In stock you can make a working SSTO with one RAPIER engine, a fuel tank, monoprop tank, some intakes and a rocket capsule. Last time I flew this configuration I would get to altitude with about 5% fuel remaining, do circularization, station rendezvous, and deorbiting with monoprop, and then land tail-down on that last sip of fuel.
In stock you can make a working SSTO with one RAPIER engine, a fuel tank, monoprop tank, some intakes and a rocket capsule. Last time I flew this configuration I would get to altitude with about 5% fuel remaining, do circularization, station rendezvous, and deorbiting with monoprop, and then land tail-down on that last sip of fuel.