The rocket engines are arranged in a ring around the major diameter of a SSTO.
The hydrogen tanks form what is , in effect, a a large plug, with a toroidal oxygen tank mounted forward.. The rockets are enclosed in an air duct equipped with adjustable inlets. A jettisonable shroud extends the mixing area down stream of the rockets. The conical payload fairing serves as an inlet spike during accent through the atmosphere. The air enter through the inlet, mixes with the rocket exhaust, is heated and expands past the plug-shaped aft body, thus contributing additional thrust. The mixing shroud is jettisoned and the inlets are closed after leaving the atmosphere