The program aims to achieve launches to low Earth orbit in days, compared to the months or years of preparation currently needed to get a single satellite into orbit. Success will depend upon significant advances in both technical capabilities and ground operations.
Jess Sponable, DARPA program manager, said: “The XS-1 would be neither a traditional airplane nor a conventional launch vehicle, but rather a combination of the two with the goal of lowering launch costs by a factor of ten and replacing today’s frustratingly long wait time with launch on demand.”
The XS-1 program envisions a fully reusable unmanned vehicle, roughly the size of a business jet, that would take off vertically like a rocket and fly to hypersonic speeds. The vehicle would be launched with no external boosters, powered solely by self-contained cryogenic propellants.
Upon reaching a high suborbital altitude, the spaceplane would release an expendable upper stage able to deploy a 1350kg satellite to polar orbit. The reusable first stage would then bank and return to Earth, landing horizontally like an aircraft, where it could be prepared for its next flight, potentially, within hours.
In its pursuit of aircraft-like operability, reliability, and cost-efficiency, DARPA and Boeing plan to conduct a flight test demonstration, flying 10 times in 10 days, with an additional final flight carrying the upper-stage payload delivery system. If successful, the program could help enable a commercial service in the future that could rival SpaceX, operating with recurring costs of $5 million or less per launch.
The XS-1 technology demonstrator’s propulsion system is an Aerojet Rocketdyne AR-22 engine, a version of the legacy Space Shuttle main engine (SSME). Other technologies include advanced lightweight composite cryogenic propellant tanks to hold liquid oxygen and liquid hydrogen propellants; hybrid composite-metallic wings and control surfaces able to withstand the physical and thermal stresses of hypersonic flight; and automated flight.
XS-1 Phase 2 includes design, construction, and testing of the technology demonstration vehicle through 2019. Phase 3 objectives include 12 to 15 flight tests, currently scheduled for 2020.
