This is probably beyond the charter of this group but . . . .
The Reaction Engines precooled engine may be the most advanced in the
world. It gets good performance up to 26 km on air before it switches
to internal LOX for the last 6 km/s to orbit.
The really sticky part is the precooler, but Reaction Engines has
installed a huge capacity to make them and just might be willing to
supply some.
The only thing more impressive than a SSTO would be an amateur SSTO.
Worth discussing? Or is it just too far over the horizon?
Keith