Putting monsters into orbit??!

[A_name]

Instead of seperatrons, use fins at the top of the stages angled 5* from vertical, outwards. The lateral lift will pull the stages away from the rest of the ship.

Won't this make the rocket want to flip?

[Superfluous J]

Won't this make the rocket want to flip?

Not if it's sufficiently top heavy. Fins help, but center of mass rules the day when it comes to stability.

[cephalo]

The critical thing on an unwieldy craft is to stay prograde (Possibly straight vertical) as long as possible. Don't touch any control until you're out of the thicker part of the atmosphere. Depending on your speed, even a small angle away from prograde can slap that nose aside and expose every atmospheric problem in your ship design at once.

[A_name]

Not if it's sufficiently top heavy. Fins help, but center of mass rules the day when it comes to stability.

Good to know, thanks.

[GeneralVeers]

Just how does one get a 90+ tonne vehicle into LKO and beyond? I mean, I've managed to get a few 80-90 tonne payloads in previous versions, but since they are so large, the rocket tends to be extremely unstable

Depends on what's making the rocket unstable.

With my first really large spacecraft (an interplanetary carrier that weighed two hundred tons!), it was weak joints. The launch vehicle tended to bend at the separators joining stages, moving the thrust vector off-center--usually too far for fins, SAS wheels, or gimballed thrusters to correct. The solution to this problem is multiple joints.

Or, is it aerodynamic effects? Is your ship one of those that flips around and stabilizes backwards on the way up? Then flips 180 again when it's heading back down and preparing to lithobrake? Anything that's aerodynamically unstable will become stable when it flips a 180--so launch it upside down. I tried this with my most recent lander model (my game save is called the Galactic Empire and this lander looks the part!), and it worked perfectly. The launch was rock-steady.

If your payload is big and clunky and doesn't lend itself easily to being launched upside down, try this: in the VAB, go to Structural parts, grab a modular girder segment, and put it up against the hull of the ship. Then hit any single WASD key twice, and note how the girder turns around so it's INSIDE your ship. When you place it, the exterior end of the girder will become an attachment point you can stick a decoupler on. That way you can attach several decouplers to the hull of the payload anywhere it's convenient, and build the launch vehicle from there.

[Wolfox]

Just how does one get a 90+ tonne vehicle into LKO and beyond? I mean, I've managed to get a few 80-90 tonne payloads in previous versions, but since they are so large, the rocket tends to be extremely unstable and requires something with a lower profile. (i.e: asparagus staging) I use the asparagus approach... but it's almost impossible to push away any of the stages from the central kerbodyne tank without the use of seperatrons, but they heat up the central rocket and cause it to explode. If I don't use seperatrons, the shed tanks just crash into it, and the push-away wing approach isn't sufficiently strong enough to push away such heavy spent tanks.

What methods are people using to get these monsters into orbit? I can't seem to go beyond 70 tonnes before I start running into launch stage design complications.

I sometimes use airbrakes for that purpose. Place them them as low as possible, radially on the opposite side than the main rocket, below the control fins, and start opening them (action group) just before fuel is depleted and you ditch them off.

This way:

a) Boosters are immediately after separation tilted away from main rocket.

Booster start to slow down by the air friction, taking them safely away from main rocket without extra help.

c) No extra heat is produced. Less rocket fuel means also less risky situations, unevenly placed sepatrons may cause wild Booster-dancing upon ditching.

I do not recommend using them instead of control fins, even though they can be used for steering, the do it via lot of drag, which slow down the rocked and badly impair its Delta-v needed for ascent.

The only downside is that airbrakes are little bit more costly than sepatrons.

Edited August 3, 2015 by Wolfox

[GoSlash27]

I sidestep the problem by simply not launching really big payloads.

I launch my monsters empty and/ or in sections, then assemble/ fuel/ crew them in LKO.

Best,

-Slashy

[Weywot8]

Regarding the booster-collision problem:

I've never had any problems with laterally-mounted boosters (e.g. asparagus tanks) colliding with the central rocket. The main thing is to make sure that you attach the booster as low as possible on the radial decoupler (i.e. the radial decoupler's attachment point on the radial tank is as high above the radial tank's CoM as possible).

Just to add to this, use the offset tool and push down the booster - the top of the booster should be attached to the radial decoupler. Also, use the "strutty" radial decoupler for more clearance if required. The placement should already prevent most collisions as the bulk of the booster is already "past" the main craft. The decoupler force also directs all the tanks outwards.

The booster tanks may occasionally crash into each other after decoupling. If that's a problem (i.e. using Stage Recovery to salvage parts for cash), add a parachute at the centre of mass of the booster tansk, staged to open at the same time the booster is decoupled. Even if the chute gets destroyed, it's still "recovered" in the end.

[Sharpy]

I used a bit different approach with the separatrons. So they heat the central tank and it explodes? Nope. I aimed them right into the radial tanks. No decouplers at all, simply separatrons right into the tanks.