A Green Thumb for Astronauts

(L-R) Shudong Wu, head of the Applied Research Laboratory's electro-optic group, Edie Sears, graduate student, and technology specialist Edmond Pope examine an AOTF spectrometer, which can scan thousands of shades of light in milliseconds.

A research project designed to help astronauts survive extended journeys into space may benefit farmers, greenhouse operators, environmental professionals, and others who depend on and care for plants. Edie Sears, a doctoral student in agricultural and biological engineering, was selected from among more than 100 applicants to receive funding for her research in the area of Advanced Life Support from the National Aeronautics and Space Administration. "Extended space travel will require an enclosed environment or life support system that is bioregenerative," Sears says. "Plants would play a critical role in recycling nutrient wastes, filtering water, and providing food and oxygen for crew members. These plants would have to be monitored carefully to make sure they stay healthy enough to keep the system working properly." Sears and her adviser, agricultural engineer Paul Walker, are on their own mission to find an easy way for astronauts to monitor plant stress. Using computers and new remote sensing technology, Sears is developing an automated system that measures various stresses on plants in a growth chamber by interpreting how their leaves reflect and respond to different sources of light.

Sears is well prepared to tackle this project. After receiving a bachelor's degree in biological systems engineering from Virginia Polytechnic Institute, she completed a study for her master's degree at Penn State that focused on reducing the mass and size needed for a spacecraft's life support system by reducing the time it takes to recycle plant nutrients. Sears also led an interdisciplinary group of four students working on a Pennsylvania Space Grant Consortium project to manipulate canopy lights to increase plant productivity.

In her current project, Sears will be studying the detection of chlorophyll fluorescence, which provides an indication of stresses that may be affecting plant photosynthesis. "When a high-intensity light source irradiates plant tissue, it puts energy into the plant," Sears says. "This energy either gets stored as a photosynthetic chemical or is emitted in the form of fluorescence or heat. If photosynthesis is affected by disease, nutrient deficiency, or other stresses, more energy is converted into heat and fluorescence, and the resulting spectra may be used as a stress indicator. Initially, we will look for plant stress caused by poor nutrition, but the final design will have the capacity to detect other stresses, like disease."

The traditional laboratory technique for detecting chlorophyll fluorescence includes securing a leaf in place with clips, directing a high-intensity beam onto the leaf, and monitoring the resulting fluorescence. "This technique is not fully automated, nor does it reveal the status of the entire plant," Sears explains. "Taking measurements from the whole plant canopy will provide a faster, more comprehensive evaluation of the plants' condition."

Sears' project takes advantage of an acousto-optical tunable filter (AOTF) spectrometer, which was designed by Russian scientist Vladislav Pustovoit and was brought to Penn State's Applied Research Laboratory by foreign technology specialist Edmond Pope. "When I mentioned the device and its capabilities to Paul Walker, he told Edie about it, and they came up with this great project," Pope says. "With a relatively new technology like this, solving one problem can have a domino effect on finding other practical applications, such as in agriculture. The Russian scientists who developed the AOTF spectrometer really like this connection."

Scientists use spectrometers to measure wavelengths of light. "Conventional spectrometers are not very portable," Sears says. "The AOTF spectrometer is ideal for monitoring plant stresses during an extended space mission because it has no mechanically moving parts, which makes it small, fast, and reliable. It fits in my hand, and has faster scanning capacity than older types. It can detect thousands of distinctive shades in milliseconds. It also can be calibrated or tuned very rapidly, so it can be set up in only 10 minutes or less. It doesn't even require much power."

AOTF spectrometers can cover a wider range of light than many instruments. "They are able to detect wavelengths from ultraviolet to infrared spectra," says Shudong Wu, head of the Applied Research Laboratory's electro-optic group and associate professor of electrical engineering. "The instrument has been used in space before, so it's already proved its durability."

The canopy-scanning technique could be ideal for many applications on Earth. "This project will take place in a small growth chamber so we can see if it works at a microcosmic level," Sears explains. "If it does, the same technology could be adapted to evaluate much larger systems, including plants in greenhouses, crops on farms, and even entire forests."

–Eston Martz