Plants must be grown in special growth chambers aboard the ISS. The astronauts run experiments on both the plants and the growth chambers, trying to learn about and improve the process of space farming.

Photo courtesy NASA

The Challenges of Space Farming

To understand the challenges of space farming, let's consider some of the elements that affect plant growth in space.

Less Gravity

Current space-farming experiments examine different aspects of farming in microgravity (a term to describe an environment with little or no gravity). These experiments could be helpful in the related case of farming on the surface of the moon or Mars, which have significantly lower levels of gravity than Earth. Plants take their cues from gravity for aspects of their growth, such as root and stem orientation. Scientists analyze whether plants can properly grow with lower levels of gravity, and just what those levels are.

Artificial Lighting

Most plants on Earth have access to loads of natural sunlight and grow toward that light, but researchers must fool plants growing in space to follow this same behavior. The choice of lighting in the growth chambers is an important consideration for several reasons. It's important to use energy efficiently in space, because resources are limited. Energy can't be wasted on light bulbs that don't maximize their output. In addition, different types of lighting create different levels of heat, and extra heat is something spacecraft must eliminate (researchers prefer bulbs that produce little heat). Additionally, astronauts don't have extra room to lug spare light bulbs through space, so they need a lighting source with staying power, like light emitting diodes (LEDs).

Varying Rooting Materials

Little to no gravity can affect how rooting materials function. Different rooting materials and soils are better than others when it comes to water and air distribution -- both key to successful plant growth. Out in space, grainy soils can cause water to scatter and fine soils can prevent airflow [source: Franzen]. Researchers are experimenting with many possibilities, including clay particles, hydroponics and a material like peat-moss.

Contaminants

Plants grow by using the spacecraft's air, humidity and microgravity -- conditions that are different from those on Earth. Researchers are studying whether any contaminants and dangerous organisms from space will affect those space-grown plants, making them inconsumable for humans. Changes in their genetic codes could be harmful in other ways. There's a possibility that if astronauts brought the plants back and mixed them with those grown on Earth, we might end up with the space-version of kudzu. Kudzu (Pueraria montana) is an invasive species of plant, brought to the U.S. from Japan in the late 1800s.

Limited Available Space

The confined quarters of spacecraft are very different from the massive, rolling farmlands on Earth. Researchers must develop an efficient, streamlined apparatus that can hold crops as they grow with limited space. Growing machines must be automatic (or at least have that capability) and be able to regulate watering, humidity, lighting, air circulation and nutrient delivery. These growing machines also need to integrate with the life support system to successfully exchange carbon dioxide and oxygen.

So when can astronauts visit space's first salad bar? It might be a while as researchers work to understand and overcome the obstacles that space farming presents. Read the next page to learn about their research and why insects might become space food of the future.