In 2015, astronauts brewed espresso in orbit and drank it from a 3D-printed cup; surface tension pulled the coffee toward their lips without gravity

For most people, a cup of coffee is just a cup of coffee. We pour, we sip, gravity does the rest. However, on the International Space Station, even this simple act becomes an engineering challenge. According to a NASA blog post by aerospace researcher Mark Weislogel, Ph.D., on the agency's "A Lab Aloft" blog, NASA designed, built, and flight-tested a special 3D-printed cup so astronauts could finally drink coffee the normal way, lips to rim, instead of sucking it through a straw out of a sealed pouch.

The cup was used with ISSpresso, an espresso machine built in Turin, Italy by the firm Argotec in partnership with Lavazza, which launched to the space station aboard a SpaceX cargo flight in April 2015 and arrived in early May 2015, according to NASA and Italian Space Agency records. ESA astronaut Samantha Cristoforetti later used the machine and cup, and a widely circulated photo shows her sipping espresso beside the station's Cupola window.

Why coffee refuses to behave in orbit

On Earth, gravity pulls liquid downward and keeps it in a cup. In microgravity, that force is almost non-existent. Instead, liquid clings to surfaces because of surface tension, the tendency of molecules to stick together and to nearby surfaces. Tipping a regular cup in space would not spill the coffee. It just stays there, stubbornly stuck in place. This led NASA to rethink the cup design. A NASA technical brief on the invention states that astronaut Don Pettit came up with the first version of a solution while living on the station, and researchers Mark Weislogel, with mathematical consultants Paul Concus and Robert Finn, helped to refine the idea into a patented design. Their invention uses the same physics that makes water climb a thin straw or a paper towel soak up a spill, known as capillary flow.

How the space cup really works

The final version, sometimes dubbed the 'Space Cup', was 3D-printed from food-safe plastic. Researchers writing in Frontiers in Space Technologies, in a study titled 'Microfluidics and Macrofluidics in Space: ISS-Proven Fluidic Transport and Handling Concepts,' explain that the cup has a narrow, tapered interior corner from the base to the rim. That shape creates a constant capillary pressure gradient, drawing liquid along the corner to the lip without a pump or gravity. When the liquid reaches the top, the forces balance and the flow stops until the astronaut takes another sip.

The NASA blog post reports that six of these cups were already aboard the station and ready for use by the time the post was published in May 2015. The cups were part of a formal experiment called the Capillary Beverage investigation, designed to gather real data about how complex fluids flow in the absence of gravity, beyond just making coffee easier to drink.

Would space espresso even look the same

Weislogel's post also raises a fair question: would the espresso even develop the crema, that thin layer of foam on top of a well-made shot? Unlike the coffee itself, which stays in continuous contact with the cup's corner as capillary action pulls it along, the tiny bubbles that form crema need buoyancy to separate and coalesce into a stable foam layer, a force that's minimal in microgravity. The blog says this makes crema unlikely, so the coffee might look different even if it tastes the same.

Why this matters beyond the coffee cup

Weislogel's post says the data from the Space Cup experiment was fed into math models that help engineers design how liquids move inside containers. Two practical applications stand out: completely emptying rocket fuel tanks, since any fuel left over is wasted weight and money, and delivering accurate doses of medication where the exact amount is crucial. WIRED magazine later named the design one of the most cleverly designed objects of 2015.

It’s easy to read as some fun piece of space trivia and move on, but it's actually a neat case of simple physics quietly solving a real problem. Astronauts wanted coffee that behaved more like it does at home, and that goal drove the engineering work. Next time you take a sip of coffee, remember that scientists had to study surface tension to make it possible in space.