DARPA has asked the aerospace industry to design a small, first-stage rocket that can launch into space, deploy another stage with 3,000 to 5,000 pounds of payload attached, then return to land on a runway and be ready to do it all over again the next day—ten days in a row. That’s much more often than any of the bigger rockets launch, none of which have actually achieved reusability yet. XS-1, as DARPA calls the experimental vehicle, won’t have time for extensive refurbishment. It should essentially be able to refuel and re-fly, like an airplane. And it should do it for $5 million per flight, around a tenth of the cost of a current launch
DARPA is putting up $146 million for Phase II of the project—building and flying an actual demonstrator
In 2014 for phase I, three teams were selected to do advanced design work on the XS-1: Boeing/Blue Origin, Northrop Grumman/Virgin Galactic/Scaled Composites, and XCOR/Masten were all funded to develop their concepts.
Boeing's concept for DARPA's XS-1 spaceplane. (Boeing)
SOURCE -DARPA ,Air and space magazine, boeing