(T-G Photo by John I. Carney) [Order this photo]
Seddon, a veteran of three space shuttle missions, appeared as part of the school's Follin Speaker Series. With the help of video footage, she told the story of STS-40, a 1991 mission dedicated to research in life sciences during which she and her crewmates performed a series of experiments testing the effects of space travel on humans -- and on some of the shuttle's other passengers, several laboratory rats.
Seddon was one of the first six women in the astronaut program, part of the first class of astronauts that included women and minorities. She performed the first cardiac ultrasound in space.
Before the space program, Seddon told the students, many predicted dire consequences for human beings living in zero gravity. It wasn't clear whether humans would be able to even swallow and keep from choking on their own saliva.
Early space flights proved that humanity could, in fact, live and function in zero gravity, but much more needed to be tested and confirmed, and the 1991 mission highlighted by Seddon did pioneering research on life without most of Earth's gravitational pull. It paved the way for astronauts to spend longer terms in space aboard the International Space Station.
It took two years of training to become a shuttle astronaut, and the training for a specific mission was normally a year. In the case of STS-40, the complexity of the scientific mission required two years of training -- but delays extended that time even further, and Seddon spent seven years training for the mission, her second flight aboard the shuttle.
Everything begins with the launch, and Seddon pointed out that the solid rocket boosters that put the shuttle into orbit burned for two minutes, "whether you want them to or not." Unlike the liquid-fueled rockets, which launched previous manned missions, they cannot be shut down. The shuttle is traveling at 100 miles per hour by the time it clears the launch tower.
Once in orbit, the shuttle travels around the earth every 90 minutes. Shuttle astronauts could look at the California coast, and then nine minutes later at Chesapeake Bay. They were asked to photograph Kuwaiti oil field fires resulting from the first Gulf War.
At one point, they witnessed a bright streak far below them, looking towards Earth. It was a meteor entering the atmosphere.
But the medical research was the reason for the flight. Seddon said scientists had theorized that an astronaut's blood pressure would be higher than normal, because of the way fluids in the body and around the heart redistribute in zero gravity.
But tests conducted on STS-40 refuted that; blood pressure was actually lower than normal. The baroreflex, one of the body's mechanisms for regulating blood pressure, is responsible for a lowering of blood pressure when you stand up after lying down. Research revealed that the baroreflex goes away after just a few days in zero gravity, where the concepts of lying down or standing up have no real meaning.
Testing also revealed that the body has no problem moving blood from the legs back to the heart and lungs. Lung capacity decreases somewhat in zero gravity, because organs beneath the lungs, in the absence of gravity, float and put pressure on the lungs from below.
Astronauts also adapt mentally to their new environment. At the beginning of the nine-day mission, when the astronauts needed to huddle to discuss something, they tended to sit in a traditional orientation, with their feet towards the floor of the shuttle. As the mission went on, they tended to orient themselves in whatever way was convenient or comfortable, without reference to earthbound notions of "up" and "down."
The lab rats, however, weren't prepared to understand their new environment. There had been concerns about how researchers would be able to handle a lab rat in a zero-gravity environment, and whether the rat might be able to escape a researcher's grasp. STS-40 was the first time humans had directly handled animals in space; animals taken into space for previous experiments were in sealed containers, studied before launch and after landing but not handled while in space.
As the video showed, concerns about a rat getting away were unfounded. In fact, a rat, disoriented by its new environment, did everything possible to keep its grasp on the researcher handling it.
The human astronauts, on the other hand, enjoyed the novelty of the zero-G environment. During their free time, which Seddon called "recess," they flipped and tumbled. At one point, the mission commander did pushups with the entire seven-member crew riding on his back.
Eventually, of course, it was back to business. Other experiments conducted on the mission included performing stitches and CPR on mannequins, to test procedures for dealing with an in-flight medical emergency. An enclosed work bench which future shuttle missions would use for scientific experiments was tested to see if it could properly handle materials, without contaminating the rest of the cabin.
Particles and liquids in a zero-G environment tend to float around, which must be taken into account in various parts of mission planning. For example, astronauts eat tortillas instead of bread because crumbs would create an airborne mess.
The crew slept in sleeping bags with head and arm holes, without any gravity to push them down onto a mattress or pad.
For early space missions, astronauts breathed air with greatly-reduced pressure, but to which increased levels of oxygen had been added. The shuttle, by comparison, had air pressure and oxygen content similar to Earth. That meant the shuttle had to be built more sturdily to contain the higher pressure, Seddon pointed out.
Seddon took a number of questions from Webb students -- including one tongue-in-cheek question about whether she'd seen any evidence of aliens.
"That's a secret," she quipped.
Seddon is former assistant chief medical officer of Vanderbilt Medical Group; she is now a partner with Nashville-based LifeWings Partners LLC, which develops patient safety programs for hospitals. Seddon is married to another former astronaut, Robert L. "Hoot" Gibson, who flew five shuttle missions and was commander of four of them.