Okay, efficient single-stage-to-orbit is probably not possible without cheating. Here's a serious try at a real orbiter. Though it was not totally in vain, all that experimenting with number of tanks versus number of nozzles, found a sweet spot at two nozzles, 3-7 tanks. The first stage is sixteen stock solid motors and four SAS modules. Double and triple in-line couplers were used to build it. It tops out about 2800m and 160m/s. The second stage is nine solid motors and two SAS modules. It tops out about 7500m and 200m/s. It's H-shaped to let the tines of the third-stage fork pass through it. They can be fired simultaneously even, but that's less efficient. It takes some gimbal work to make it fly steady. The third stage is six fuel tanks, a three-way in-a-row coupler, one SAS module, microengine, miccrotank, and the control module. It accelerates from 200m/s to >2500m/s on those six tanks alone! It took trial and error to find a shape for all that which is still stable with one SAS module. [edit] I have successfully orbited in this craft now, and as such call it the Mark I Orbiter.