HSF Final Report: Seeking a Human Spaceflight Program Worthy of a Great NationArchived 2009-11-22 at the Wayback Machine, October 2009, Review of U.S. Human Spaceflight Plans Committee, p. 64-66: "5.2.1 The Need for Heavy Lift ... require a “super heavy-lift” launch vehicle ... range of 25 to 40 mt, setting a notional lower limit on the size of the super heavy-lift launch vehicle if refueling is available ... this strongly favors a minimum heavy-lift capacity of roughly 50 mt ..."
Kutter, Bernard; Monda, Eric; Wenner, Chauncey; Rhys, Noah (2015). Distributed Launch - Enabling Beyond LEO Missions(PDF). AIAA 2015. American Institute of Aeronautics and Astronautics. Retrieved 23 March 2018.
HSF Final Report: Seeking a Human Spaceflight Program Worthy of a Great NationArchived 2009-11-22 at the Wayback Machine, October 2009, Review of U.S. Human Spaceflight Plans Committee, p. 64-66: "5.2.1 The Need for Heavy Lift ... require a “super heavy-lift” launch vehicle ... range of 25 to 40 mt, setting a notional lower limit on the size of the super heavy-lift launch vehicle if refueling is available ... this strongly favors a minimum heavy-lift capacity of roughly 50 mt ..."