Space travel is a bit more civilized now that there's a bespoke Italian espresso machine aboard the International Space Station (ISS). Unfortunately, solving one problem just raises another and the astronauts are still having to drink their cappuccinos out of placcy bags. To help the zero-g coffee aficionado, Portland State University's (PSU) Maseeh College of Engineering and Computer Science has developed a microgravity espresso cup that drinks like its earthbound counterparts.
Fluids don't act the same in space as they do on Earth. With no gravity to overcome surface tension, they form globules and stick to containers like jelly, so a cup of coffee becomes a hot mug of frustration. This is why astronauts have relied on plastic bags and squeeze bottles for drinking. PSU's reasoning is that if there isn't any gravity to help the coffee flow, then use some other natural force to do the job.
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The new cup is not the first such produced by PSU, but it is the next step in the process of creating a practical zero-gravity drinking vessel. Designed by professor of engineering Mark Weislogel, PhD student Drew Wollman, PSU alumnus Ryan Jenson, and NASA astronaut Don Petitt, the patented cup is 3D-printed by start-up IRPI LLC and looks like an oddly shaped pitcher with an elongated lip. This forms a thin channel with a specially-calculated contour that uses capillary pressure to force liquid out of the cup and up to the lip in a manner similar to pouring.
The reason why it's an espresso cup is that by simulating the forces found on Earth, it helps in producing the "crema" of an espresso, which involves the proper separation under gravity of the complex mixture of low-density colloid of emulsified oils. The capillary pressure is not a perfect substitute, but it is an improvement.
"Its geometry is the 'smart' part, which provides the fluids-control system without requiring pumps or centrifugal forces," says Weislogel. "The shape of the container can passively drive fluids to desired locations without moving parts – exploiting the passive forces of wetting and surface tension."
The zero-gravity espresso cup may seem like a superfluous bit of galley kit, but there's some serious business behind it. What affects a macchiato also affects spacecraft. The Venus Express mission, for example, ended, in part, because what little fuel remained in its tanks was probably stuck in blobs too far from the engine intakes to do any good. The same goes for fluids in everything from rocket engines to life support systems to toilets, so NASA is conducting a series of experiments on the ISS called Capillary Channel Flow (CCF) and Capillary Channel Flow Experiments-2 (CFE-2).
PSU is involved in this effort to produce new computer models and analytical tools for figuring out how fluids will act in zero gravity. As part of this, the zero-gravity espresso cup will be used as part of NASA's Capillary Beverage Experiment. PSU says that six of the cups will be sent to the ISS in February on a SpaceX Dragon resupply mission. Once there, the cups will be used to not only drink coffee, but also to see how well they work with complicated drinks, such as cocoa, peach mango smoothies, and clear juices. The cup made its public début at the American Physical Society's Division of Fluid Dynamics Meeting in November.
The NASA video below discusses the space espresso cup and the ISS experiments.