This is my source: http://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?no-ist=&page=2 http://www.airspacemag.com/space/is-spacex-

This is my source: http://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?no-ist=&page=2 http://www.airspacemag.com/space/is-spacex-changing-the-rock... It's four years old.