NASA's outline for lunar exploration in the 2020s
NASA
<a rel="nofollow" class="external free" href="https://www.nasa.gov/sites/default/files/atoms/files/a_sustained_lunar_presence_nspc_report4220final.pdf">https://www.nasa.gov/sites/default/files/atoms/files/a_sustained_lunar_presence_nspc_report4220final.pdf</a>