Watch Stowaway (2021) online

Stowaway is a 2021 science fiction thriller film, written by Joe Penna and Ryan Morrison and directed by Penna. The film stars Anna Kendrick, Daniel Dae Kim, Shamier Anderson, and Toni Collette. The film was released by Netflix and Prime Video (in Canada) on April 22, 2021.
The crew of MTS-42, a two-year mission to Mars, consists of commander Marina Barnett, biologist David Kim, and medical researcher Zoe Levenson. After taking off from Earth, the upper stage of their launch vehicle is connected by 450 metre long tethers to the ship's main hull, acting as a counterweight for inertia-based artificial gravity.

Shortly after takeoff, Barnett discovers launch support engineer Michael Adams, an accidental stowaway, unconscious behind a panel. The crew begins to bond with him, but Barnett soon learns that Michael's body had been entangled with, and inadvertently destroyed, a device which scrubs carbon dioxide from the air on the ship.

The crew are forced to use emergency lithium hydroxide canisters to scrub CO
2 from the air. However, the canisters can only sustain enough oxygen for two passengers. Barnett orders David to immediately cultivate his algae experiment on the ship, rather than at the Martian colony as planned. Only half of the algae survives, providing just enough oxygen for a third crew member. Without another oxygen supply, the crew of four will asphyxiate weeks before reaching Mars.

Barnett asks mission control for a solution that will save all four passengers, but the only option – an untested EVA to climb the tethers and recover liquid oxygen from the launch vehicle – is deemed too risky. Barnett and David come to terms with sacrificing Michael, but Zoe convinces them to wait ten days for mission control to think of another solution.

After three days, David explains the situation to Michael and offers him a painless lethal injection. Michael nearly takes his own life, but Zoe convinces him to hold out for a while longer. She insists on climbing the tethers to retrieve the liquid oxygen. David reveals that the rest of the algae has died, leaving only enough oxygen for two, and agrees to join her.

Zoe and David perform the EVA and fill two tanks, which would be enough to sustain two more passengers. However, deadly radiation from a high-energy solar flare forces them to leave one of the tanks behind. They make it back to the ship, but not before Zoe misses a step, which causes her to drop the tank, which drifts away. Meanwhile, the large tank is slowly leaking oxygen.

After regrouping, the crew realizes that one person must ignore the radiation and retrieve the tank left behind on the first attempt, so that the other three can survive. Marina must survive to pilot the ship, but the other three all volunteer to make the sacrifice. When Zoe ultimately insists on doing it herself, she manages to fill and return the tank to the ship before succumbing to radiation poisoning. She spends her final moments outside the ship, gazing at Mars amongst the stars.