Five of the space cups can hold 150 milliliters, and the sixth is a 60 ml half-cup that is supposed to work with the station's new espresso machine. The cup is "complexly designed" but stems from 2013 research where part of the cup had a very sharp inside corner, forcing fluids through that channel and to your mouth.
ANALYSIS: Coffee Machine Heading to Space Station
"Wetting conditions and the cup's special geometry create a capillary pressure gradient that drives the liquid forward toward the face of the drinker," said team member Mark Weislogel in a statement. Weislogel is a senior scientist for Oregon-based fluid engineering firm IRPI LLC, and a mechanical engineer professor at Portland State University.
"Your nose is closer to the beverage, which makes it easier to actually smell it while drinking," he added. "An astronaut can drain the cup in sips or one long gulp in much the same manner as on Earth ... without tipping their head, without gravity. It's a stable situation - even though drinking scalding liquids from open containers while aboard the International Space Station is generally considered a safety concern."