Engineers and plant scientists at the University of Arizona in Tucson, Ariz., and Sadler Machine Co. in Tempe, Ariz., have designed and built a largely automated, self-contained hydroponic Food Growth Chamber (FGC) capable of producing as many as 10,000 heads of lettuce (2,500 pounds) a year, or a mixture of lettuce and tomatoes, green peppers, cucumbers, and herbs. That has proven a benefit not only to the health, but also to the morale, of the 200 people working at the Amundsen-Scott South Pole Station.

"There's real sensory deprivation out there," says Philip D. Sadler, founder of Sadler Machine Company.

Under a three-year, $425,000 contract with Raytheon Polar Services Company, the partnership built the chamber in Tucson, tested it, took it apart, and shipped it in boxes to the South Pole. There the chamber was installed within the new 65,000-sf elevated building constructed as part of a $168-million upgrade of the station.

The facility that the station is replacing—a collection of seven buildings inside a geodesic dome—contained the original low-tech version of the chamber built by Sadler and his volunteer crew.

"This is a very sophisticated upgrade to that," says Sadler.

High-Tech, Low Maintenance

The chamber was designed with one overarching concern: That it be sophisticated enough to be productive, yet automated enough be run by volunteers who are at the South Pole primarily as scientists and their support staff. Operators receive training at the University of Arizona, Controlled Environment Agriculture Center (CEAC) before being deployed for Antarctica. Further instruction comes from the operating guide and tele-training on site.

"You can't expect people who are there for other things to go in and maintain the structure and fix the components," says Dr. Gene A. Giacomelli, director of the CEAC. "It needs to be semi-automated, or in some cases, fully automated. It should take just a few minutes a day of their time."

Crew changeovers generate a learning curve every season, and the automated system and remote access help keep the chamber operational during this time. Production also is greatly improved by the continuous automated monitoring. Manually, monitoring could only be done once a day, thereby greatly reducing production.

The temperature, humidity, light intensity, and CO₂ concentration in the chamber, as well as the pH and fertilizer content in the plant nutrient solution, are monitored remotely via a Web-based system at the CEAC. A live Web cam allows the UA staff to look into the chamber when satellite access is available. Digital photos in email messages can be used to help diagnose problems.

"If they go off-nominal, we try to diagnose the problem and talk them through repairs either by email, phone, or most recently by Web cam," says Giacomelli.

The system also is monitored on site, with problems noted on a computer screen. If a problem is serious, such as the plant lights overheating, a horn sounds and warning lights flash in the hallway outside the chamber.

The insulated chamber—which is roughly 27.5 feet long, 13.5 feet wide, and 8.5 feet tall—is constructed of aluminum panels which interlock to create the outer walls, ceiling, and floor. The floor is covered with ⅛-inch-thick aluminum plate. The chamber is self-contained within the South Pole Station, but allows for integration with station resources, utilities, and personnel.

The food growth system has three components: a 252-sf production room, a 140-sf "Enviro-room," and a 112-sf utility room. The chamber itself includes the production room, where most of the plants are grown, and the Enviro-room, where hobbyists can grow their own edible plants. A dividing wall separates the two rooms of the chamber and maintains a controlled gas exchange across the production room boundaries. The wall consists of aluminum frame construction with glass panels and doors that allow people to spend time in the Enviro-room with full view of the production room without needing to enter it. The dividing wall also serves as the conduit from the utility room to the production room and Enviro-room for all utilities, including HVAC; chilled and hot water; plant nutrients and water; and wiring for power, data collection, and control. The utility room, where hardware and consumables are kept, is a 4-foot-wide space accessed through the main hallway.

The Food Growth Chamber looks more like a laboratory than a backyard greenhouse. The center of the production room contains long troughs of vegetables poking out through holes in a white plastic cover. Along the walls are two rows of smaller white trays on racks that adjust to accommodate the height of the plants. The lower racks slide in to allow people to create an aisle between them and the center troughs. When the room is unoccupied, the bottom trays are pulled out so they can benefit from the overhead lights. The lighting is artificial, and there is no dirt involved in the planting. (A multinational treaty limiting the use of Antarctica for peaceful scientific purposes prohibits bringing soil to the continent in order to preserve its unique and pristine ecosystem.) The plants are fed hydroponically, with a system of flowing water infused with just the right mixture of nutrients for each variety of plant.

Giacomelli won't even call it a greenhouse.

"To me, a greenhouse is a structure that uses the sun," says Giacomelli. "This is inside a building standing out there on the ice in the Antarctic."

Liquid Diet

The nutrient delivery system is fully automated. The nutrients are constantly monitored and maintained in the nutrient storage tanks by the "fertigation" component in the utility room. Nutrient water is pumped to each tray or trough, and unused nutrient water is returned to a storage tank located below. Using a "double-pass design," the nutrient flows into one end of the tray, past the roots of the plants to the opposite end, and then returns underneath the plants to the original end. This provides the greatest distance between the last plant and the drain hole, preventing the roots from clogging the drain.

The short growing trays are designed to be completely removed from the chamber for harvesting. The tray is taken to the kitchen, which is better equipped for messes, where the plants are harvested and the tray is cleaned and re-seeded.

Three tanks—A, B, and C—contain stock solutions A (nutrients), B (nutrients), and C (acid). The nutrient solutions are mixed with water to a concentration ratio of 200:1. The pH of the nutrient solution is controlled by the amount of acid from tank C. When in operation, nine peristaltic pumps deliver approximately 12 milliliters of solution per minute to the mixing block: Three double-gang pumps deliver solution A, three deliver an equal amount of solution B, and three single-gang pumps deliver acid in the amount needed.

As the nutrient solution is returned to the tanks from the plant reservoirs, a small plastic tube line diverts some of the nutrient to the mixing block, where sensors test it for electrical conductivity (which indicates the concentration of stock solution in the water) and pH. If the solution is out of balance, more stock solution or acid is automatically pumped into the mixing block.

The mixing block is separated in to three chambers, one for each of the three growing systems in the production room. Each system has different types of plants, so each requires different nutrients and pH. Each chamber is then divided into two sections, one with sensors for testing the pH and electrical conductivity, and a second one downstream for remixing to correct the content of the stock solution and acid.

Each of the three tanks can hold a maximum of 100 gallons, which is constantly filtered and replenished as the plants consume it. In theory, the system can work continuously without ever dumping the nutrient solution, but that requires a much more complex setup than is reasonable for volunteers to maintain, says Giacomelli. In this case, the system water may be replaced as infrequently as twice a year.

"You can stop adding fresh water for a few days prior to changing, and that will cut the volume of wastewater in half," he says.

Manufactured Sunshine

The plants get their light from 12 1,000-watt, water-cooled, high-pressure sodium lamps. The water-jacketed lighting system collects as much as 60 percent of the heat generated by the high-intensity lighting, and removes it from the chamber. That prevents the excess heat from overworking the HVAC system, and allows plants to grow in closer proximity to the lamps than if they were not water-jacketed. The lights are 10 times more powerful than a 100-watt bulb, but are cool to the touch.

The lights consist of a double-ended high pressure sodium lamp, surrounded by an annulus shaped quartz jacket mounted in an aluminum bracket with a reflector. Supply and return lines connect to the glass jackets and cycle de-ionized water past the lamps. The water needs to be de-ionized because any chemicals, such as copper, in the water will plate out, explains Sadler.

"The chemicals will turn the jacket black and deposit themselves on the glass, reducing their light output," he says.

Each light is equidistant from the pump, providing an equal flow of about one liter per minute to each lamp. As dissolved gasses come out of solution at the surface next to the bulb, the bubbles are vented at the highest point in the system.

The lamps are never operated without the water-cooling system, and the water cooling system is never shut down, even when the lamps are not operating. This eliminates the possibility of the lamps erroneously being used without the cooling system. Sensors within the computer control system continually monitor the flow, temperature, and pressure of the cooling-water. If any parameters become out of desired range, either a warning is given and/or the lamps are shut down automatically.

The air in the production room is enriched with CO₂, so it is important that workers enter the room as infrequently as possible in order to maintain the proper balance. Pipes carrying the plant nutrients protrude into the Enviro-room, where the pipes are capped. This allows the nutrient flow to be monitored from the Enviro-room without entering the production room.

The Enviro-room is a sitting room where station workers can relax in an atmosphere of elevated humidity and lighting in view of the plants growing in the production room. It also contains some growth tanks where workers with a penchant for gardening can grow their own edible plants, such as herbs and small vegetables. An unexpected feature of life at the South Pole is that the environment is devoid of smells; the Food Growth Chamber is one of the few places at the station where they can get relief from their sensory deprivation.

So far, these Food Growth Chambers have been installed only at the South Pole and at the McMurdo Station in Antarctica, but Giacomelli and Sadler are pursuing their use in supporting crews in other isolated locations, as well as in space. They have developed growing systems in an inflatable greenhouse for use on Mars, and are designing lunar greenhouses, which would be buried below the lunar regolith (soil) on the moon.

By Lisa Wesel

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