``Capillary Cup'' is a special cup designed for use in a microgravity environment, developed from the desire to ``drink coffee from a cup even in space.''

The International Space Station (ISS), which flies approximately 400 km above the ground, has a microgravity environment, and the behavior of various objects differs from that on the ground. ' Capillary Cup ' is a special cup developed to fulfill the wishes of astronauts to drink water without using bags or straws in a microgravity environment.

NASA: Capillary Cup | Vignelli Center | RIT
https://www.rit.edu/vignellicenter/product-timecapsule/nasa-capillary-cup

' Surface tension ' acts on the surface of liquids, not just water, which tries to minimize the surface area as much as possible. Therefore, as you can see in the movie below, when you put water inside the ISS, it becomes spherical in the air.

4K Video of Colorful Liquid in Space - YouTube


Additionally, because water has a strong surface tension, when it comes into contact with water in a microgravity environment, it sticks to the skin and does not let go. In the YouTube short below, you can see a spilled drink from a plastic bottle stick to a crew member's face, and then he finally tries to blot it up with a towel.

NASA water bubble - YouTube


For these reasons, the act of ``pouring liquid into a mug and drinking it,'' which is commonplace on land, becomes impossible in a microgravity environment. On the ISS, you will need to use a special container or straw to drink water. The phenomenon of ``coffee flowing into your mouth when you tilt the cup'' can only occur because gravity exists as firmly as it does on earth.

The Capillary Cup was developed by Donald Petty , a NASA astronaut, thinking, ``Is it possible to develop a cup that allows you to drink water or coffee directly like on the ground even in the microgravity environment of the ISS?'' The first prototype made at the ISS was made of water-resistant sheet and tape, and was designed to apply capillary action , where liquid moves through narrow gaps, to allow liquid to flow all the way to the edge of the spout.

You can see how Mr. Petty actually drinks coffee with this prototype version of Capillary Cup from around 46 seconds of the movie below.

ISS: Science in a Cup - YouTube


This prototype was later refined in collaboration with Mark Weislogel of Portland State University. The cup is designed to be printed using a 3D printer and is made of plastic that can be used for meals. By applying fluid dynamics, it seems that you can drink water and coffee in a way similar to what you would do on land.

In addition, Mr. Petty developed a ceramic version of the Capillary Cup, which he co-designed with Mr. Weislogel. This ceramic Capillary Cup is a fixture of the ISS at the time of article creation, and is the first product invented at the ISS to receive a patent.