"Over the top!"
The call through the airplane alerts passengers that the aircraft has reached the zenith of its parabolic flight-path and is about to nose over into a roughly 8,000-foot dive.
Suddenly, the interior of the aircraft is transformed into a surreal world: girls' hair hangs suspended in midair, shoelaces hover over their accompanying shoes, an unfastened duffel bag rises into the air and floats above the seats like magic.
It isn't magic. It's NASA's zero-gravity aircraft, and the passengers are members of 14 student teams from universities across the nation whose research proposals were selected for NASA's Reduced Gravity Student Flight Opportunities Program.
Jokingly described by program coordinators as the world's fastest weight-loss program, the grant awards undergraduates the inimitable opportunity to propose, design, fabricate and test a research project in zero gravity.
Two teams from the University of Arizona were selected this year and completed tests on their experiments last week at Ellington airfield in Houston.
The program gave students a chance to participate in a very real world of science and engineering research well beyond the classroom. At Ellington airfield, the teams were given three days and a weekend to finalize their experimental setups before flight, immersed in a professional science and engineering environment where safety and professionalism are counted top priorities.
The teams worked on tables and workbenches in an open hangar, in the shadow of a looming 727 airplane.
Before loading their experiments onto the zero-gravity aircraft, the set-ups had to pass the Test Readiness Review, or TRR, in which team members presented their projects to a group of NASA officials and explained every phase and function of the experimental setup. Once the officials were satisfied that the experiments were test-ready and safe, the setups could be loaded onto the plane.
A robotic arm, parasitic nematodes and a mechanical model of a human torso with a simulated circulatory system were among the projects that found a home bolted to the floor of the aircraft.
How will a lens created by the interface of immersion oil and water work in microgravity, where the only force acting on it is the comparative density of the two liquids? That was the question asked by the team from the UA's chapter of Students for the Exploration and Development of Space, or SEDS.
Liquid lenses don't work well on large scales in Earth's gravity because the force disrupts the curvature of the liquid interface. But in a weightless environment, the pressure of the liquids on each other could be altered to generate variance in the curve of the interface, without gravity to disrupt the curvature, creating an adjustable lens that would work even on large scales.
The SEDS team built liquid lenses out of immersion oil and water encased in an acrylic cube and tested the construct in zero gravity by imaging computer-generated vertical and horizontal lines through the lens.
"We were looking for symmetry," said Kyle Stephens, the leader of the UA SEDS team. If the lines appeared symmetrical, it would indicate that the lens worked well.
"We definitely saw some difference to how the lens performed on Earth, but it wasn't the symmetry we were expecting."
Even a small difference in the lens's function between Earth and microgravity is still enough to indicate that liquid lenses might be a viable option in zero-g environments.
If they could do it again, said Stephens: "We would definitely want to look more into the fluids that we used and see how they interacted with each other and with the container and decide what fluids would be best in that environment. We chose the fluids based on how light travels through them and how they interact with each other optically."
Stephens said the team probably would look more into the material properties of the liquids, such as their viscosity and how that affects the shape of the liquid interface.
"The fluids we had were resisting movement once we hit zero-g," said Stephens. "And we want fluids that would hit that perfect shape."
While one UA team tested fluid interactions, the other combined gases in sealed chamber in the presence of water vapor and sparks generated by a spark coil.
Known as the Miller experiment, this test originally was done in 1953, and resulted in the production of organic compounds such as amino acids, the building blocks of DNA. It is thought to have demonstrated the process by which life first formed on the early Earth.
Now, some comets and asteroids have been shown to have organic compounds as well, and it is hypothesized that the compounds may have formed via this same process. One UA team is testing that hypothesis, reproducing the Miller experiment in zero gravity to see if gravitational fluctuations, such as would be experienced by a comet or asteroid traveling through space, have any effect on the formulation of organic products.
"We are hoping to see the 20 common amino acids," said Alex Stanton, a member of the team that reproduced the Miller experiment. "But we expect to see many other smaller organic compounds, with amino acids probably in the minority. The original experiments did create other amino acids not found on Earth, and this is not unexpected for our experiment, but it is more unlikely because we used the ‘traditional' setup for this experiment. There are two other setups, and these give higher concentrations of the non-Earth amino acids."
"By qualitative observation of the product and the residue within the apparatus, we believe we can say that organic products were formed," said Stanton. Results of the experiments await analysis following their trials in zero gravity.
Unlike on roller coasters where the fun is to experience the force of acceleration, the pilots of NASA's zero-g aircraft try to maneuver the plane along the perfect curve of the parabola so that the passengers hardly feel the transition into zero gravity – they just lift off the floor.
Everything inside the airplane, including the passengers, hangs in the air.
"It is perhaps one of the most startling and unexpected things that has ever happened to me," said Stanton of experiencing weightlessness.
The experience is extremely disorienting, because the body's sensory organs responsible for detecting the direction and intensity of gravitational forces are disrupted by the conflicting signals of falling while the surroundings seem perfectly still.
The freefall lasts between 20 and 30 seconds as the plane drops from roughly 24,000 feet in elevation to about 16,000 feet.
Then: "Feet down!"
The signal for the end of the zero-g portion of the parabola gives the experimenters just enough time to recall that for all intents and purposes "down" is the side of the plane to which their experimental setups are attached, before the plane turns up again and begins to climb at an angle between 30 and 45 degrees. The greatest angle most commercial airlines ever achieve is much smaller.
The plane climbs with a force nearly equal to two g's, or twice the gravitational force on Earth. A person weighing 100 pounds will feel as though they weigh 200 pounds.
"I especially enjoyed the transition between two g and zero g, because I would be flat on my back and feel as if a magnet was holding me in place. Then I'd be halfway to the ceiling before I could catch myself."
"It was pretty much like nothing I've ever experienced," said Stephens. "It was very strange looking down the plane. You looked up but it felt down, or you looked down but it felt up."
Now back on Earth, the teams will wrap up their research with several outreach events, such as presenting their projects at schools and educating people about their experiments to encourage public engagement in science.
Primary funding for the UA teams' research came from NASA's Reduced Gravity Student Flight Opportunities Program and from NASA Space Grant. The UA SEDS team received additional support from the LOFT group at the UA, and from its faculty advisor, Roger Angel. The UA team reproducing the Miller experiment received support from its faculty supervisor, John Pollard; from the Betterton lab and from the Hall lab; and from the department of chemistry and the departments of physics and atmospheric sciences at the UA.
This feature is the third in a three-part series on UA students' involvement in zero-gravity experiments. The first article: UA Teams Selected for Zero-Gravity Flights. The second article: Experimenting in a Weightless Laboratory.