I figured I might as well post one of my designs that just happened while I was testing 1.2 early access (so no mods required). I wanted to build a rather huge spaceplane that can bring a station up in orbit... but of course that was not big enough! First I tried making several streches of mk3 bays but I could not quite get those designs go fast enough to make it into orbit.
The result was one long mk3 bay for the main station parts and two bays for solar cell arrays etc. additional bits and pieces.
~45 tons of payload to LKO
173 parts, 195 tons of weight with no cargo, 353k funds.
A pic is more telling than many words, so here she is looking all pretty in orbit (gotta have moar lights!):
Here are craft files if you want to try it out:
Craft file for just the plane
Same craft with the test load station bits visible on the screenshot above.
The plane is not really fully optimized but it's already fairly easy to fly (well after some tries..). I like to set SAS on and caps lock the fine controls on.
Stage to set off with the air breathing engines, there is not very much pitch authority but she is steady on the runway so I like to keep her straight until the end of the runway and then pitch up when the runway falls off. Try to keep building speed all the time to get the engines to the powerband, then start pitching up more, still maintaining some acceleration. I like to keep one rapier and one whiplash detail window open to follow the thrust, first point about 5 degrees pitch to build speed, once you see thrust build up fast pitch up a couple of degrees more, still maintaining acceleration and increasing thrust. Once the rapiers go well past 300 kN you should be able to start pitching up carefully. When the air-breating mode runs out of steam it's time to stage the poodle in (ISP is already good) and switch the rapiers to closed cycle. Once your time to Ap starts rising fast it's time to shut off the rapiers and let the poodle take you to orbit slowly, around 10 degrees pitch prograde will be sufficient to maintain the climb and build speed.
Action groups are needed to control the engines: Hit 1 to switch the rapiers to closed cycle mode when you start losing so much thrust that you don't gain any more speed. Hit 2 when the whiplashes run out of power (closes also the intakes). hit 4 to toggle the rapiers off to use just the poodle for finalizing orbit / orbital maneuvres. 3 controls the cargo bay doors.
I haven't really tweaked everything to be optimal, I'm sure this can be still improved fairly easily to get better performance and maybe cut some costs. The RCS may not be perfect since RCS balancer was not working with 1.2 when I built this, etc.
The amount of liquid fuel / ox you need really depends on the ascent profile and payload.. experiment!
A gradual descent deorbit should work, the huge hull means you can do effective aerobraking and lose some speed in the upper atmo, but avoid large pitch AOA in the atmosphere, if you flip it is game over..