Semi-Viable Mecha Idea?

[RedImperator]

In some hypothetical scenarios, it may be that just about any large armored vehicle gets zapped from orbit by the side with domination of space, whether tanks or mecha. Potential beam weapons running on the power from nuclear reactors on a space warship wouldn't run out of ammo, able to kill tanks all day long.

To quote a wise man, I'm smelling a whole lotta "if" coming off this place. The way I see it, if one side gains total domination of space, the war is over anyway (well, the part involving tanks is; insurgencies are, as always, another story). If control of space is contested, these killer satellites are going to be target number one for both sides, and their numbers are going to plunge, making tanks viable again.

There is nothing that says the whole mecha needs armour against anything but small arms. This is mainly as if you can't use a tank you only need to beat grunts.

Actually, the mecha do need to be heavily armored, or else they're going to get slaughtered my man-portable antitank weapons and possibly lighter, dedicated anti-mecha weapons. Not to mention the effects of mines and IEDs. I've made this point once already in this thread: this is not World War One, and the infantry, when faced with light armor, has options besides "shoot at it with rifles" and "run away screaming".

[Fingolfin_Noldor]

The trouble really with mecha, is that the ability of mecha to carry heavily armor is second to a heavy main battle tank, which has the advantage of a having two big tracks that can ensure it has low pressure to ground ratio, and carry a big gun. Really, a mecha is bloody overrated, beyond it's cool looks.

[Commander 598]

I think the issue that most Tank Lovers have with Mecha is that Mecha are made out to be superior weapon systems in every way without any logical reason for it.

I think this is mostly just what some individuals perceive. If we ignore the HAX machines, the mecha of most real robot franchises is rarely if ever portrayed as superior to tanks...perhaps the 'verse in question's tanks (Gundams tanks are basically HURR thanks to several factors and most of Zeon's early advances seem to be thanks to zerg rush landings on top of Fed airbases) but not actually "superior" to conventional systems (IIRC, Gundam again, probably about 75% or more of the Fed's forces at Odessa were conventional vehicles, and they won). They're mostly just good enough to kill things and not die doing it half the time. Even as far off as V Gundam the mecha were still getting pasted by conventional units despite the fact that almost all of them possessed energy shields and could practically fly on thrust alone.

Actually, the mecha do need to be heavily armored, or else they're going to get slaughtered my man-portable antitank weapons and possibly lighter, dedicated anti-mecha weapons.

Man portable anti-tank weapons kill armored vehicles all the time, why do mecha need to be invulnerable to them? And most light armored vehicles are only armored to protect against 14.5mm HMGs at best, IIRC.

[Darth Raptor]

You could have them big in order to accommodate the power plant, not the armor. Future point defense will probably counter heavy weapons more effectiely than future armor. And the inability to lug around a 150mm cannon doesn't mean you're stuck with machineguns. There's missiles, directed energy weapons and, obviously, recoilless rifles.

[Fingolfin_Noldor]

You could have them big in order to accommodate the power plant, not the armor. Future point defense will probably counter heavy weapons more effectiely than future armor. And the inability to lug around a 150mm cannon doesn't mean you're stuck with machineguns. There's missiles, directed energy weapons and, obviously, recoilless rifles.

Erm... how do you plan to handle an Depleted Uranium APFSDS round traveling at nearly 2000 m/s or more?

[RedImperator]

Actually, the mecha do need to be heavily armored, or else they're going to get slaughtered my man-portable antitank weapons and possibly lighter, dedicated anti-mecha weapons.

Man portable anti-tank weapons kill armored vehicles all the time, why do mecha need to be invulnerable to them? And most light armored vehicles are only armored to protect against 14.5mm HMGs at best, IIRC.

Just for fun, why don't you quote the part of my post where I said they had to be invulnerable? What I did say was that they needed to be protected against heavier weapons than small arms, or else you'll see a repeat of the unarmored Humvee fiasco with vehicles that cost ten times as much. And even with that, you'll never be able to armor one as well as a tank, meaning an RPG which would bounce right off an Abrams will one-shot kill a mecha, which is critical, because I've seen nothing at all to suggest in this thread (or any of the dozens of other mecha threads we've had on this board) that a mecha would be any less vulnerable than a tank in urban combat. And as for all of those other armored vehicles that man-portable anti-tank weapons kill, every last one of them is cheaper, less complex, more versatile, better protected, and has a lower profile than an equivalent mecha, which brings us right back to the fundamental question: why bother with the damn mechas?

[Oskuro]

I my own fiction, I have this evil race of cyborg things using walkers for three roles:

a) A larger version of the basic soldier, meant for close quarters indoor fighting (Somewhat like a middle ground between a Wh40k Terminator and a Dreadnaught)

b) As platform for Artillery/AA guns that require to negotiate extremely harsh terrain, but that do not get (should not get) in the line of fire.

c) As the Titan-sized robot of DOOM(tm) wich I've included merely for the awesome factor.

The rest are cyborg tanks, gunships and infantry.

[Admiral Valdemar]

Fuck mechas. Robots, people.

You don't replace the tank, you complement it. Why get something to do what an MBT already does well enough? Again, if Sikon's scenario appears, with warships in orbit keeping heavy armour at bay and fending off any other orbital transgression, then you need not worry about facing tanks anyway. It'd purely be lighter, faster and smaller vehicles and infantry be they augmented or not.

[Sikon]

In some hypothetical scenarios, it may be that just about any large armored vehicle gets zapped from orbit by the side with domination of space, whether tanks or mecha. Potential beam weapons running on the power from nuclear reactors on a space warship wouldn't run out of ammo, able to kill tanks all day long.

To quote a wise man, I'm smelling a whole lotta "if" coming off this place. The way I see it, if one side gains total domination of space, the war is over anyway (well, the part involving tanks is; insurgencies are, as always, another story).

The war is likely over aside from what can't just be blown up from space, which may include fighting to take any valuable and civilian-filled locations like cities that the victor may not necessarily want to just level. But that's exactly the context of the last part of my post.

The enemy really doesn't have much hope of true victory at that point, but history demonstrates frequently continuing fighting down to the level of infantry insurgencies, so military hardware for combating such is likely to get built.

If control of space is contested, these killer satellites are going to be target number one for both sides, and their numbers are going to plunge, making tanks viable again.

Effective stealth in space is unlikely, and there is no cover, along with extreme engagement ranges for the weapons on space warships (a lot more than the term mere satellites tends to connotate, once there is a space civilization and manufacturing). As a result, there is not particularly likely to be a bunch of space warships around earth shooting at each other for months straight while tanks could fight other tanks unmolested on the ground.

Rather, after such a rapid engagement with no hiding from it possible in space, wiping out one side in the vicinity of the planet, the other side has surviving ships in the region, and they fry targets on the ground for the rest of the war. For advanced civilizations, the space war would tend to be dominated by such an engagement with space hardware fighting other space hardware, without ground weaponry being comparatively effective.

Given enough advancement, missiles launched from ground at space warships tend to be detectable and fried during their boost phase through the atmosphere, given their several disadvantages which are huge in combination:

• Maximum speed of a few km/s when going up through the atmosphere to not burn themselves up, due to air resistance, while moving at a small fraction of a km/s initially as they accelerate from rest.
• Obvious targets, impossible to hide when the heat of high-velocity passage through the atmosphere and their rocket exhaust gives them away during their boost phase.
• In an advanced future situation, they're not facing the equivalent of a small number of tons of 1980s-style Star Wars program proposal space weaponry launched at an expensive thousands of dollars / kg but still potentially wiping out a whole force of ballistic missiles. Rather, they're facing even far more. The number and mass of rockets able to be affordably constructed and launched at a single time will tend to remain somewhat limited, yet it is literally orders of magnitude less than the mass and quantity of space hardware able to be built pre-war from extraterrestrial materials after mass driver launch of initial hardware over a period of years.
  
  As a loose analogy for the general principle, the 1975 NASA space station study had a 10-million ton spacestation made for a fraction of a trillion dollars with usage of extraterrestrial materials and lunar mass drivers in that case, yet launching the same mass from earth with current $10000/kg rockets would cost $100 trillion, so much orders of magnitude different as to not be competitive. Of course, future rockets could be far less expensive, for reasons discussed before elsewhere, but it is also the case that usage of extraterrestrial materials could be expanded far more too.
  
  The general situation is that anything in space made over a period of years can be orders of magnitude bigger and far better than anything reliant on a single day's rocket launch from the ground, whether civilian or military, whether in the near future or the far future.
  
  It's possible to have millions or even billions of people living in space with up to billions of tons of total equipment manufactured from extraterrestrial materials, without having any more earth-to-space capability than such as a mass driver and rocket system sending up cumulatively millions of people per year but doing so only through a figure on the order of 0.00001 billion tons able to be sent up per day.
  
  Even for such a vast space civilization, the capability is never needed for more than a few thousand tons per day launch capability off earth, and it may or may not ever be obtained when the key is rather to have such add up over thousands of days, over a period of years, then leverage it into orders of magnitude more extraterrestrial material usage.
  
  Even in an era of many large space warships, actual rocket launch and missile launch capabilities from earth can remain limited and subject to the usual difficulties, thus giving the advantage to hardware already in space prior to the war.
  
  Of course, in this context of rockets and mass drivers, I'm not considering magic-tech drives like those of soft sci-fi for planet-to-space launch, but this is assuming a fully hard sci-fi scenario with no antigravity loopholes in known physics, materials restricted to the limits of the elements in the periodic table, and so on.

A ground beam weapon facility large enough to truly threaten the space warships could end up massing hundreds or thousands of tons, a large enough concentration of metal to be detectable wherever it was on the planetary surface if there were advanced sensors as described in the last post. If someone nevertheless builds such, the likely tactical response is to have space warships stay at great distance out of its effective range initially, to ensure it is destroyed before moving close to the planet afterwards.

While there are multiple potential counters to such, one of the simplest may be to fling a chunk of asteroid metal at that location from long distance, since, even if some of it is disintegrated, the high-momentum debris still impacts. (A big global civilization-destroying asteroid isn't needed, just a relatively small impact to take out the facility). Nobody has ever seriously proposed trying to destroy an incoming asteroid with lasers. That's for good reason.

In contrast, it is relatively conceivable to eventually develop massive beam weapons like ones of hundreds or thousands of tons mass able to destroy smaller multi-ton targets like an enemy tank in a matter of seconds or less. Such requires the equivalent of the vaporization energy of only a few kilograms, as disintegration of part of something requires orders of magnitude less energy than truly vaporizing it.

(This is something not understood by most sci-fi fans, but, for example, a typical nuclear blast underground will truly vaporize only thousands of tons yet disintegrate millions of tons because the energy requirements per unit mass are orders of magnitude different, and the same applies with any explosion, such as how one pound of dynamite can't vaporize much but can be emplaced in mining to disintegrate hundreds to thousands of pounds of rock).

However, what if that very same massive beam weapon is applied against an incoming chunk of asteroid metal massing up to thousands of tons if necessary? With it only vaporizing kilograms a second, it doesn't tend to get time to do much when the speed of such means that incoming object goes from hundreds of thousands of kilometers range to impact in a matter of seconds.

Anyway, the net result is the side winning the space war is unlikely to be effectively opposed by ground weaponry. They soon end up being able to destroy their opponent's tanks on the surface, resulting in the situation becoming a matter of fighting over only what can't be just blown up from space, like fighting enemy infantry and insurgents in cities desired to be taken intact ... the scenario of the end of my past post.

Of course, also in a lot of scenarios, one side has a clear advantage from the start, almost automatically soon reducing enemy resistance to infantry insurgencies, a future equivalent of U.S. versus Iraq.

[chr335]

The only reason I can think of for developing a walker is for quick movement over rough terrain which modern wheeled and tracked vehicles can't do yet.

[weemadando]

The only reason I can think of for developing a walker is for quick movement over rough terrain which modern wheeled and tracked vehicles can't do yet.

And that's why you have airlift capability and man-pack weapons...

[Admiral Valdemar]

Even for city insurgencies, a suitable warship in orbit would be able to lay down fire suppression unmatched by any unit at ground level. A lower power setting on the laser/particle beam would allow guerilla positions to be attacked with pinpoint accuracy. The ability to incinerate a single person, or several in rapid succession, should not be difficult for any system that acts as CIWS for the vessel and is expected to take out multi-tonne missiles on intercept courses. The use of "Rods from God" and other kinetic harpoon concepts would allow for wider area denial, or allow the rapid deployment of MEMS sensor clouds or NBC munitions.

Given enough ships and a competent military command, then nothing should touch that ortillery fleet. This is somewhat analogous to some series of Mobile Suit Gundam with the typical space colony exiles developing their forces in space at Lagrange point positioned O'Neill Island-3s and lunar or Martian colonies etc.

[Bounty]

The only reason I can think of for developing a walker is for quick movement over rough terrain which modern wheeled and tracked vehicles can't do yet.

What makes you think legged vehicles would do any better? Building walking vehicles is something that rarely even tried precisely because it's so difficult to get the moving even over flat terrain. Humans can crawl over obstacles a wheeled vehicle might not be able to cross, but we've got millions of years of evolution under out belt to fine-hone our balance and sensory feedback. Reproducing that in a machine... well I suppose you've seen ASIMO?

[Admiral Valdemar]

I do not see the pointing to ASIMO as a refutation of machines being able to navigate harsh terrain. I suppose you've seen Big Dog?

Even if it's difficult, that is by no means an argument against it. It is clear that a properly developed A.I. in an aircraft would beat any human pilot with a near 100% success rate given the advantages a UCAV has over an aircraft piloted by a biologic. We don't have them now, but developing them is the hard part. Same with walking machines. There is no major obstacle once a suitable control system is in place, and indeed, we already have machines perfectly able to navigate such obstacles that can be smaller than upright humans and carry far more in terms of ordinance. Legs are highly versatile, or leg analogues like the TETwalkers NASA proposes for exploring Mars.

The concept of swarm robot hunter-killers is useful, given cheap, easily produced machines able to navigate any terrain would be far more useful than any standard infantry unit. Even if each individual unit was less durable than your average grunt (doubtful), they could be mass produced and enjoy economies of scale, something humans cannot benefit from without clone armies which breaks all sorts of ethics codes for state militaries.

Today, such machines exist in the form of SWORDS, but they are simply baby steps towards fully autonomous combat vehicles able to match any human in whatever attribute you wish to compare them against.

[chr335]

The only reason I can think of for developing a walker is for quick movement over rough terrain which modern wheeled and tracked vehicles can't do yet.

And that's why you have airlift capability and man-pack weapons...

Depends on the terrain but in most cases your right.

[Bounty]

I do not see the pointing to ASIMO as a refutation of machines being able to navigate harsh terrain. I suppose you've seen Big Dog?

I have - only on flat terrain, though, not going over obstacles. I admit I was mostly thinking about bipedal walkers, versions with more legs will obviously be more practical.

[Admiral Valdemar]

I have - only on flat terrain, though, not going over obstacles. I admit I was mostly thinking about bipedal walkers, versions with more legs will obviously be more practical.

Fairly old video. Possibly advanced far more than that now. Quadrupeds would be more stable, but bipeds have a smaller footprint. It's not unreasonable to have one maybe perform in both configurations, depending on mission. All that is really lacking is the brain after the mobility is sorted out (a power source would preferably be a fuel-cell, supercapacitor or micro-turbine).

[Ford Prefect]

Erm... how do you plan to handle an Depleted Uranium APFSDS round traveling at nearly 2000 m/s or more?

Err, you don't. This isn't just a mecha thing, either; the main guns used on modern tanks will, as I vaguely recall from threads on the subject, can reliably penetrate the armour of the the tanks that use them. As I recall, anyway, if someone would like to correct me, that would be nice.

[Sikon]

Even for city insurgencies, a suitable warship in orbit would be able to lay down fire suppression unmatched by any unit at ground level. A lower power setting on the laser/particle beam would allow guerilla positions to be attacked with pinpoint accuracy. The ability to incinerate a single person, or several in rapid succession, should not be difficult for any system that acts as CIWS for the vessel and is expected to take out multi-tonne missiles on intercept courses.

Yes. After taking out priority targets, the ships are still in orbit and may have reactor power for their weapons indefinitely, so they might as well help out against lesser targets too.

Where the weaponry of ground forces like infantry soldiers or robots could be more needed directly might be when one or more of the following several circumstances applied:

• Fighting inside city buildings with collateral damage concerns:
  
  Let's say there are insurgent enemy infantry hiding inside a building, while friendly soldiers or robots are clearing from room to room, holding their fire when they met non-combatants but taking out opposition. Orbital fire support technically could blast through the roof of the building or irradiate those inside. However, while sometimes that might be done, often it wouldn't be an acceptable option.
• Too many individual minor targets or difficulty finding them all, especially depending on the size of the fleet and if under time constraints:
  
  For example, an advanced ortillery fleet should be able to wipe out 1000 big enemy tanks / armored vehicles in a short period of time, but it may or may not be big enough to also take out 1000000 individual enemy soldiers or small cheap enemy infantry robots anytime soon. Or the latter may successfully hide from sensors sometimes. How many targets the fleet can aim at, fire upon, and hit per minute, per hour, and per 1400 minutes in a day may be high, possibly even high enough to mostly do both, but who knows?
• Situations where non-lethal or less-lethal weapon capabilities are desired:
  
  If blowing something up is the goal, ortillery works fine for it. If something needs to be captured or needs finesse like riot control, ground forces can be particularly needed. Ortillery could optionally perhaps also include narrow-beam EMP capabilities, microwave MASERs, wide-beam illuminating and dazzling lasers, or deploy warheads with various types of submunitions. However, still, it is usually most suited for being a lethal and highly destructive weapon system.
  
  Even today, military R&D has looked into a non-lethal microwave weapon mounted on a jeep, investigated dazzling lasers causing non-permanent effective blindness, and experimented with sticky foam guns, aside from the now frequent usage of electric tasers in policing, among other possibilities.
  
  Non-lethal weapons may actually become far more often utilized in the future once there are infantry robots. Militaries are currently pretty hesitant to deploy non-lethal weapons since their reduced effectiveness tends to put soldiers using such at a disadvantage. For example, issuing one's own soldiers only TASERs and telling them to assault an enemy firing AK-47s and throwing grenades wouldn't make sense, after all. In occupations and policing, they may like to have non-lethal options, but rarely are they willing to put the lives of their people at much extra risk only to capture enemies alive or reduce the number of non-combatants killed.
  
  However, future expendable hardware might more often be risked. Even capturing someone with a tranquilizer dart injection taking a number of seconds to spread through his bloodstream (like large animals are captured today) may become more often a realistic option if it was safely delivered by a long-range robotic miniature antipersonnel missile, for example.

Outside of the preceding situations, the ortillery might have close combined arms ties for infantry support. Sometimes, in addition to the ship's own imaging capability and that its deployed sensors, a soldier or robot might aim a weapon that doesn't just fire a bullet directly but causes orbital fire to destroy the designated target, even sometimes in counterinsurgency warfare when appropriate, like enemies hiding behind cover. That could give his "rifle" with a small designator relatively unlimited effective firepower, perhaps as high as desired up to almost anything short of a nuclear blast.

[Sea Skimmer]

First up I am a fan of mecha. Second I'm a tread head. Since that is covered, most of the time the rationale for "realistic" mecha is that they are built for terrain hostile for a tank, in other words where you would like to use a tank but can't. Secondly the bitching about armour only applies if you think like some naval firms and armour everything, you just armour the body / cockpit and let the other stuff get shot off ... if your defense is not to get shot that is .

That’s a very poor idea for land warfare when you might have to advance through an artillery barrage, or encounter a roadside bomb that sprays you with fragmentation.

American battleships and tank destroyers were designed along these principles of only armour the stuff you need to.

Battleships have limited armor envelops because they weigh 30,000 tons or more and you have no choice. Everything important was still armored anyway, and the armored envelope was designed to encompass enough tonnage that flooding the soft ends, which held nothing important, wouldn’t sink the ship.

Any sane sized mecha is just going to be fucked by any penetrating hit because it’s not big enough to have any redundancy like a warship can. I don’t know what gave you the idea tank destroyers aren’t fully armored, they most certainly are except the roof. The lack of an armored roof was quickly found to be a mistake, as was the entire tank destroyer concept and the Army began fitting lids over the open turrets rather quickly. Then it stopped building them entirely. Great comparison, mecha vs. a flawed and failed land weapon that only one nation fielded, then killed off.

You can even go as far as the whole B25 lets see what comes back shot up and armour the other sections idea if you want, base it round a experimental unit. There is nothing that says the whole mecha needs armour against anything but small arms. This is mainly as if you can't use a tank you only need to beat grunts.

WW2 aircraft were cheap and got blown away and expended like rounds of ammo, no one is going to build a ground vehicle with that kind of mentality. It just doesn’t work if you have to go on the attack, unlike AA guns a ground defence isn’t passed by in seconds, it will just plain annihilate you if you can’t survive hits from its weapons.

[Fingolfin_Noldor]

Erm... how do you plan to handle an Depleted Uranium APFSDS round traveling at nearly 2000 m/s or more?

Err, you don't. This isn't just a mecha thing, either; the main guns used on modern tanks will, as I vaguely recall from threads on the subject, can reliably penetrate the armour of the the tanks that use them. As I recall, anyway, if someone would like to correct me, that would be nice.

Does it matter? If you can't even stand up to a round like that, then Mechas are an even worse idea than tanks, because of the complexity involved in constructing those things. At least tanks can be mass produced relatively cheaply.

And there are ways to defeat an APFSDS round. It's called heavy ERA. The Russian Kontakt-5 ERA was known to be able to defeat the late 1980s US APFSDS rounds.

[Ford Prefect]

Does it matter? If you can't even stand up to a round like that, then Mechas are an even worse idea than tanks, because of the complexity involved in constructing those things. At least tanks can be mass produced relatively cheaply.

I'm not arguing for the practicality of mecha here (there's no such thing), I am simply pointing out that your example is a poor one. It's essentially irrelevant; there are a lot of reasons why mecha are not a practical military weapon, beginning with engineering complexity and the fact that no recognisable role exists for a ten to twenty meter tall robot. You would, for example, have a point someone had said 'hurr, mecha can replace tanks'.

Admittedly, you are attemping to counter thei dea of point defense becoming more effective, but at the end of the day, point defense does not have to perfect, it just has to be effective. And if it is not effective against tank cannons, then clearly it is not a technology to be relied upon when facing tanks.

[Sikon]

Although future armor performance will increase, so too will the penetration capabilities of future warheads. Since those effects may perhaps largely counterbalance each other anyway, let's use the relative performance of current armor versus current warheads for an illustration.

In a way, one can divide current armor protection into three general categories:

• 
• 1. Heavy armor, enough to stop even the best modern RPGs which can penetrate up to 700mm RHA-equivalent:
  
  Similar to this level of heavy armor protection exists about nowhere except on main battle tanks, not on the Bradley IFVs or anywhere else, while, even then, it only exists on the tank's front (and sometimes side) armor due to weight constraints.
  
  The M1A2 has 800 mm to 1600 mm RHA-equivalent protection on its front. Naturally, such isn't provided by literally 0.8-m to 1.6 meter thickness of rolled homogeneous steel armor but rather by a few inches of composite armor which gives the equivalent effect against HEAT warheads, much more effective per unit thickness and per unit mass. However, to keep the tank's weight from rising far above its current 70 tons, top and rear armor is vastly thinner. (Exact figures aren't easy to look up, but all MBTs are similar in that regard, like a several centimeter or less T-90 illustration). The side armor is an intermediate thickness.
  
  For perspective, even the Bradley IFVs only have on the order of 130mm RHA-equivalent armor on their front and less elsewhere. That's an order of magnitude different from the preceding heavy armor category, analogous to how the rear / top armor even on the M1A2 is around an order of magnitude less than its frontal armor thickness equivalent against HEAT warheads.
  
  
• 2. Light armor: 10-150 mm RHA-equivalent, although able to be provided by a lesser thickness of more advanced armor than RHA:
  
  Such stops bullets from AK-47s and provides some shrapnel resistance. That towards the upper end of the range can stop armor-piercing heavy machinegun rounds or even autocannon fire while that towards the lower end does not. No armor in this thickness range can reliably stop the penetration of the best modern RPGs, which can penetrate vastly more as previously mentioned, up to 400-700mm RHA-equivalent.
  
  Most armor on most vehicles comes into this general category: all the armor on Bradleys, Strykers, etc. plus even the rear and top segments of main battle tanks.
  
  One of the most common military vehicles in practice, the 20000 Humvees in Iraq would also be in this category except many of them don't even have almost any armor, a particular source of vulnerability which has been worked on with 1 ton or so of armor added on some to be an improvement.
  
  Light armor means relying on not getting hit by any of the better modern portable anti-tank weapons.
  
  
  
• 3. Active protection systems
  
  This is a whole alternative approach, to defeat RPGs and missiles by good enough electronics to detect the incoming projectiles and blast them, rather than expecting thick enough armor to physically stop them. An example is the new Trophy system starting to get deployed now.
  
  Vastly more advanced future technology would no doubt mean far greater capabilities. If anything, this can advance much more than physical armor alone can improve in a hard sci-fi scenario. Although some further materials improvements are possible, physical armor can't have orders-of-magnitude improvements when still limited to elements in the periodic table.

Observe the frequency of armor in the 10-150mm RHA-equivalent range versus the relative rarity of equipment armored with 800+mm RHA-equivalent thickness. Often armor in between those thickness extremes isn't bothered with as much today,* since there can be limits to the utility of armor thick enough to be very heavy yet meanwhile still too little to stop the better warheads anyway.

* (Outside of the side armor of some modern tanks expecting often glancing impacts).

Right now, modern electronics and related technologies have not quite yet advanced enough for the average cheap infantry-fired anti-tank weapon to seek out and hit the rear or top of a tank. However, there is probably only a matter of time before such becomes increasingly prevalent, though. Even already, the recent U.S. Javelin antitank missiles are fire-and-forget with a top-attack mode to hit the top and penetrate the armor of any tank in the world.

So what is the future? Is it that of today's MBTs with heavy armor on their front and sides but light armor on their top and rear? If smart top-attack portable anti-tank warheads become common enough, trying to have the heavy armor method work reliably might mean eventually having to armor the top and rear heavily too.

(This is even just considering fighting against infantry weapons for the moment, neglecting alternative scenarios like that discussed in prior posts where the side who lost the space war gets their tanks fried by space warships, not that any practical thickness of armor would help much against such).

What if super-heavy tanks were made with full thickness heavy armor on all sides, rear, and top? Ordinarily, that would mean tanks of maybe something like 150+ (?) tons each instead of 70 tons, which carries its own wide set of disadvantages though it is technically possible. If tank crew space could be reduced with fewer people than having 3 or 4 inside, or if the tank could be made robotic and unmanned entirely, then its volume, area needing armor, and resultant mass could be decreased.

It might maybe be possible to keep an heavy armor approach viable by means such as instead robot tanks with very high power-to-volume engines, no bulky air-filled crew compartments inside, and everything made to allow a relatively enormous fraction of their total volume to be pure armor, compared to current tanks. Otherwise, top-attack smart munitions may be quite an issue.

An alternative and very likely potential option is to often give up on #1 while focusing on #2 perhaps supplemented with #3 as well.

If one doesn't expect to have heavy enough armor to directly stop 700+ mm RHA-equivalent armor-penetrating warheads hitting the top and rear anyway, an option is to just go for far lighter armor in the 10-150mm RHA-equivalent range, protecting against small arms fire and most shrapnel, perhaps combining with active protection systems against those infantry missiles.

The most extreme version of that scenario would be vehicles with heavy physical armor as their focus being perceived on future battlefields almost like knights in plate armor are considered today, with a dominance of light armor and active protection systems over relying on heavy armor. It's not a guaranteed scenario since heavy armor might remain viable in some applications especially with the possibilities discussed before, but it is one realistic possible future scenario considering how much missiles tend to get cheaper, smarter, better, and more relatively numerous.

So, although the future would appear to belong far more to hordes of robots, missiles, orbital fire support, and infantry rather than mecha outside of specialty roles, relative appropriateness when considering having a few mecha could be to think of them not as a heavily-armored MBT equivalent, something for which their geometry and surface area isn't ideal anyway but rather perhaps joining IFVs and light tanks as among classes of light armored vehicles with active protection systems.

[Darth Raptor]

Does it matter? If you can't even stand up to a round like that, then Mechas are an even worse idea than tanks, because of the complexity involved in constructing those things. At least tanks can be mass produced relatively cheaply.

*COLOSSAL SIGH* I was addressing the point that mooks on foot could bring them down with heavy infantry weapons (namely missiles and rocket-propelled grenades). Obviously, it's not god mode, and obviously (to everyone but you tank crusaders, apparently) no one is disputing that tanks are overwhelmingly superior to mecha which I and everyone else ITT readily concede are utterly infeasible. You guys are preaching to the converted and frankly, it's just an itty bit irritating. How about instead of flogging that dead horse some more you try and participate in the spirit of the thread? You know, suspension of disbelief? In this genre, we've got mecha, so try and figure out why. Justify their already established existence. Starfighter threads rarely devolve into such tedious bash fests and they're a fundamentally broken idea too. It's pointless to keep harping on how much starfighters and mecha suck because people like them and thus will use them in their fiction.

[Sikon]

Adding a little to the prior post, to ensure there isn't a misconception that advanced active protection systems could only engage missiles and not do anything against incoming cannon rounds:

Actually, rather, such might take out large incoming high-velocity projectiles too if the technology is refined enough:

Conventional wisdom for some time has been that active protection against KE penetrators falls in the “too hard to do” category. Because the penetrators are moving so fast, the acquisition, detection, intercept, and destruction must occur within extremely minute timeframes. Then again, the Army Science Board is optimistic and believes that a practical system could be demonstrated within the next few years.

The Board bases its optimism on two beliefs: 1) that sensor requirements to detect and timelines to intercept are reasonable given projected technological advances in the industry, and 2) it believes explosive perturbation of the long rod’s trajectory can cause it to miss the intended target. The ASB concluded that APS could provide excellent protection against KE penetrators except within certain ranges. For KE penetrators, that would be on the order of 500 meters and for handheld HEAT it may be as little as a few tens of meters.

The above is an illustration from an U.S. Army colonel's paper here.

When such technology is bordering on almost practical even now, the likelihood of such capabilities existing when technology is advanced up to one or more centuries beyond now should be far higher. Indeed, even the range limits would vary and be improved if technology was far more advanced than contemporary.

If electronics and related technologies advance enough while materials tech can not improve more than a relatively limited degree (still constrained to real-world elements in the periodic table), the ratio of the effectiveness of heavy physical armor to that of active protection systems tilts more and more in favor of the latter.