Background: Human space exploration is dangerous at all levels. Analog missions are field tests in locations that have physical similarities to extreme space environments. Based on the habitat location and procedures involved, the analog space mission can be divided into two groups: environmental and mission analogs. Research habitats, where analog space missions are conducted are usually located in Isolated, Confined, and Extreme environments such as deserts, polar regions, lava fields, bunkers, and underwater. The underwater analog space missions are considered high-fidelity environmental spaceflight analog. Currently, there are 3 underwater research analog habitats operational worldwide, two located in the ocean and one located in sweet water, the Deep Lab03. Material: The DeepLab 03 is a mobile underwater habitat with an inner volume of 20m3 located in Czechia. One analog space mission was conducted in the Deep Lab03 in 2021 and the other is planned for 08/2022. Three analog astronauts-aquanauts participated in these missions and spent 2 and 7 days underwater at the app. 7m depth. Various psychological and physiological experiments were carried out. Results: The initial findings from the conducted experiments and missions indicate, that the Deep Lab03 research underwater habitat is a unique high-fidelity environmental spaceflight analog.