Oxygen sustaining the astronauts during such long-term missions cannot be
carried in sufficient quantity. Depending on activity a 75-kg human needs about
700 to 1000 L of oxygen per day (Montoye et al. 1983). Likewise, the exhaled
carbon dioxide needs to be removed from the air in addition to nitric oxide and other
trace gases (Dweik et al. 1998). NASA is currently using solid amine sorbent and
zeolite 5A molecular sieve material packed into beds for removing carbon dioxide
during extended space flights (Satyapal et al. 2001; Knox et al. 2015).
The combined problems led to the concept of recycling these materials during
extended space flights using bioregenerative life support systems (Blüm 2003; Wang
et al. 2006). Based on photosynthetic algae or plants these systems can absorb
carbon dioxide, produce oxygen and remove wastes such as ammonia (Yang et al.
1997; Sakano et al. 2002). In addition, advanced ecological life support systems may
even be used for crop production for human consumption such as vegetables
(Wheeler and Sager 2006).
8.2 Aquarack
In preparation of space flights it was proposed to carry out a long-term experiment
growing flagellates in a closed bioreactor (Häder and Kreuzberg 1990). The unicellular green flagellate Euglena gracilis was inoculated in autoclaved tap water in a
10-L bioreactor (Braun Biotech, Melsungen, Germany; Porst et al. 1997). The
density was adjusted to 1.7 10
5 cells/mL. The reactor was completely closed with
no additions of nutrients, and light was the only energy source. Measurements were
performed using a closed-loop concept without taking samples. Cell suspension
from the bioreactor was pumped through two loops. In one loop the cell suspension
was pumped through a vertically oriented, circular viewing chamber which allowed
observing the cells under a microscope with an attached CCD camera. Cell density,
motility and orientation were analyzed by a real-time image analysis program (Häder
1994). Also in this loop was a flow-through cuvette to perform absorption measurement via a glass-fiber cable connected to a microspectrometer (Ocean Optics Inc.,
USA). In a second loop the cell suspension was permanently pumped through
an electrode holder for on-line water analysis at a flow rate of 15 L/h. Oxygen
concentration was determined with a Clark electrode and nitrate with an Orion
(Model 83-07) electrode; in addition, the pH was determined on line (Lebert et al.
1995). The signals were amplified and recorded after A/D conversion. Under three
fluorescence lamps (mixed cool white and warm tone, 20 W m
À2 ) the flagellates
produced about 3.9 mg oxygen per hour which increased to 10.3 mg/h with nine
lamps. Because the cells also consumed oxygen by respiration the concentration in
the bioreactor was constant at about 8.5 mg/L (Lebert and Häder 1998). The duration
of the long-term experiment was more than 600 days.
During the first 5 months the cell density slowly increased up to 3.5 10
5 cell/mL,
subsequently decreased to the initial value (1.7 10
5 cells/mL) after 10 months and
thereafter was stable for another 11 months. Because no nutrients had been added,
114
8 Bioregenerative Life Support Systems in Space Research
carried in sufficient quantity. Depending on activity a 75-kg human needs about
700 to 1000 L of oxygen per day (Montoye et al. 1983). Likewise, the exhaled
carbon dioxide needs to be removed from the air in addition to nitric oxide and other
trace gases (Dweik et al. 1998). NASA is currently using solid amine sorbent and
zeolite 5A molecular sieve material packed into beds for removing carbon dioxide
during extended space flights (Satyapal et al. 2001; Knox et al. 2015).
The combined problems led to the concept of recycling these materials during
extended space flights using bioregenerative life support systems (Blüm 2003; Wang
et al. 2006). Based on photosynthetic algae or plants these systems can absorb
carbon dioxide, produce oxygen and remove wastes such as ammonia (Yang et al.
1997; Sakano et al. 2002). In addition, advanced ecological life support systems may
even be used for crop production for human consumption such as vegetables
(Wheeler and Sager 2006).
8.2 Aquarack
In preparation of space flights it was proposed to carry out a long-term experiment
growing flagellates in a closed bioreactor (Häder and Kreuzberg 1990). The unicellular green flagellate Euglena gracilis was inoculated in autoclaved tap water in a
10-L bioreactor (Braun Biotech, Melsungen, Germany; Porst et al. 1997). The
density was adjusted to 1.7 10
5 cells/mL. The reactor was completely closed with
no additions of nutrients, and light was the only energy source. Measurements were
performed using a closed-loop concept without taking samples. Cell suspension
from the bioreactor was pumped through two loops. In one loop the cell suspension
was pumped through a vertically oriented, circular viewing chamber which allowed
observing the cells under a microscope with an attached CCD camera. Cell density,
motility and orientation were analyzed by a real-time image analysis program (Häder
1994). Also in this loop was a flow-through cuvette to perform absorption measurement via a glass-fiber cable connected to a microspectrometer (Ocean Optics Inc.,
USA). In a second loop the cell suspension was permanently pumped through
an electrode holder for on-line water analysis at a flow rate of 15 L/h. Oxygen
concentration was determined with a Clark electrode and nitrate with an Orion
(Model 83-07) electrode; in addition, the pH was determined on line (Lebert et al.
1995). The signals were amplified and recorded after A/D conversion. Under three
fluorescence lamps (mixed cool white and warm tone, 20 W m
À2 ) the flagellates
produced about 3.9 mg oxygen per hour which increased to 10.3 mg/h with nine
lamps. Because the cells also consumed oxygen by respiration the concentration in
the bioreactor was constant at about 8.5 mg/L (Lebert and Häder 1998). The duration
of the long-term experiment was more than 600 days.
During the first 5 months the cell density slowly increased up to 3.5 10
5 cell/mL,
subsequently decreased to the initial value (1.7 10
5 cells/mL) after 10 months and
thereafter was stable for another 11 months. Because no nutrients had been added,
114
8 Bioregenerative Life Support Systems in Space Research