Whitesides, Loretta Hidalgo (July 9, 2008). “Why NASA Isn’t Trying to Human-Rate the Atlas V or Delta IV Rockets”. Wired. 2018年3月29日閲覧。 “"You could launch a smaller human vehicle on a current expendable rocket [...] In fact, before the Columbia disaster NASA teams were working on an Orbital Space Plane (OSP) designed to do just that."”