Tracy Thumm, left, and Justin Kugler both from the International Space Station Program Science Office at Johnson Space Center speak at the STS-135 Tweetup, Thursday, July 7, 2011, at Kennedy Space Center in Cape Canaveral, Fla. About 150 NASA Twitter followers attended the event. The STS-135 mission will be NASA's last space shuttle launch. Photo Credit: (NASA/Paul E. Alers)

A Nasdaq moderator, center, talks with NanoRacks CEO Jeff Manber, left, NASA Manager of the International Space Station Research Office Marybeth Edeen, AlphaSpace Founder and Chairman Stephanie Murphy, and Made in Space Vice President of Advanced Programs and Concepts Justin Kugler, right, during a live social media event shortly after NASA announced a five-part plan to open the International Space Station to expanded commercial and marketing activities and private astronaut missions to the station and enable additional commercial destinations in low-Earth orbit, Friday, June 7, 2019 at the Nasdaq MarketSite in New York City. NASA will continue to maintain human presence and research in low-Earth orbit, and the long-term goal is to achieve a robust economy from which NASA can purchase services at a lower cost. Photo Credit: (NASA/Bill Ingalls)