Science off the Sphere (Science off the Sphere) - 07.14.16
Science off the Sphere is a collaborative effort between Astronaut Dr. Don Pettit and the American Physical Society demonstrating unique physical properties that occur on the International Space Station. Science Results for Everyone
Donald Roy Pettit, Ph.D., Johnson Space Center, Houston, TX, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
September 2011 - September 2012
- Science off the Sphere is a collection of physics demonstrations designed for students of all ages to understand.
- Science off the Sphere inspires and educates the next generation of scientists and explorers by demonstrating the unique properties of fluids and materials in microgravity.
Astronaut and chemical engineer, Dr. Don Pettit, demonstrates unique physical phenomena that occur in microgravity during his free time on the international Space Station. The videos are downlinked and posted to the Science off the Sphere website (http://www.physicscentral.com/explore/sots/). At the end of each video Dr. Pettit poses a challenge question. A winner is chosen randomly from all correct answers submitted. The winner's name is read from space and they receive a snazzy t-shirt from Earth. The following videos are found at the Science off the Sphere website:
Episode 1: Dancing Droplets
Dr. Pettit explores static electric forces using knitting needles, a syringe, and water.
Challenge Question: In the end of the video, Dr. Pettit put a nylon knitting needle near the syringe used to squirt water droplets onto the Teflon knitting needle. Why did Dr. Pettit need a nylon needle near the injected drops and why must the other needle be Teflon?
Challenge Answer: Teflon acquires electrons from other materials when rubbed, thus attaining a negative charge. Nylon gives up electrons to other materials when rubbed becoming positively charged. When the droplets come out of the syringe near the positively charged nylon needle they give up some electrons to it becoming positive themselves. This makes the water droplets more attracted to the negatively charged Teflon needle because dissimilar charges attract.
Episode 2: Bistro-nauts
Dr. Pettit and fellow crewmates take a tea break and have a crew toast while examining capillary forces in the absence of gravity.
Challenge Question:Why can't you use a regular cup in microgravity?
Challenge Answer: Using a regular glass, water particles are attracted to the bottom, and sides of the cup. A small disturbance, such as taking a sip, would cause the liquid to separate from the glass. If the surface tension did not hold the water together, water would float around everywhere. With the "Space-Cup", the liquid will stay attached to the edges, and capillary action will keep the water connected when taking a drink.
Episode 3: Thin Film Physics
Dr. Pettit investigates the behavior of water as a thin film in microgravity and Marangoni convection utilizing a metal ring, water, and a soldering iron.
Challenge Question:Why does the shape of the water sheet affect the direction of the Marangoni convection?
Challenge Answer:Heat weakens surface tension, so water gets pulled away from the heat source. But to maintain the film, water has to replace it (or it breaks like at the end). So should the water move away along the edges, to be replaced by water from the center, or should it be the other way around? Water heats faster where it is thinner, so there's a preference to move away from the heat along the thinner water path. In the convex case, that's along the edge. In the concave case, that's toward the center.
Episode 4: Lenses and Vortices
Dr. Pettit makes interesting observations about water sheets using different geometries, loops, and experiments.
Challenge Question: How does the viscosity of the fluid influence a vortex?
Challenge Answer: Higher the viscosity, lesser the vortex, as more viscous fluid is, greater is the molecular attraction, that`s why honey will have less vortex producing capacity than water.
Episode 5: Fun with Antibubbles
In this episode, Dr. Pettit plays with the properties of bubbles injected within rotating bubbles.
Challenge Question: When the water sphere rotates, why do the bubbles center themselves?
Challenge Answer: When gravity is taken out of the equation, I can only see another force that acts on the bubbles: the centrifugal force. Water is denser than air so it is pushed to the outside of the bubble as it feels a greater centrifugal force (but water also has strong intermolecular forces so it doesn`t scatter) and air is accumulated in the middle (as the other space is taken by the water).
Episode 6: Earth in Infrared
Dr. Pettit demonstrates how earth observation scientists use cameras with the infrared blocking filter removed to investigate the health of agricultural crops.
Challenge Question: Why do plants appear red in infrared pictures and cities grey?
Challenge Answer: Plants reflect IR light. This picture was probably taken during the day, so the plants are reflecting IR, while the concrete cities are absorbing it. At night, the cities will be visible as they release heat in the IR spectrum, while the plants will be dark.
Episode 7: Space Soundwaves
Dr. Pettit uses laptop speakers, music from his mp3 player, and water to observe how the frequency and amplitude cause various sizes of water drops to behave differently.
Challenge Question: Why does Don use low frequencies to get the water to jiggle?
Challenge Answer: We think it is because the lower frequency vibrations allow for the formation of standing waves. Standing waves are made when two waves traveling in opposite directions intercept allow them to have constructive and destructive interference. This is more likely to happen at lower frequencies.
Episode 8: Goo!
Dr. Pettit uses laptop speakers, music from his mp3 player, cornstarch, chopstick, and water to demonstrate how a non-Newtonian fluid (the cornstarch and water mixture) behaves in microgravity.
Challenge Question: Don's cornstarch solution is a shear-thickening non-Newtonian fluid. What would change if Don used a shear-thinning fluid such as ketchup?
Challenge Answer: The shear-thinning fluid would tend to spread out when disturbed instead of mound up. At the edges of the speaker, the shear thinning liquid would tend to pile up where the oscillations stop and mound up into a ring.
Science off the Sphere demonstrations provide insight into how fluids and materials behave differently in microgravity compared to gravity on Earth.
The simple demonstrations using everyday materials for Science off the Sphere play a major role in inspiring the next generation of scientists, engineers, and explorers.
Operational Requirements and Protocols
All protocols designed and carried out by Don Pettit.
Decadal Survey Recommendations
Information Pending^ back to top
Fontana P, Pettit DR, Cristoferetti S. Sodium chloride crystallization from thin liquid sheets, thick layers, and sessile drops in microgravity. Journal of Crystal Growth. 2015 October 15; 428: 80-85. DOI: 10.1016/j.jcrysgro.2015.07.026.
Fontana P, Schefer J, Pettit DR. Characterization of sodium chloride crystals grown in microgravity. Journal of Crystal Growth. 2011 June; 324(1): 207-211. DOI: 10.1016/j.jcrysgro.2011.04.001.
Ground Based Results Publications
Chand SP. Effect of Centrifugal Force on the Characteristic Orientations in Antibubbles under Microgravity Environmental Conditions. International Journal of Applied Engineering Research. 2014; 9(11): 1315–1324.