With only hours to go before Atlas' planned touchdown on Mars, Emma is confronted with everything that could go wrong, while Lu receives new orders.

Emotions run high as rapidly dwindling water rations on the Atlas leave the crew and Mission Control scrambling to find a fix before time runs out.

A problem with Atlas' supply ship jeopardizes the mission and sparks questions about Emma's commitment to landing on Mars.

Emma's behavior becomes a cause for concern, Kwesi and Lu team up on a plant mystery, and Lex makes an impulsive decision with far-reaching consequences.

Tempers flare on the Atlas over a water-system glitch and an act of betrayal. As Matt works on the ship's issue, he accidentally meets Lex's new friend.

As Christmas approaches, the crew prepares to make their final calls home before communication grows spotty. Matt and Lex adjust to their new normal.

Emma puts herself in harm's way when Ram unwittingly endangers the lives of everyone on the Atlas. Matt must make a wrenching decision about his future.

A staff change at Mission Control upsets the usually unflappable Lu, and the fallout undermines Emma's command. Matt encourages Lex to return to school.

When a ship malfunction threatens the voyage before it's barely begun, Emma works with a wary Misha on a high-risk repair operation.

As the mission launches, Emma finds her mettle as commander tested by an onboard accident, a divided crew and a family emergency back on Earth.