The major goal of the project is to reuse the spacecraft frequently, with a proposed launch rate of 10 missions in just 10 days.
DARPA's concept follows decades of reusability dreams by space advocates. The space shuttle is the most famous operational attempt at reusability, but that system could only be partially recycled. For example, new external tanks were manufactured for every mission, and a certain number of tiles on the re-entry protection system had to be replaced after each flight.
The XS-1 (Experimental Spaceplane 1) is envisioned to heft payloads for less than $5 million a flight, each weighing between 3,000 and 5,000 lbs. (1,360 to 2,267 kilograms). The aircraft-like craft is also supposed to fly faster than Mach 10, or 10 times the speed of sound.
"Technologies derived from the XS-1 program will enable routine space launch capabilities with aircraft-like cost, operability and reliability," read a DARPA announcement from November 2013 cited in a 2014 Space.com article.
"The long-term intent is for XS-1 technologies to be transitioned to support not only next-generation launch for government and commercial customers, but also global reach hypersonic and space access aircraft."