You buggers have had me up until nearly 2am again trying to get an SSTO space plane going (single stage to orbit). These things are tricky. On my little space planes (10-12t) less than 10% mass change can make the difference between winning and losing. I've had such a time of it.This design, too big and floppy. Also, didn't make it to orbit.This design? Not enough rocket fuel.And then itterate on that a half dozen times until we get to the Bumbebee IV, the perfect balance between engine, lift, weight, rocket fuel load, etc etc. Comes in at 11.5t. Reaches 1,600m/s at about 28,000m before we turn on the motors. Climbs steadily at 60 degrees from just after take off.Only different from other, similar craft is two of those small poodle engines, a little less weight in RCS thrusters, two "ball" RCS tanks fewer and no struts. That's a half ton+ of savings right there.Whadoyaknow?Docks up nicely too!Tip: placing landing gear makes a WORLD of difference to planes, I find. You want to be reasonably close with the back ones to the line where your centre of gravity is or you won't be able to lever the nose up. If your wings are in any way angled, (eg, up, which they should be. A slight V when seen from the nose helps stability) then landing gear glued to angled things (as in, not parallel with the ground) will cause your craft to be very hard to drive around on the ground. Keep the landing gear stuck to fuel tanks and plane bodies and other things parallel to the ground. Also, angle your wings slightly up (as in their leading edge is higher than their trailing edge). The aerodynamics model in KSP is no more complex than this for generating lift.Phew. SSTO. What a challenge!