http://www.stiintaonline.ro/propulsia-ionica-si-viitorul-explorarilor-spatiale/

https://ro.wikipedia.org/wiki/Descoperirea_%C8%99i_explorarea_sistemului_solar#cite_note-2

http://www-pao.ksc.nasa.gov/history/mercury/mr-3/mr-3.htm

http://www.descopera.org/primul-om-in-spatiu/

https://playtech.ro/2015/sputnik-1-satelitul-care-a-dat-startul-erei-spatiale/

http://www.istorie-pe-scurt.ro/laika-prima-calatoare-cosmica/

https://www.nasa.gov/exploration/whyweexplore/why_we_explore_main.html#.WIpIt33D9_k

http://www.aerospace.org/education/stem-outreach/space-primer/a-brief-history-of-space-exploration/