Imo the problem is that the planetary defence system is colony unique.  Devoting one tile to a planetary defence system won't really help you and I don't think it should because it's such a small sacrifice.

Building two side by side and putting them beside your colony capital would imo be making a more meaningful choice and would give you 40% planetary defence (50% with fortification) and 100% resistance which should be enough to make a difference if you have a high enough population on the planet (easier now since the population growth buff).

In theory that could lead to a planet covered in planetary defences that couldn't be taken by soldiers, but that would be a fair trade to me as long as an enemy could just wreck the planet from orbit to destroy the defences, which is sort of possible already.

I would also love if military starbases could boost planetary defence.  At least until mid to late game movement gets nerfed its not an effective strategy to garrison every planet that could be threatened, so if a military starbase could give ~50% planetary defence you could as long as you built planetary defences as well just garrison that starbase and force a fight to happen there.

Or even better (but harder to implement) let a fleet in a military starbase defend any planet in range of the military starbase as long as it has the movement to do so, sort of like overwatch in Xcom.

As long as the planetary defense score represents the fraction of the invading forces that are lost before the fight with the defending forces is resolved, this is not a problem. 100% planetary defense is sufficient for immunity to Conventional Warfare and Planetary Bombardment, 125% planetary defense is sufficient for immunity to Information Warfare, and 150% planetary defense is sufficient for immunity to Biological Warfare, Core Detonation, and Tidal Disruption. It is in fact extremely easy to achieve these values of planetary defense on selected worlds as long as you have a bit of elerium and two contiguous tiles*; making it easier to achieve these values by making the Planetary Defense System a repeatable improvement is not going to be good for the game.

As the Planetary Defense Dome grants 3 levels to adjacent improvements and has a functioning 5%/level planetary defense bonus itself, you could by the late game render every planet with 3 adjacent tiles immune to all invasion types if Planetary Defense Systems were repeatable even if the Domes were not - 50% from the Planetary Defense Dome + 2*10% from the Planetary Defense Systems + 2*5% from levels on the Planetary Defense Dome + 2*3*5% from levels on the Planetary Defense Systems + 10% from Military Specialization 1 + 10% from Fortification + 10% from the tech for Planetary Defense Domes + 20% from the specialization after Interstellar Democracy = 160% planetary defense; if the Planetary Defense Systems are adjacent to one another, that becomes 170% planetary defense and the specialization after Interstellar Democracy is no longer needed. If the Domes were repeatable, you'd need only two adjacent tiles for two Domes - 2*50% from the domes + 2*3*5% from levels on the domes + 10% from the tech for domes + 10% from Fortification = 150% planetary defense.

*An Elerium Defense Shield and Planetary Defense System which are adjacent to one another will provide 100% planetary defense total, if the Elerium Defense Shield is the only source of levels on the Planetary Defense System and the empire has no other sources of planetary defense bonuses. There are two early techs which each provide a 10% planetary defense bonus (the specialization after Militarization and the first tech in the planetary defense branch), and you can get an extra level on the Planetary Defense System for another 5% planetary defense by placing it next to the colony capital or military trade resource or on a tile with a military bonus (these three are preferable) or adjacent to a military academy (not as preferable since you need to spend an extra tile), and you can render your empire immune to Biological Warfare through the tech option; a further 20% planetary defense bonus is available in the Governance line of the tech tree for at least some factions, in the specializations after Interstellar Democracy. Upgrading the Planetary Defense System to a Planetary Defense Dome later in the game buys you a further 40% planetary defense, plus another 10% from the tech unlocking the Planetary Defense Dome. 120% planetary defense + immunity to Biological Warfare is trivially attainable with only two tiles and an elerium very early in the game, rendering colonies immune to Conventional Warfare, Planetary Bombardment, and Biological Warfare, and nearly immune to Information Warfare; with a very small bit of luck (for having a tile bonus granting military improvement levels or being adjacent to the colony capital or a military trade resource) or by investing an extra tile, that becomes 125% or more planetary defense, you can render a colony immune to every invasion type short of Core Detonation and Tidal Disruption long before those invasion tactics become available, and that colony can be made more than immune to those two invasion types at around the same time that those invasion types become available (Planetary Defense Domes can be developed at about the same stage of the game as either of those invasion types; a colony with 120% planetary defense using a Planetary Defense System will have 160% planetary defense after upgrading to a Planetary Defense Dome, or 170% if the 10% bonus from the tech unlocking domes is not included in the 120%). That's assuming that they haven't made the level bonus of the Elerium Defense Shield work; if they have made that work, then you can render your entire empire immune to all types of invasion with 30 levels total on Elerium Defense Shields in your empire, which can be attained with just 6 Elerium Defense Shields adjacent to Antimatter Power Plants, Planetary Defense Systems, and Military Academies, if you can place at least two of the Elerium Defense Shields on tiles giving bonuses to military improvements.

I'm not sure I understand you correctly.  Are you saying that they Elerium Defense Shields are suppost to give an empire wide bonus?  I'm looking at it in game right now and I don't see anything that implies that.

Also, I did mention that allowing better planetary defences would require a way to bomb the planet to rubble from orbit.

The problem with this "solution" to high planetary defense values is that I have no interest in reducing a planet to rubble. An asteroid field or class-0 world is of no value to me; a planet reduced to a low planet class and which cannot be restored to a higher planet class is of very little value to me. This defeats the primary purpose of an invasion for anyone who isn't just looking to destroy an opponent. Another objection is that it forces the factions of the game even further towards the genocidal end, or at least the end which isn't remotely bothered by inflicting massive civilian casualties on "them," of the spectrum; right now we can at least assume that the planetary population number represents military personnel (not unreasonable due to how invasion mechanics and troop transports work) or at least people engaged in military-related activities (virtually everyone represented in the population number apparently works in a state-operated lab or factory which works exclusively on state projects like warship construction and weapons development), which means that we can, if we want, still pretend to be playing "good" factions which restrict their attacks to valid military targets under the modern rules of war to the best of their ability - though the ease with which Information Warfare and Conventional Warfare, the two types of invasion which seem least likely to cause massive civilian casualties, can be rendered ineffective causes issues on that front even so.

Same reason I have no interest in Terror Stars* or other ways to destroy planets; if I do not get anything out of an attack against a planet other than a dead opponent, I'm really not that interested in making that attack, and a debris field just does not give me that much.

*It didn't help that Terror Stars were painfully slow and vulnerable in GCII and I typically played on Immense maps. Being painfully slow and vulnerable meant that Terror Stars were probably more effort to use than invasion transports and provided less gain, which meant that aside from the novelty value or being spiteful they held little attraction.

To be perfectly honest, I don't believe that that's a bug that should be fixed. An empire-wide planetary defense bonus that stacks the way that planetary defense bonuses currently do which is as widely available as that one can be is a very, very bad thing for the game, especially since there's no way to shut it off - you don't lose the bonuses of things that require strategic resources when you have less of that strategic resource than you need, and unless I can culture-flip a planet invasion is the only way I can take a colony. If they fix the issue with improvement-granted empire-wide planetary defense bonuses, the Elerium Defense Shield's level bonus needs to be changed to be something other than that (planet-specific is okay, though it makes it even easier to render specific planets immune to invasion until the late game as you no longer need an extra level on the Planetary Defense System for immunity to Information Warfare in the early game); empire-wide invasion immunity with relatively little investment is not a good thing, and very little investment is required if you're playing on one of the larger maps with relatively low numbers of opponents and relatively high numbers of useful planets (especially since with more planets there are more chances to find really good spots for stacking military levels; I don't think it's that uncommon to have a military tile bonus adjacent to a trade resource which grants military levels, though it's also not that common, and I've occasionally had planets which had two such trade resources adjacent to the tile which grants +3 military levels as well as four other adjacent tiles which I could either build in immediately or terraform to be usable).

That depends on how willing people are to use nuclear, biological, and chemical weapons. WWI introduced chemical weapons and WWII is widely regarded as having been a total war, and yet chemical weapons were not widely used in the second world war despite both sides having access to and reasonably large stockpiles of chemical weapons and despite both sides being reasonably willing to bomb cities into piles of rubble.

Great, synopsis Naselus. I figured it was along these lines. on Normal or Gifted I have never seen an invasion fail against the ai. 

Hmm...

I asked:

Would you like more effective PLANETARY DEFENSES in GalCiv3.

You wrote:

You can alway put a fleet into the orbit of the planet instead of using ineffective PLANETARY DEFENSES.

I cannot see any contradiction. I did not ask whether it is possible to use something instead of ineffective PLANETARY DEFENSES as they are in the game.

You should read more carefully before you write an answer that does not fit the question.

From what I have read 'into' Frogboys expand-alone it will fundamentally change the entire game. It will likely be very close to GCII in how we assemble ships. 

No longer will we be able to stack many sensors and engines on a ship without sacrificing space for weapons or defenses. 

I am looking forward to the expand-alone. I will PERMANENTLY remove the wheel and change how we build our ships from that point. 

1.

Well, that depends on how much ships you will need to overcome planetary defenses.

If, for example, planetary defenses are able to inflict at least some losses to an attacking small or medium-sized fleet, this will reduce the advantage and speed of an attacker.

It would also make it impossible to send off an armed transport or a transport an two or three tiny ships to capture a planet on their own.

However, it will not (and should not) prevent you from sending five capital ships before you send in your transports.

2.

In my opinion those "fast transports" should be nerfed too.

It is simply ridiculous that engines  do stack. This is simply wrong. Using two or three engines will not allow you to be two or three times as fast as before (as is proven by simple physics).

What is more, it is likely, that your ship will not be able to stand the force of additional engines without changing the design of the ship (additional stabilizers, walls and so on).

Last, but not least, it is simply bad game design to allow people to min/max their ships in such a way. It leads to "gamey" ship designs. No real general will decide that he wants tanks that do not survive a single enemy hit, even if this allows for greater speed of movement or for more weapons, because it will be catastrophic for the morale of your troops.

In GalCiv3, you can "throw away" the lives of your space-pilots without any thought. Simply build new ships and recruit new troops. Nobody will ever ask what happened to the old ones.

2-3 ion drives is not 'stacking engines'. 10 ion engines is.

I do not consider stacking engines an exploit or a problem. On Insane maps even having 3 Stellar Folders is ONLY about 21 hexes (7 per engine). That is a PITIFUL distance on an Insane map. Same goes with sensors but I know we had a discussion on that a year or so back. The Stand-alone will redesign all (equip-able) parts with both a base mass size and a (percentage) increase which means we can stack all the engines but it will greatly diminish the available space for other components. More Stellar folders take up more and more space after the first one. 

This would also mean fewer weapons and armors (if they add a mass-size-percentage increase) to those things.