SAN DIEGO — The U.S. Defense Advanced Research Projects Agency (DARPA) is about to start a program to develop a reusable first stage that could be used to launch medium-sized satellites for as little as $5 million each.

Speaking Sept. 12 at the AIAA Space 2013 conference in San Diego, Pam Melroy, deputy director of DARPA’s Tactical Technology Office, said the agency would release a Broad Agency Announcement in the next few weeks for a program called Experimental Spaceplane, or XS-1. An industry day for the program is planned for early October.

“The goal of the program is to fly 10 times in 10 days, and to achieve Mach 10,” Melroy said. The XS-1 itself would not fly into orbit, but could carry an expendable upper stage to place payloads weighing up to 1,800 kilograms into orbit at a target price of $5 million per launch. The vehicle could also be used as a platform for hypersonics research.

Melroy’s presentation included several illustrations of potential XS-1 designs, all featuring wings. However, she said DARPA was not restricting the XS-1 program to winged designs. “The key is that it needs to be a reusable first stage,” she said.

DARPA plans to pursue XS-1 in parallel with the existing Airborne Launch Assist Space Access (ALASA) program, which is developing an air launch system designed to launch satellites weighing up to 45 kilograms for $1 million each. DARPA awarded ALASA system concept studies contracts last year to Boeing, Lockheed Martin and Virgin Galactic, and technology development contracts to three other companies. Melroy said some technologies developed for ALASA could be folded into the XS-1.

The XS-1 program is also similar to the Reusable Booster System (RBS), an Air Force Research Laboratory (AFRL) program to develop a flyback reusable first stage. AFRL terminated funding for the RBS Pathfinder program last year. Neil McCasland, former commander of AFRL, said at the conference that the Air Force had long recognized the potential benefits of reusable launch vehicles. “We deliberately thought through whether we would continue to invest in this, and the answer is no, because the horizon seemed too far off for the Air Force to consider,” he said.