One of the teams selected for NASA's Microgravity University project chose to revisit a microgravity demonstration done more than 30 years ago on the first U.S. space station, Skylab.
The team from the University of Colorado at Boulder chose to experiment with a Wilberforce Pendulum, a device that was demonstrated on Skylab in 1973.
A Wilberforce Pendulum is a spring/mass system in which, when compressed and released, the mass both bounces and spins. The mass experiences both linear and angular oscillation. After a few seconds, it stops bouncing and is only spinning. After another few seconds, it stops spinning and is only bouncing. The system demonstrates the physics behind basic coupled modes.
On Skylab, several factors caused the demonstration not to work as expected. The spring buckled, and the astronauts were not able to observe the coupled modes.
The Colorado students sought to improve the Skylab demonstration by limiting the spring's movement. The spring was threaded onto a steel wire that was mounted to a box frame. This design was intended to constrain the motion of the bending moment and allow the lateral motion transfer to rotational motion.
The team tested their theory by flying two Wilberforce Pendulums -- a one-mass system and a two-mass system similar to the one used on Skylab -- on a reduced-gravity aircraft as part of Microgravity University. The project is part of the Reduced Gravity Flight Program at NASA's Johnson Space Center in Houston, Texas. It offers undergraduate students the opportunity to propose, design, fabricate, fly and evaluate a reduced-gravity experiment. The project supports NASA's goal of strengthening the agency's and the nation's future workforce.
Colorado team lead Kristian Hahn said the team expected to see both spring/mass systems exhibit the coupled mode and to observe the transition of momentum from linear to rotational. "(In the single-mass system) the coupled mode was very clear, and the transitions seemed to go very smoothly," Hahn said. "However, for the free-ended system the bending moment and friction made it very difficult to see any transition of momentum from one mode to the other."
Junior aerospace student Swarandeep Singh said the team expected friction to be an issue but tried to mitigate it in the design. "I knew friction would play a large part in the quality of the experiment, but there was no real way to test the spring systems in a microgravity-like environment prior to the flight," Singh said. "We knew the friction in the springs would be detrimental, but I was surprised to see how fast the double-mass system dampened."
If they were to fly their experiment again, team members have ideas for how they would do things differently. Singh has suggested using stronger springs and a lubricant to prevent friction between the springs and the wires. "Stronger springs mean there is more energy in the system and frictional effects may be small depending on the size of the masses," Singh explained.
Senior aerospace student Karina Ogilvie suggested experimenting with different methods of attaching the masses to the springs to find a more symmetric way of mounting the springs. Christopher Chavez Jr., the mechanical engineering student on the project, envisioned constraining the springs in a tube and using compressed air to guide the spring/mass systems.
While the two-mass system did not perform quite as expected, the team is using the experience to teach younger students about physics and hopefully encourage them to be interested in science, engineering and NASA. Prior to their flight, Colorado students gave a series of lectures for high school and middle school students on the basic physics of coupled modes. "For the students, it was a day out of the ordinary, and for us it was an opportunity to share our experiences and promote science and engineering," Ogilvie said.
Postflight, the team created an educational video to be used with middle and high school students. The video presents basic physics concepts related to the experiment, such as conservation of momentum and energy and oscillatory physics. "We are hoping it will promote students in K-12 to become more interested in becoming part of the industry of engineering," Chavez said.
Singh would like to make the video available for college courses also, as a demonstration of modal physics. "We hear how different systems can transition from one mode to the next, but seldom do we get to see it firsthand," he said.
Experiencing reduced-gravity was a first for all members of the Colorado team. "My mind couldn't comprehend it at first," Hahn said. "With time I adjusted to the amount of actual effort needed to move my body around and was able to conduct several data collections as well as various outreach activities. I can still look back to that moment -- when I looked down and saw the ground and my entire body floating like Superman above it and then lifting my head up and seeing the ceiling above me with nothing connected to me. I was just there: I wasn't going up, I wasn't going down, just there."
Chavez said there is nothing on Earth to which it compares. "From the moment my feet left the ground, it was a feeling that no roller coaster ride could ever provide. It was one of the greatest things I have experienced in my life, and I will always remember it."
Singh said people have asked him if the feeling of microgravity is like floating in a swimming pool. "I think it is, and it isn’t," he said. "It is because that is the only thing I can almost relate it to as far as everyday experiences. But really it’s not; it is a lot more fun. It felt like all the muscles in your body are relaxed.
"You feel almost super-human because a tap of your finger will move your whole body, but at the same time you can feel very vulnerable because if you want to move away from something and there is nothing to hold on to, there is nothing you can do. I felt like I got the hang of it, but I wanted to experience it more."
Teams interested in submitting a proposal for the 2009-10 Microgravity University should submit letters of intent by Sept.16, 2009. Proposals are due Oct. 28, 2009.
Microgravity University →
Skylab Science Demonstrations: Mechanics →
Free Falling Blog →
NASA's Johnson Space Center
Heather R. Smith/NASA Educational Technology Services