The XS-1 program was announced in September 2013. It is complimentary of a related DARPA project, the ALASA (Airborne Launch Assist Space Access). Design contracts were to be awarded around May 2014 with the aim of flight in 2017 and orbit in 2018. Jess Sponable, the XS-1 program manager, spoke February 5 at NASA's Future In-Space Operations group stating "The vision here is to break the cycle of escalating space system costs, enable routine space access and hypersonic vehicles," and "The XS-1 program represents a return to the bold aerospace projects of decades past, when engineers from various government agencies came together to push the spaceflight envelope.
Unlike other DARPA programs that are handed off to parts of the United States military once proven successful, this effort is a partnership between the agency and industry. It is aimed at enabling lower-cost and more responsive launches of U.S. government satellites, and to recapture the commercial launch market lost to foreign competitors. The space plane must carry a 3,000–5,000 lb (1,400–2,300 kg) payload to low Earth orbit for less than $5 million per flight at a rate of 10 or more flights per year; currently, launching that type of payload requires using an Orbital Sciences Corporation Minotaur IV expendable booster, costing $55 million at a flight rate of around once a year. The XS-1 follows several previous failed attempts to develop a reusable space launch vehicle. The X-30 in the 1980s and X-33 VentureStar in the 1990s never flew due to immature technologies. DARPA's last attempt was the Responsive Access, Small Cargo, Affordable Launch (RASCAL) program in the early 2000s with the goal of placing 300 lb (140 kg) payloads in orbit for less than $750,000. It involved an SR-71 Blackbird with modified high-Mach, high-altitude turbojets and set for demonstrations in 2006, but the program was cancelled in 2005. DARPA believes the XS-1 is more feasible due to advanced technologies including light and low-cost composite airframe and tank structures, durable thermal protection, reusable and affordable propulsion, and aircraft-like health management systems.

The goals of the program as of September 2013 were:

  • hypersonic flight to Mach 10 (12,250 km/h) or higher
  • fast one-day turnaround time, including flying 10 times in 10 days
  • a 1,800 kilograms (4,000 lb) payload on a trajectory to orbit
  • launch cost less than 1/10 that of current launch systems, approximately US$5 million per flight
  • unmanned vehicle
  • utilize a reusable booster coupled with an expendable upper stage

On July 14th 2014, in a statement DARPA said Phase 1 design contracts had been awarded to three companies to develop a demonstration vehicle. The selected teamed companies are Boeing with Blue Origin, Masten Space Systems with XCOR Aerospace, and Northrop Grumman with Virgin Galactic. DARPA's spaceplane program manager Jess Sponable said "We chose performers who could prudently integrate existing and up-and-coming technologies and operations, while making XS-1 as reliable, easy-to-use and cost-effective as possible," and "We're eager to see how their initial designs envision making spaceflight commonplace - - with all the potential military, civilian and commercial benefits that capability would provide." Phase 2 of the project is projected to take place in 2015.

Northrop Grumman will use its aircraft, spacecraft, and autonomous systems experience to work with its team consisting of Scaled Composites to lead fabrication and assembly, and Virgin Galactic to head commercial spaceplane operations and transition; Virgin Galactic worked on the SpaceShip Two, the world's only commercial spaceline. The team also plans to leverage technologies developed during related projects for DARPA, NASA, and the U.S. Air Force Research Laboratory to give the government "return on those investments." Aircraft-like operations will be emphasized including a clean pad launch using a transporter erector launcher with minimal infrastructure and ground crews, highly autonomous flight operations, and horizontal landing and recovery on standard runways.

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