advice on assaulting planet?

My suggestion, do little/minimal changes to default strategies, such as whether to have auto-launch on or off. Easy to undo stuff.
Best to just copy the one you want to alter, and then edit the copy.

There is a Save Strategies option, although I think it saves all your stragies, default and custom.

If you messed up a default strategy, and have no backup, I have an idea that might work. Just quick start a single player game, save the default strategies, maybe name the file "Default Strategies", then quit the new game, go back to the game you were playing, and load the 'backup' to overwrite the messed up strategies with the default ones. Then redo your custom strategies and make another backup, such as "My Strategies 001" or something like that.

Two things I wish to point out under Strategies, under Target Type Order and Settings.

Engage Range:
Do Not Engage can be handy if you don't want certain targets attacked at all.

Damage Amount:
100% by default, also has 90%, 75%, 50%, 25%, 10%, All Weapons Gone and All Engines Gone.
Very handy options.
All Weapons Gone should be just the thing for strategies meant to support planet capture, have one fleet on capture planet, and a fleet of faster ships (at least faster than the troop transports) with Planet with Colony as the top priority and with All Weapons Gone for Damage Amount.
(possibly run simulations first to be on the safe side to make sure it works)

Planetary Napalm and hefty defenses might also be handy for a colony defense clearing ship, especially when dealing with planets with lots of weapon platforms.

I would recommend good troop transports, be they freighters, carriers, or regular ships with some cargo bays.
Good defenses a must, weapons are a secondary concern, at least a few PDs a must, especially if you enemies uses lots of seeker weapons, fighters, sats and/or drones.
If a capture planet ship is equipped with fighter bays, make sure capture planet strategy has auto-launch units off so they can deliver fighters to the enemy planet.
Their main goal, IMO, is simply to last long enough to deploy forces to a planet. If they get blown up afterwards, oh well, it just means you are stuck for a little while with extra troops/fighters to protect the planet from enemy counter attack.

Personally I use 2 or more squads with my fleets.

Fleet strategy - Capture Planet.
Task force 1 - Capture Planet (Slower Movement)
Task force 2 - Maximum weapons range - Missile assault
Task Force 3 - Close combat assault.

If TF2 and TF3 are faster than TF1, then they should be able to clean up a lot of the turrets and enemy ships before your last 'invasion' squad arrives.
TF2 and TF3 will cease fire upon the planet if all weapon platforms are destroyed (fleet strategy). This allows for a safe landing.

ofcourse... if the world is heavily defended then there may still be casualties.

Make sure your troop ships are heavily armored and stuffed with PD. Losing those ships is annoying, to say the least.

~Myrath

Another thing is that you can set the fleet's orders to stop firing at the planet when all weapons are destroyed. This setting does seem to work. they'll fire until all planetary weapons are out of commision. This may not actually include destroying them completely. But combined with a troop assault it usually works.

I've always found that if my fleet contaibns a task force with 'Capture Planet' then my ships ignore the planet completely and I lose a ton of ships to Weapons Platforms before my ground troops land and the fleet scarpers. Then I have to wait force my troops to conquer the world before returning.

Did you customize the "capture planet" order? I've found the defaults to be somewhat less than useful.

This doesn't answer your questions, but I don't think anybody's mentioned the rationale for the strategy's behavior, which is that most weapons will damage facilities and population in addition to weapons platforms. Fledgling colonies will frequently lose all their population before the weapons platforms are killed, which is a lousy outcome. But you should be able to configure some kind of middle ground. =/

I could be mistaken. But I was under the impression that with capture planet all ships assault the planet, until the defenses are gone.
The troops ship will drop it's troops as soon as it can.

~Myrath

For planet capture, I have seen what others say...
Transport charges forward to it's doom, and the war ships hold back...
I use 1 cruiser hull for troops with lots of shields and armor, and 1 cruiser with heavy PD for escort... A second escort if needed...
I charge the escorts to the range of planet defences, and charge the transport in to drop troops then turn and retreat.
If the transport ship starts taking hits, I move one of the escorts in which usually become the target and allow the transport ship to get out of range...Baseships work kinda well but when they are within the planets defence range, the planet weapons hit before the ship defences fire... and they are slow and sluggish...
Need fast ships for capture...

Just my .000000002 MegaCredits worth...

You are mistaken. If there is a troop transport with troops and the capture planet strategy present, no ship will fire on the planet disregarding whatever they have as strategy. You cannot change that.

If you want to destroy the weapon platforms you need two attacks: first a fleet without troop transports and with the strategy settings for a planet with colony "fire until all weapons gone". After this attack is done, you attack with a second fleet that has troop transporters and the capture planet strategy.

This is why I customize the strategies.....

I put the warships on "optimal firing range" and modify that to have them stop firing when they disable all the WPs.

I have in a seperate taskforce the transports and they have orders to capture it.

Sorry, but this does not work.
The ships in the task force with "optimal firing range" strategy will not fire on the planet. They will however attack ships, bases, satellites, fighters.
The troop transports will go to the planet immediately and (try to) drop the troops, even if there are still weapon platforms intact.

Manualy control the ships....

Won't work on PBW...

Any attempt to capture a heavily defended planet is a long-term battle. The first few waves will require heavy losses to the back-and-forth of defenses ringing the planet, including ships, satellites, mines, drones, carriers, and so forth. Then, when the planet is open to attack, you can send an attacking transport.

One way to do this is (thinking out of the box) use a battleship, cruiser or destroyer with massive assault cannons to take out planet orbital and ground defenses; and include onboard this initial attacking task force enough cargo holds to haul an impressive initial ground assault force. In the tutorial, ground forces cease destroying WP when the planet's "live" forces are defeated. The planet is then yours to re-colonize.

or you could just glass the planet and claim it with a colony ship. then use the transport to drop troops and WPs on the planet to prevent an easy re-capture. Use SpaceYard ships to build a few Space yard bases in orbit to quick start production while the planet builds up..

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Without ammo, nice guns are just sophisticated clubs.

I agree, capture first...
But if the defences are too tough, send in waves of fighters to thake out the defences, closely watching the planet, and pull out when the planets defenced are crippled, then drop troops...
PBM... send in fighters first...

Suicidal drones works well in my experience against planets.. they are so fast, i only lose a few to defenses before contact.
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Without ammo, nice guns are just sophisticated clubs.

Set your tranpsorts to "core" and then some attack ship as "escort" to draw fire. If I remember correctly the escorts will fire on the planet. After the troops are dropped it doesn't matter about the WP's because the troops will take them out.

You can also set some ships to picket and they will help "soften up" the planet.

Put your pd's on your escorts and heavy armor/shields on your troop carrier.

~Slimbo

Everything that has transpired has done so according to my design...

When you build your fleet, change the formation to something more useful (shield). Then set the default from Break formation=FALSE.

Place your troop transport in the center (usually as Leader or Task force leader) set the others as pickets and escorts.

The fleet will remain in formation (vulnerable troop transport surrounded by other ships) for the attack.