oxygen rich home to fight in some airless hellhole where you have to ration every breath or air and every once of water, not to mention the huge amount of time needed to travel between planets. Maritan soldiers might have a reason to go to Earth if they think they would enjoy a planet that is habitable for humans if they could handle the gravity thing.... though martians would be heavily outnumbered once they landed.

So, if you are planing to use infantry to invade another planet, then robots would sound like the way to go. They aren't weakened by exposure to microgravity and once you land on the planet you could set up a factory to build more of them. Invasions could include a few hearty humans who want to brave the trip who then command the robotic troops, some robot troops, factories and such to build replacements, and various weapons and equipment to help carve out a place for them to set up camp (most likely missiles and such to take out the numerous defenses set up to blast them out of the sky while on their trip). Cyberattacks and the like would play a significant part of the war, with one side trying to hack into and mess up the other sides computers and robots.