· Basic Sciences: gravitropism, phototropism w/o gravity, radiation biology, gravitational biology (effect of gravity on growth, photosynthesis, materials properties, secondary metabolites, productivity, disease, genetic research,…
· Applied Research: materials (lignin, cellulose), drugs (derived pharmaceuticals),
·
Life Support: food production, fresh food, psychological
‘green thumb’, air revitalization, water purification.
See also: Factors
affecting plant growth
· Light
· Atmosphere
o Photosynthesis (day, sufficient light, green plant shoot) / Respiration (night, germination, low light, roots): Carbon dioxide, Oxygen
o Temperature, humidity and pressure
o Trace contaminants
o Air flow (mixing, heat transfer / ‘swamp cooler’), bending / shaking – affects plant morphology
· Water and Nutrients
o ‘root attachment’: access to water/nutrients
o water distribution and recovery
· Life Support: high edible mass, fast growth, wide environmental compatibility, nutritious, flavor, low processing needs
· Plant Biology: well characterized, environmental compatible
o Arabidopsis
– European Cress, fast growing, genome characterized, many mutants,
http://www.arabidopsis.org/,
http://www.arabidopsis.com/ http://afgc.stanford.edu/
o Wheat (life support applicability), lettuce, soy
bean, pine, …..
Wisconcin Fats Plants: http://www.carolina.com/fastplants/
http://www.fastplants.org/home_flash.asp
· Sunlight spectrum UV to IR, 1390 W/m2 extraterrestrial, 400-700 nm visible.
o Full sunlight on earth: »2,000 umol/m2/s PAR (400-700 nm), »440W/m2,1,000 W/m2 full surface radiation), 100,000 lux (human eye only)
· Known plant absorption blue and red (photosynthesis), UV-Blue-Red-Far-red(735nm) and ratios to each other (photomorphology)
o Photosynthesis: energy conversion; mainly red and blue, quantum energy)
o Photomorphogenesis: elongation (blue = short), germination (red, red-far-red ratio),
o Photoperiod (short-day, long-day), continuous light, day/night cycle, productivity.
· Artificial light: efficiency of electric energy to energy available to plants (leaves):
o Lamp efficiency, distribution (point source, line source, area source) / reflectors
o Systems engineering: operating temperature, usable spectrum: IR (heat radiation), blue content, life time bulb
· Natural light: accessibility (safety, orbit), availability (time)
o Clear light transmission – window / frangible
o availability (day/night cycle LEO 40/50min of 90 min/revolution, 14day/14night moon)
o distance to sun
· CO2 and Oxygen – consumables
o Earth ‘typical values’: CO2: 380 ppm v/v (0.038%); 21% O2
o Too much O2: toxicity, flammability, competitive binding of CO2
· Moisture content – evapotranspiration – transpiration = cooling, evaporation = excessive load on humidity control / loss.
o Typically 70% = “normal”; too high: reduced leaf evaporative cooling, mildew growth,..; too low: increased evapo-transpiration.
o Vapor pressure – water at 25°C = 23.76 mmHg / 2.985 kPa.
· Temperature – too low – slow growth, too high – death; plant growth very temperature-dependent; species-specific needs / optima
o Typically 18-25°C, some plants to 30°C; most spaceflight experiments at 22-25°C
· Pressure – low pressure plant growth possible; increased water loss, reduced heat transfer;
o Hypobaric plant growth, low pressure plant growth,
· Trace contaminants – harmful to plants: offgassing and biogenic production
o Ethylene – plant hormone
· Air flow: in microgravity w/o convection: needed for mixing, cooling, but: mechanical excitation, bending w/o gravity
o Earth green house: recommend < 1 m/2;
o space green house: < 0.1 m/s; vertical up / uniform distribution; no side bending (gradients, uncompensated mechanical stimuli)
· Containment, control / transport / distribution in ‘soil’ w/o gravity
· Water content sensing
· Nutrient Delivery Systems
· Nutrient content (salts – materials compatibility, clogging / crystallization), concentration / pH maintenance.
o Electric conductivity (1/R = 1/Ohm = Mho = Siemens); typical nutrient solution (hydroponics: about 2 mS/cm)
o pH (solubility changes with pH, fall-out; typically 5-6)
o composition: macro- (N: nitrate or ammonia, P: PO4-, K” potassium) and micro-nutrients (iron, zinc,…)
o macro
(> 10 ppm): N, P, K
o micro (< 10 ppm): Ca, Mg, Fe, Mn, B, Cu, Zn, Mo,
· Root attachment:
o Hydroponics, ‘soil-less’ – Rockwool, Vermiculite, Zeolite, Fibrous Ion-exchange Mats
o Soil – pore / grain size, nutrient composition
o Aeroponics – water mist
o Porous tube NDS