•
Joel Kinnaman as Edward "Ed" Baldwin (seasons 1–5), one of NASA's top astronauts, initially based on
Apollo 10 commander
Thomas P. Stafford •
Michael Dorman as Gordon "Gordo" Stevens (seasons 1–2; guest season 5), an astronaut and Ed's best friend, based on
Apollo 10's lunar module pilot
Gene Cernan an astronaut and member of "Nixon's Women" who later becomes
Administrator of NASA, a United States senator and President of the United States following the
1992 presidential election •
Wrenn Schmidt as Margo Madison, a NASA engineer who was mentored by
Wernher von Braun, inspired by
Margaret Hamilton •
Sonya Walger as Molly Cobb (seasons 2–3; recurring season 1), an astronaut and member of "Nixon's Women", based on
Jerrie Cobb •
Krys Marshall as Danielle Poole (seasons 2–4; recurring season 1; guest season 5), an astronaut and member of "Nixon's Women" •
Cynthy Wu as Kelly Baldwin (née Hanh Nguyen, before adoption) (season 2–present), a scientist and Ed and Karen's adopted daughter • Casey W. Johnson as Danny Stevens (seasons 2–3; guest season 4), an astronaut and Gordo and Tracy's son • Jason David and
Mason Thames as young Danny Stevens (recurring season 1) •
Coral Peña as Aleida Rosales (season 2–present), an
illegal immigrant who is fascinated by space and later gets mentored by Margo • Olivia Trujillo as young Aleida Rosales (recurring season 1) •
Edi Gathegi as Dev Ayesa (season 3–present), the founder of Helios Aerospace, a private space company with the goal to reach
Mars before NASA and the Soviet Union •
Toby Kebbell as Miles Dale (season 4–present), a former offshore
oil platform worker who pursues a new job opportunity on Mars •
Tyner Rushing as Samantha Massey (season 4), a space worker on the Mars colony •
Svetlana Efremova as Irina Morozova (season 4; guest season 5), a high-ranking Soviet official •
Daniel Stern as Eli Hobson (season 4), the NASA administrator •
Mireille Enos as Celia Boyd (season 5), a member of the Peacekeeper Security Force on Mars •
Costa Ronin as Leonid "Lenya" Polivanov (season 5), a Soviet politician and former cosmonaut, and governor of Mars •
Sean Kaufman as Alex Poletov Baldwin (season 5), son of Kelly Baldwin and Ed's grandson • Ezrah Lin as young Alex Poletov (recurring season 4) •
Ruby Cruz as Lily Dale (season 5), the youngest daughter of Miles and Amanda Dale • Piper Rubio as young Lily Dale (recurring season 4) • Ines Asserson as Avery "A.J." Jarrett (née Stevens) (season 5), a U.S. Marine training for a space mission and the daughter of Danny and Amber Stevens • Delaney Claire Evans and Parker Reese Evans as an infant Avery Stevens (guest season 3) • Ellie Grace Pomeroy as a young Avery Stevens (guest season 4) ==Episodes==