In the upcoming launch of space shuttle Discovery this coming Saturday, astronauts would have a lot of travel companions. Thousands of fruit flies are also going aboard the shuttle to participate in an experiment that would aim to know how space messes with the immune system.

Trivia: Fruit flies are space pioneers. They were the first animals flown in space, inside a U.S. V2 rocket in 1946 to assess the effects of radiation. Fruit flies have been racking frequent flyer miles to space since they regularly board Russian and U.S. missions ever since.

So how will the experiment go? NASA will send one tray of adult fruit flies and another of embryonic flies that will mature into adult flies by the time the shuttle lands at the end of its 12-day mission. Aside from that, test tubes full of a fungus called Beauveria bassiana also will fly.

After the mission, both sets of flies, along with a genetically identical control set of flies grown at NASA's Kennedy Space Center, will be exposed to the space-exposed fungus to test their immune system responses.

Scientists will be in the know about the flies' immune response through observing cell counts and measures of blood-clotting ability and of compounds produced to eliminate the fungus. The study will also look at the progression of cancerous and benign tumor cells in the flies, as the radiation of space increases the risk of cancer in astronauts. Past experiments reveal that near-weightlessness of spaceflight affects an astronaut's biology and bugs that cause various medical conditions.

Fruit flies were chosen to participate in this experiment because they make good model organisms for studying such processes as the effect of space radiation on human genetics and immunity. Fruit flies have short life spans, reproduce quickly, and eat next to nothing, and their DNA mutates rapidly.