【Uschi Karnat】

Astronauts may have Uschi Karnatfun drinking beverages like Pac-Man gobbles snack pellets: releasing some droplets out of a bag then swallowing them up before they float away.

But it's not too efficient. The conventional method — putting a straw in a specially sealed pouch Capri Sun-style — isn't the most enjoyable way of quenching one's thirst, either.

Over the past few years, NASA has been working on a space cup that keeps liquid in its place, even with an open top. The technology is improving life for astronauts living in the weightless environment aboard the International Space Station while giving scientists new insights into how to design other plumbing systems in space.

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A recent demo by astronaut Nicole Mann may look like magic, but the cup is leveraging the properties of fluid dynamics to mimic gravity. In the video below, posted to Twitter on March 2, Mann pipes a cappuccino into the special vessel, then gives it a gentle spin to show how the hot drink stays within the cup, even as it flips over.

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Scientists working on the device as part of the Capillary Flow Experiment say the cup functions similar to those on Earth by harnessing the combined effects of surface tension, so-called "wetting" conditions, and cup geometry. Wetting is the term for how a liquid maintains contact with a solid surface when they're brought together.

The cup has at least one channel running from bottom to rim. Capillary action between the drink and the wall of the cup allows the beverage to creep along the channel and be close to the rim. Only a small amount of the drink goes into the channel while the rest of the liquid stays at the bottom through capillary forces, according to a paper published in Nature Microgravitylast year.

When astronauts put their lips against it, the liquid spontaneously gets drawn into their mouths. They can then control how big of a gulp they receive by changing their mouth shape and suction.

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Space cups can hold liquids without a lid in microgravity through capillary action. Credit: NASA

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Capillary action happens because water is sort of sticky, meaning its molecules like to stay together. It's the same phenomenon that allows plants and trees to draw water up from their roots and a paper towel dipped in water can draw the wetness upward, seemingly defying gravity's pull.

Astronaut Don Pettit helped invent the cup during his tenure on the space station. He shares the patent, granted in 2011, with physicist Mark Weislogel and two mathematicians, Paul Concus and Robert Finns.

Various rounds of experiments have led to astronauts drinking bubble-free water, limeade, fruit punch, cocoa, coffee, and peach-mango smoothie out of the space cups. One impromptu moment led to Italian astronaut Samantha Cristoforetti, shown at the top of this story, taking her space cup full of espresso into the space station cupola.

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Astronaut Kjell Lindgren prepares to drink from a space cup. Credit: NASA

That didn't go over so well in Houston.

"For safety and design engineers on the ground, this event was met with initial alarm giving way to muted appreciation. A scalding drink (espresso) was consumed from an open container (Space Cup) in a 'clean' spacecraft environment (ISS cupola) — a triple violation," the authors wrote in the paper. "But the nature of the 'plumbing' solution of the cup was earth-like enough as to pass with limited concern."

Experiments with the cup have involved intentionally spilling drinks, which astronauts found were easier to contain than similar spills on Earth. You heard that right: It's safer to drink coffee next to a computer in space than on the ground, according to these researchers.

Astronauts say the project has improved the imbibing experience, allowing them to smell their drink as they sip, which can dramatically influence how it tastes.