The Reusable Booster System (RBS) was a United States Air Force research program, circa 2010 to 2012, to develop a new prototype vertical-takeoff, horizontal-landing (VTHL)[1] reusable booster and a new prototype expendable second stage to replace the existing Evolved Expendable Launch Vehicles (EELV) after 2025.
[1]"Officials anticipate awarding up to three contracts for the project, where winners would compete for individual tasks of experiments and demonstrations that address technology, processes and other attributes of a reusable booster system, or RBS."
[4] In December 2011, Lockheed Martin was awarded a contract to build a flight demonstration vehicle, the RBS Pathfinder, which was to have been completed in 2015.
[5] It was being developed under the Air Force Research Laboratory's (AFRL) RBS Flight and Ground Experiments (RBS-FGE) program.
[3] Among other factors, the October 2012 NRC report suggested that the Air Force "should develop and fly more than one Pathfinder test vehicle design [and that] competition amongst RBS concepts should be maintained as long as possible to obtain the best system for the next generation of space launch.