Each Lander and Outpost has a limited supply of life support, which is consumed for all activities that require leaving the outpost/rocket. There is no penalty for running out of life support, except that most actions are then unavailable.
You can buy compressed Life Support Packs in the Market for 5 credits; each one, when unpacked, provides 5 points of life support to either a lander or outpost. Outposts can also generate life support at the Hydroponics building, slowly but continuously; with sufficient assigned workers and upgrades, this typically becomes your main source, since it is has no ongoing shipping costs. Life support created at the Hydroponics can be transferred to a ship at the Landing Pad, but it cannot be transferred in the other direction, from ship to outpost.
New landers start with full life support as part of their purchase price. Reusable landers automatically replenish their life support for free upon visiting Earth.