Abstract
With long-term missions to Mars and beyond that would not allow resupply, a self-sustaining Bioregenerative Life Support System (BLSS) is essential. Algae are promising candidates for BLSS due to their completely edible biomass, fast growth rates and ease of handling. Extremophilic algae such as snow algae and halophilic algae may also be especially suited for a BLSS because of their ability to grow under extreme conditions. However, as indicated from over 50 prior space studies examining algal growth, little is known about the growth of algae at close to Mars-relevant pressures. Here, we explored the potential for five algae species to produce oxygen and food under low-pressure conditions relevant to Mars. These included Chloromonas brevispina, Kremastochrysopsis austriaca, Dunaliella salina, Chlorella vulgaris, and Spirulina plantensis. The cultures were grown in duplicate in a low-pressure growth chamber at 670 ± 20 mbar, 330 ± 20 mbar, 160 ± 20 mbar, and 80 ± 2.5 mbar pressures under continuous light exposure (62–70 μmol m–2 s–1). The atmosphere was evacuated and purged with CO2 after sampling each week. Growth experiments showed that D. salina, C. brevispina, and C. vulgaris were the best candidates to be used for BLSS at low pressure. The highest carrying capacities for each species under low pressure conditions were achieved by D. salina at 160 mbar (30.0 ± 4.6 × 105 cells/ml), followed by C. brevispina at 330 mbar (19.8 ± 0.9 × 105 cells/ml) and C. vulgaris at 160 mbar (13.0 ± 1.5 × 105 cells/ml). C. brevispina, D. salina, and C. vulgaris all also displayed substantial growth at the lowest tested pressure of 80 mbar reaching concentrations of 43.4 ± 2.5 × 104, 15.8 ± 1.3 × 104, and 57.1 ± 4.5 × 104 cells per ml, respectively. These results indicate that these species are promising candidates for the development of a Mars-based BLSS using low pressure (∼200–300 mbar) greenhouses and inflatable structures that have already been conceptualized and designed.
Highlights
Human exploration of Mars is one of the key scientific and technological undertakings of our time, providing critical information enabling the discovery and settlement of another world while facilitating the development of technologies on Earth
The statistical analysis on the optical density (OD) measurements at 670 mbar indicated that C. brevispina, C. vulgaris, K. austriaca, and D. salina showed statistically significant (p < 0.05) growth at 670 mbar, whereas S. plantensis did not show statistically significant growth (Figure 2 and Supplementary Table 9)
We chose the strains C. brevispina, D. salina, and C. vulgaris as candidate strains for further detailed quantitative growth analysis using cell counts at lower pressures (Supplementary Tables 1–3 and Figure 2)
Summary
Human exploration of Mars is one of the key scientific and technological undertakings of our time, providing critical information enabling the discovery and settlement of another world while facilitating the development of technologies on Earth. Current research and planning to send crewed missions to Mars for long term space exploration has underscored the critical need for advanced Bio-regenerative Life Support Systems (BLSS), which are complex mixtures of biological and engineering systems that include atmosphere revitalization, water recycling, food production, and organic waste recycling (Revellame et al, 2021). Since the beginning of human spaceflight missions, algae have been considered promising candidates for space life support systems due to their rapid growth rates, the fact that they are straightforward to grow, and edible biomass (Powell et al, 1961; Rangel-Yagui et al, 2004; Soletto et al, 2005; Ganzer and Messerschmid, 2009; Wells et al, 2017). Various experiments have been conducted to study the effects of radiation, microgravity, space vacuum, and temperature extremes on algae growth for space exploration missions (Horneck et al, 2003; Thirsk et al, 2009), and it has been shown that algae are capable of surviving exposure to spaceflight conditions (Niederwieser et al, 2018)
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