Season 1 Smithsonian Channel , 2013 - 2014 Season 2 Smithsonian Channel , 2014 - 2015 Season 3 Smithsonian Channel , 2016 Season 4 Smithsonian Channel , 2017 Season 5 Smithsonian Channel , 2018 Season 6 Smithsonian Channel , 2019 Season 7 Smithsonian Channel , 2021