The U.S. Defense Advanced Research Project Agency’s (Darpa) goal with its new Experimental Spaceplane (XS-1) program is to demonstrate a reusable capability that can transition to industry for low-cost military and commercial satellite launches and hypersonic technology testing.

The agency usually hands off successful programs to one of the U.S. military services, but “Darpa’s XS-1 transition partner is you — industry,” Program Manager Jess Sponable told attendees at a proposers’ day briefing earlier this month.

In addition to enabling lower-cost, more-responsive launches of U.S. government satellites, Darpa sees the reusable first-stage technology to be demonstrated under the XS-1 program as key to recapturing a commercial launch market lost to foreign competitors.

The program’s goal is to fly an X-plane reusable first-stage to demonstrate technology for an operational system capable of launching 3,000-5,000-lb. payloads to low Earth orbit for less than $5 million per flight at a launch rate of 10 or more flights a year.

This compares with around $55 million to launch that class of payload on the Orbital Sciences Minotaur IV expendable booster, which operates at a flight rate of around one a year, according to Darpa’s program presentation.

The agency plans to award three or four $3-4 million Phase 1 preliminary design contracts in the first quarter of 2014, followed a year later by a single design-to-cost contract worth up to $140 million to build and fly an X-plane demonstrator.

If the program proceeds into Phases 2 and 3, first flight is scheduled for the third quarter of 2017, leading to an orbit flight demonstration a year later.

The technical objectives are to fly the XS-1 10 times in 10 days; fly to Mach 10-plus at least once; and launch a demonstration payload into orbit.

The 10 flights in 10 days are intended to demonstrate reusability and expand the flight envelope. There is no velocity requirement for the flights, but the vehicle must take off and land each time.

Flying to Mach 10 or beyond will demonstrate that the XS-1 can reach a staging speed that minimizes the size of the expendable upper stage, for which a target cost of $1-2 million has been set.

There are no dynamic-pressure or load-factor requirements, but designing for Mach 10-plus will require the demonstrator to have the aero-thermal capability needed for space access and hypersonic testing.

Similarly there is no payload mass requirement for the launch to orbit, the objective being to demonstrate the potential for orbital flight in an operational version of the vehicle, Darpa says.

There are several configurations, propulsion systems and launch and recovery methods that could be proposed, the presentation says. But Darpa’s reference X-plane is an F-15-sized vertical-takeoff/horizontal-landing winged spaceplane powered by two SpaceX Merlin 1D rocket motors.

Gross liftoff weight for the reference vehicle is almost 224,000 lb., compared with 190,000 lb. for a Minotaur IV carrying a 4,000-lb. payload. The expendable upper stage would weigh 15,000 lb. including payload. The design could be scaled up using NK-33/AJ26 engines, air launch or two stages, Darpa says.

The stated objective of the XS-1 program is to “break the cycle of escalating space system costs,” the agency says, pointing out that GPS III will cost $500 million for the satellite and $300 million for the launch, compared with $43 million for the satellite and $55 million for the launch of the first GPS in 1978.

Previous attempts to develop a reusable launch vehicle have failed, the agency acknowledges, arguing that the early-1990s X-30 and late-1990s X-33 never flew because the technology was not available and the designs never closed.

Advances that should make the concept feasible this time around, Darpa believes, include lower-weight, lower-cost composite airframe and tank structures, durable thermal protection, available propulsion that is reusable and affordable, and health management systems that enable aircraft-like operations.