1. Space Foundation publication, The Space Report 2012. Available from: 〈www.spacefoundation.org/programs/research-and-analysis/space-report〉.
2. Wal-Mart Annual Report, Five-Year Financial Summary, 2012, p. 17 (19/62). Available from: 〈www.walmartstores.com/sites/annual-report/2012/WalMart_AR.pdf〉.
3. The Commercial Space Transportation Study, 1994. Available from: 〈www.hq.nasa.gov/webaccess/CommSpaceTrans〉.
4. NASA ASCENT Study Final Report, Futron Corporation 2003. Available from: 〈www.futron.com/pdf/resource_center/reports/ASCENTFinalReport_V1.pdf〉.
5. D.P. Rainer, J. Sponable, T. Fry, J. Zanzig, J.R. Ethier, M. Burnside-Clapp, A Rocket-Powered Technology Demonstrator for Responsive Access to Space, in: Proceedings of the AIAA-3rd Responsive Space Conference, AIAA-RS3 2005–6006, 2005.