The microbiome of inhabited space stations mainly consists of human-associated microorganisms, which inevitably accompany astronauts on their missions into space as a natural part of the human body. However, these microorganisms pose challenges for space travel and the success of space missions. Astronauts experience physiological changes as well as impaired immune function during spaceflight which could increase the risk of infectious diseases on long term missions. Additionally, changes in microbial physiology and gene expression have been observed and it is still being discussed if this affects astronaut health. Microorganisms can threaten spacecraft integrity, particularly through the formation of biofilms that can cause corrosion and biofouling. The search for extraterrestrial life is a primary goal of future astrobiological missions. To prevent false positives, microbial forward contamination of other celestial bodies such as Mars has to be prevented. To address these different aspects of space microbiology research, this thesis used the human-associated bacterium Staphylococcus capitis subsp. capitis as model organism, specifically S. capitis subsp. capitis strain K1 (DSM 111179) that was previously isolated from the International Space Station (ISS). Strain K1 was included in a stratospheric balloon flight (MARSBOx) that simulated Mars surface conditions to investigate if S. capitis could survive on Mars and compromise the success of astrobiology driven missions. To test if copper-containing antimicrobial surfaces can prevent biofilm formation of S. capitis in reduced gravity conditions, K1 was included in an experiment onboard the ISS (BIOFILMS). Additionally, K1 was phenotypically characterized, its genome sequenced and compared to three other S. capitis subsp capitis strains, including the type strain (DSM 20326^T ), to determine if the ISS isolated strain K1 showed any health-relevant alterations. The results of the MARSBOx experiment showed that S. capitis is unlikely to survive for an extended period on the surface of Mars. This is mainly due to its sensitivity to UV-C radiation, which was found to be within the same range for all four strains. Moreover, all tested strains were tolerant to desiccation, and in MARSBOx, K1 survived desiccation for five months in a simulated Martian atmosphere. All strains exhibited better survival in an anoxic atmosphere, which is likely due to lower generation of reactive oxygen species (ROS). Preliminary results of the BIOFILMS experiment showed that reduced gravity did not influence the antimicrobial effectiveness of copper against S. capitis. No apparent difference in attached and damaged cells was detected between microgravity and 1 x g samples. In additional experiments, it was observed that biofilm formation of strain K1 is highly influenced by the surface to which the cells adhere and the overall cultivation conditions. The further comparison of the ISS isolated S. capitis subsp. capitis strain K1 with the other three strains showed that K1 exhibited increased growth and a higher weighted average melting temperature of fatty acids (~3 °C) but did not show any significant changes in virulence, metabolism, antibiotic susceptibility, radiation or desiccation tolerance. The type strain was found to be degenerated compared to the other strains as it showed slow growth and low tolerance to desiccation. S. capitis subsp. capitis strain D3 (DSM 31028) showed the highest desiccation tolerance and biofilm formation, presumably due to selection pressure in its location of isolation: a clean room of a spacecraft assembly facility. S. capitis subsp. capitis H17 (DSM 113836) and strain K1 showed delayed yellow colony pigmentation, which was increased under low nutrient conditions and longer incubation periods. Tentative identification of the pigmentation revealed staphyloxanthin and derivates. The two pigmented strains exhibited increased tolerance to H₂O₂ and long-term storage at -20 °C but no difference in ROS scavenging activity of the methanol cell extracts was detected. In conclusion, although S. capitis subsp. capitis strain K1 did not survive prolonged exposure to full space conditions, human-associated bacteria are still relevant to consider for planetary protection, spacecraft integrity and astronaut health. Even if no health-relevant changes occurred in the ISS-isolated strain, further research on bacterial adaptation to space conditions is necessary. The application of antimicrobial surfaces, such as copper-containing surfaces, could be a potential strategy to reduce bacterial contamination and biofilm formation in specific areas of a space station.