Other experiments were designed to examine blood, urine, and saliva samples taken before, during, and after the mission.
Feeback says protecting astronauts from cosmic and solar radiation is the biggest threat scientists must overcome to ensure crew safety during long-duration spaceflights.
"Radiation damage can cause lots of problems," he said, noting that it can impair astronauts' cognitive ability, damage their immune systems, and increase the risk of cancer.
(Related online feature: Exploring Space in National Geographic magazine.)
Jeanne Becker is the associate director of the National Space Biomedical Research Institute in Houston, a consortium funded by NASA to study the effects of spaceflight on human health.
She says the zero gravity of space is so foreign to the human body that health issues are certain to arise.
"The body is an amazing machine, absolutely. But we all developed in a one-G environment," she said, referring to the scientific term for the force of gravity on Earth.
"So when we go up and expose our body to almost zero gravity, there are changes in some physiological systems."
In the case of pedestrians on Earth, gravity pulls heavily on the lower body. But in space, astronauts float, using their arms more and their legs less.
Becker notes that with less gravity pulling on astronauts' lower extremities, fluid shifts and pools toward the upward region of their bodies.
"These are really big changes the [body] is adapting to," Becker said.
Bone-loss also accompanies this gravitational "unloading" on the lower body. As a result, Becker noted, "there are increasing levels of calcium present that can sometimes result in increasing [kidney] stone risk."
Astronauts now routinely exercise in space to counteract the bone and muscle loss experienced in spaceflight.
But whether room for such equipment will be available on next generation spacecraft is an open question, Feeback says.
"We may have to have an engineering solution rather than a physical solution," he said.
Astronauts, for example, may have to accept a certain amount of bone and muscle loss during a flight to Mars.
But when they reach the red planet, they might don a spacesuit with built-in artificial muscles to complete mission objectives, such as building a structure.
Feeback says long-duration space missions may also require NASA managers to select flight crews based on their brawn as much as their brains.
"No one really likes to talk about itwe want the brightestbut sometimes the brightest aren't the most athletic," he said.
Becker says scientists are also paying close attention to the effect of spaceflight on mental health.
"Imagine going on a Mars mission where you're going to be out of touch from friends and family for a very long period of time. These are very real factors that affect emotional well-being," she said.
The sleep research from the latest Discovery mission should address some of these issues, Becker says. Unusual sleep patterns are a common sign of emotional stress.
A host of other Earth-based experiments have been designed to simulate the emotional challenges astronauts face in space.
For example, a NASA Extreme Environment Mission Operations experiment put several aquanauts in a tight-quartered underwater habitat and forced them to work together to solve problems.
Understanding how the aquanauts work in isolated underwater environments allows scientists to prepare astronauts for working together in space, Becker says.
"We need to have good working dynamics among the crew," she said.
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