Re: A successor to the STS with Atlas 5 ?
The HL-20, on which the Dream Chaser was modeled, was intended to use escape rockets and parachutes for launch pad abort. I expect a similar concept will be developed for Dream Chaser, probably using its own rockets in an escape mode.
The HL-20 was intended in part as a Space Station rescue vehicle, and the advantages over a capsule include a more benign reentry environment (lower g's) for possibly injured astronauts, and a broader choice of landing sites.