• 
  Emily Calandrelli

   Herself - Host (41 episodes, 2014-2016)
• 
  Bernard A. Harris Jr.

  Self - Former Astronaut
• 
  Story Musgrave

  Self - Former Astronaut
• 
  Don Pettit

  Self - Astronaut
• 
  Lika Guhathakurta

  Self - Program Director, Dreamchaser
• 
  Derrick Pitts

  Self - Chief Astronomer, The Franklin Institute
• 
  James Oberg

  Self - Space Journalist and Historian
• 
  James R. Hansen

  Self - Author, First Man: The Life of Neil A. Armstrong

• 
  Andrew Aldrin

  Self - Buzz Aldrin's Son
• 
  Deborah Bass

  Self - NASA Mars Scientist
• 
  Matthew Golombek

  Self - NASA Mars Project Scientist
• 
  Chris McKay

  Self - NASA Senior Scientist
• 
  Teresa Segura

  Self - Scientist
• 
  Richard Zurek

  Self - NASA Chief Scientist - Mars Program
• 
  Joseph M. Acaba

  Self - Astronaut

• 
  Tiffany Miller Alexander

  Self - Lead Quality Engineer, Kennedy Space Center
• 
  Robert Zubrin

  Self - Author, The Case For Mars
• 
  Marc D. Rayman

  Chief Engineer, Dawn Mission, JPL
• 
  Geoffrey Notkin

  Self - President, Aerolite Meteorites Inc
• 
  Jeffrey Hoffman

  Astronautics Prefessor, MIT