The XS-1 is a space plane under development by the U.S. military's high-tech agency, the Defense Advanced Research Projects Agency (DARPA). 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."
DARPA originally announced the program in 2013 and it is now in Phase 1. In 2014, three teams were selected to compete for the flight contract:
- Northrop Grumman leading the team, with Scaled Composites doing manufacture-assembly and Virgin Galactic doing operations
- Masten Space Systems (lead) and XCOM Aerospace
- Boeing (lead) and Blue Origin
“In an era of declining budgets and adversaries’ evolving capabilities, quick, affordable and routine access to space is increasingly critical for both national and economic security,” DARPA said in a 2014 press release.
DARPA pointed out that satellite launches on rockets must be scheduled years in advance and cost a lot of money. “DARPA created its Experimental Spaceplane (XS-1) program to help overcome these challenges and create a new paradigm for more routine, responsive and affordable space operations,” the agency added.
Tasks for Phase 1 include developing the vehicle, finding and reducing the risk of creating the “core” technologies and processes, and figuring out how to move forward into the flight phase, DARPA said.
“DARPA expects the performers to explore alternative technical approaches from the perspectives of feasibility, performance, system design and development cost and operational cost. They must also assess potential suitability for near-term transition opportunities to military, civil and commercial users,” the agency wrote.
Masten's released artist's concept in 2014 suggests that the system would take off and land vertically and would include a tail fin and wings, something that was not present on previous systems, according to a previous Space.com article.
Northrop's artist's concept depicts a plane that would be used from a simple launcher, one that wouldn't require much ground crew to service, according to a 2014 GizMag article. Boeing has also released an artist's concept showing the plane soaring on its way to space.
DARPA expects to narrow down the field of competitors to just one company in 2015, when it enters Phase 2 of the project. A test flight is expected in 2018, and in the future the program could be done by the Navy, the Air Force or a commercial operator.
Should it make it to flight, the XS-1 would soar to suborbital altitudes using the reusable first stage, DARPA added. The plane would then release a non-reusable upper stage to send a satellite into low Earth orbit. The spaceplane would return for a conventional landing and to prepare for another flight.
“Modular components, durable thermal protection systems and automatic launch, flight and recovery systems should significantly reduce logistical needs, enabling rapid turnaround between flights,” DARPA wrote.