1. National Aeronautics and Space Administration [NASA], FY 2017 budget
estimate (2017) [Internet], viewed 2021 Feb 17, available from: http://nasa.gov/sites/default/files/atoms/files/fy_2017_budget_estimates.pdf
2. European Space Agency, ESA budget 2017 (2017) [Internet], viewed
3. 2021 Feb 27, available from: http://esa.int/ESA_Multimedia/images/2017/01/ESA/_budget_2017
4. Japan Aerospace Exploration Agency, Evaluation of FY 2017 Operating
Results for JAXA (2018) [Internet], viewed 2021 Feb 17, available from:
http://mext.go.jp/component/b_menu/shingi/toushin/_icsfiles/afieldfile/2019/01/17/1412601_06.pdf
5. International Space Exploration Coordination Group [ISECG], Global
exploration roadmap, supplement: Lunar surface exploration scenario update
(2020) [Internet], viewed 2021 Aug 8 2020 Oct 23, available from: http://globalspaceexploration.org/wp-content/uploads/2020/08/GER_2020_supplement.pdf