NASA: Capillary Cup
The Capillary Cup is a zero-gravity cup designed by NASA astronaut Donald Pettit on the International Space Station. The product is an open drinking cup designed to be used in a microgravity environment, developed from Pettit’s desire to drink water without a bag and straw in outer space.
“We take gravity for granted,” Pettit said. “Generally, we are unaware of the weight of our hands, or how easily we pour coffee into a cup. We don’t stop to think, ‘Will the coffee rise up and pour out?’ or ‘Can we pour the coffee?’ We just do it. Gravity handles this for us by applying force to the coffee, pulling downward.”
As an astronaut and someone standing right on the frontier, Pettit always keeps his eyes open for new opportunities and experimentation — or, in his own words, “just goofing around.”
The cup began as a series of cheaply equipped experiments out of Pettit’s curiosity about liquid behavior in space. The project was eventually financed and studied by NASA, with its results published in a number of papers.
“Consider what will happen when the pull of gravity goes away from the cup of coffee,” Pettit said. “From what we know about earthbound coffee drinking, there will be no gravity to pull the coffee downward as we tilt the cup. We tilt the cup, and the coffee stays level. As the cup tilts, the edge of the mug reaches the edge of the coffee and liquid simply pours out. It’s that simple.”
The first prototype, fabricated by Pettit on the International Space Station, is made of repurposed Mylar sheeting and Kapton tape. Applying the principle of capillary channel flow, he formed the cup, pinched into a teardrop shape as the fluid flows along a narrow channel to the rim for drinking.
The prototype was developed into the second version, designed by Mark Weislogel and his team at Portland State University. The cup is made out of 3D-printed food-grade plastic and has been flight-tested by NASA. The use of complex fluid dynamic geometry enhances the hydration experience that is closer to what we’re accustomed to on Earth.
Later, Pettit crafted his own handmade version of the capillary cup based on Weislogel’s design. This porcelain ceramic version is now on the International Space Station and is the first patented product invented in orbit.
It is a prime example of the intersection of design, science, and engineering. It allows crews to drink and toast from an open container commensurate like how we do on Earth.