LED lighting optimization as applied to a vitamin space plant growth facility.

An algorithm of determining optimal LED lighting parameters for leafy crops (Chinese cabbage Brassica chinensis L. was taken as a model) in a vitamin space Plant Growth Facility is proposed. The lighting parameters to optimize were the level of photosynthetic photon flux density (PPFD), red and white LEDs PPFD ratio and pulse repetition period with a fixed pulse length 30 µs. Optimal lighting parameters should allow achieving a high biomass yield per consumed light energy, as well as high vitamin C content in the crop biomass. A quantitative optimality criterion for estimating the lighting parameters quality is suggested. For Chinese cabbage crop the maximum value of this criterion was obtained at the following lighting conditions parameters: PPFD - 500 µmol m-2 s-1, red/white ratio - 1.5, and pulse repetition period - 501 µs.

SUBSTANTIATION OF OPTIMAL LIGHTING REGIMES FOR PLANTS IN SPACE GREENHOUSE <>.

A 3-factor experiment with 24-d vegetation of Brassica chinensis L. crops demonstrated the dependence of dry mass yield on lighting regimes provided by a lamp composed of white (color temperature 4000 K) and red (660 nm) LEDs (light-emitting diodes). Experimental data were used to build regressive dependences of plant dry mass and optimal light criterion (product of dry mass and photosynthesis efficiency) on 3 LEDs lamp parameters: photosynthetic photon flux density (PPFD), red and white PPFD ratio, and pulse period. The following LEDs light parameters were found to be optimal for the Chinese cabbage: time-averaged PFD - 500.µmol/(m².s), red and white PPFD ratio - 1.5 and pulse period - 501 ps. Considering the wattage rating for projectible vitamin greenhouse Vitacycle-To, continuous light should have PPFD = 430 pmol/(m²-s), rPPFD/wPPFD ratio - 1.5 and continuous light.

[Results of salad machine experiment within the MARS-500 project].

The salad machine experiment was aimed to fulfill performance testing of a prototype of space conveyor-type cylindrical greenhouse PHYTOCYCLE-SL, to study growth and development of plants, and to evaluate microbial contamination of equipment in the closed manned environment. Crops of leaf cabbage Brassica chinensis L., cultivar Vesnianka were raised in the time interval between MARS-500 days 417 and 515. The greenhouse proved it serviceability demanding 17 min/(man x d) in the normal mode. Most likely that the slow growth rate and deviations in plant morphology were caused by the presence of volatile pollutants in the greenhouse compartment Accumulation of micromycetes was observed at the sites of humid surfaces contact with ambient air; reduction of the artificial soil area contacting with air decreased population of micromycetes in 40 times. Cabbage leafs were free of pathogenic microflora. These results of the experiment helped develop recommendations on how to work out some units and systems in projectable greenhouse VITACYCLE-T

[Greenhouse with a convex spherical planting surface as a prototype of space greenhouse and an instrument for studying the plant gravitropism].

IBMP has developed a technology and unit for cultivating self-opening crops on a convex planting surface illuminated by light-emitting diodes mounted on an external concentric panel ("Hemisphere"). The unit has a structure of two-member clinostat with semispherical plant growth chamber with a 600-mm diameter and a speed of from 1 to 10 revo about each axis; water potential in the root supply system is maintained at 1.0 +/- 0.45 KPa. Having the data of 1200 measurements in the growth chamber, PAR latitude and meridian gradients were determined which did not exceed 0.7 micromol/(m2 x s x cm) in the work area and differed from the radial gradient by order and, therefore, had a negligible contribution to the axial organs' deviation from the radial directions during laboratory tests. Maximal centrifugal acceleration was equal to 10(-10) of the acceleration of gravity and did not impact the gravitropic crop reactions in the growth chamber. Five 5-day tests with semidwarf wheat Triticum aestivum L., cult. Lada were performed in the "Hemisphere" growth chamber turned at different angles relative to the gravity vector. In immobile growth chamber plants inclination from the vertical was a function of the angle between the PAR gradient and vector and the gravity vector at the site of each seed. Crop rotation at 3 revo about the horizontal axis did not produce noteworthy plant inclination suggesting neutralization of the plant geotropic reactions. In all tests about 80% of the plants formed the first leaf and about 20% reached the coleoptiles phase. Morphometric differences in the tests were insignificant. On a balance, the tests showed that prototype of space greenhouse "Hemisphere" is fit to run laboratory investigations of the plant gravitropic reactions in both static and dynamic conditions.

[Prototype of space vitamin greenhouse "Phytoconveyor"].

Installation of a greens production system on the International space station will mean a leap toward biological regeneration of food in long-duration space mission. Today, priority is given to green cultures as supplements of space rations and a psychological support to crews in exploration missions to Mars, and also as least resource-intensive. Cylindrical salad greenhouse "Phytoconveyor" designed at the Institute for Biomedical Problems is highly productive, energy-efficient, and requires minimum of crew time for. Dimensions of the greenhouse are 540 x 590 x 400 mm, power demand is 0.25 kW, and the Plant chamber volume is about 0.09 m3. 'Phytoconveyor" has a planting unit with six cylindrical root modules. The total illuminated crop area is about 0.4 m2. The lighting unit consists of red (660 nm) and blue (470 nm) light-emitting diodes on the inner surface of a spiral cylinder coaxial with the roots module unit that generate the photon flux density 350 micromol x M(-2) x s(-1) at a distance of 4 cm. Each root module has a porous tube wrapped up in a fiber substrate with ion-exchange resins and is covered with a lightproof plastic with seed slits. The "Phytoconveyor" design includes a programmable reverse watering system. Given the 24-hr light period, the laboratory model of "Phytoconveyor" can produce up to 300 gram of fresh greens every 4-5 days. The greenhouse was designed with due account of resource limitations on the ISS Russian orbital segment.

[Analysis of characteristics of a salad space greenhouse with a diode lighting unit].

The laboratory model of space production salad conveyer PHYTOCYCLE SD utilizes the principle of self-opening of plants growing under the light-emitting diodes. A computer model has been proposed to estimate greenhouse productivity as a function of design values. The model was used to compare greenhouses with a cylinder and flat crop surface. Self-opening crops on the cylindrical surface were shown to have a 30% advantage in production per a unit of light energy. Based on the analysis of the dependence of specific productivity on light intensity, the most effective light level is 300-350 micromol x m(-2)s(-1). It was established that PHYTOCYCLE SD productivity per a unit of orbital resources is much better compared with the known research plant growth facilities and can meet the vitamin (A and C) and rough dietary fibers' demand of three crew members.