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A reliable nutrient delivery system is essential for long-term cultivation of plants in space. At the Kennedy Space Center, a series of ground-based tests are being conducted to compare candidate plant nutrient delivery systems for space. To date, our major focus has concentrated on the Porous Tube Plant Nutrient Delivery System, the ASTROCULTURE™ System, and a zeoponic plant growth substrate. The merits of each system are based upon the performance of wheat supported over complete growth cycles. To varying degrees, each system supported wheat biomass production and showed distinct patterns for plant nutrient uptake and water use.

The first spaceflight opportunities for Advanced Life Support (ALS) Project testing with plants will likely occur with missions on vehicles in Low Earth Orbit, such as the International Space Station (ISS). In these settings, plant production systems would likely be small chambers with limited electrical power. Such systems are adequate for salad-type crops that provide moderate quantities of fresh, flavorful foods to supplement the crew diet. Successful operation of salad crop systems in the space environment requires extensive ground-based testing with horticultural methodologies that meet expected mission constraints. At Kennedy Space Center, cultivars of radish, onion, and lettuce are being compared for performance under these “flight-like” conditions.

A primary challenge for supporting plants in space is to provide as much photosynthetically active radiation (PAR) as possible, while conserving electrical power. Light-emitting diodes (LEDs) and microwave lamps are innovative artificial lighting technologies with several appealing features for supporting plant growth in controlled environments. Because of their rugged design, small mass and volume, and narrow spectral output, red and blue LEDs are particularly suited for outfitting plant growth hardware in spaceflight systems. The sulfur-microwave electrode-less high-intensity discharge (HID) produces a bright broad-spectrum visible light at a higher electrical conversion efficiency than conventional light sources. Experiments compared the performance and productivity of spinach (Spinacia oleracea L.) grown under conventional lighting sources (high-pressure sodium and cool-white fluorescent lamps) with microwave lamps and various wavelengths of red LEDs.

Under certain nutrient solution management practices in hydroponic systems, sweetpotato [Ipomoea batatas (L.) Lam.] plants can exhibit excessive shoot growth and reduced storage root yield. An experiment was conducted which compared sweetpotato production in nutrient film technique (NFT) systems either with daily nutrient solution replenishment + real-time pH control or with nutrient solution replenishment 3-times per week + periodic pH adjustment. Results showed that replenishment of nutrient solution on a daily basis produced excessive foliage growth with very little storage root production. Nutrient solution replenishment 3-times per week produced manageable vine growth and respectable storage root yields.