some previous systems have taken, using simple engine systems with "low-tech" fuels, as the Russian and Chinese space programs still do. An alternative to scale is to make the discarded stages practically reusable: this was the original design goal of the Space Shuttle phase B studies, and is currently pursued by the SpaceX reusable launch system development program with their Falcon 9, Falcon Heavy, and Starship, and Blue Origin using New Glenn. See also Aerospike engine Bristol Spaceplanes British Aerospace HOTOL Kankoh-maru Launch loop Lockheed Martin X-33 Mass fraction NASA X-43 Orbital ring Rockwell X-30 Roton Scramjet Space elevator Spacecraft propulsion Three-stage-to-orbit Two-stage-to-orbit VentureStar XS-1 (spacecraft) Further reading Andrew J. Butrica: Single Stage to Orbit - Politics, Space Technology, and the Quest for Reusable Rocketry. The Johns Hopkins University Press, Baltimore 2004, . References External links A Single-Stage-to-Orbit Thought Experiment Why are launch costs so high?, an analysis of space launch costs, with a section critiquing SSTO The Cold Equations Of Spaceflight A critique of SSTO by Jeffrey F. Bell. Burnout Velocity Vb of a Single 1-Stage Rocket Rocket propulsion Space access 1 Spacecraft propulsion