July 15, 2013: High above our planet in the realm of satellites and space stations, the familiar rules of earth do not apply. the midday sky is as black as night. there is no up or down. dropped objects do not fall and hot air does not rise.
Of all the weird things that happen up there, though, it’s just possible that the weirdest thing happens to coffee.
Reading: Zero gravity coffee cup
Physics professor Mark Weislogel of Portland State University has thought a lot about coffee (and other fluids) in space, and he describes what happens:
“For starters,” he says, “it would be a chore to just place the coffee in the cup. Without the pull of gravity, pouring liquids can be very tricky.”
“but for the sake of discussion, let’s say you’re on the space station and you have a cup of coffee in your hand.” The most natural thing would be to tilt the glass towards your lips, but when you do…
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“Coffee would be very difficult to control,” he continues. “In fact, it probably wouldn’t [come out of the cup]. You’d have to shake the cup towards your face and hope that some of the hot liquid would break free and float up to your mouth.”
On the plus side, you’ll probably be wide awake when the cup is empty.
Coffee is not the only liquid that misbehaves in space. cryogenic fuels, thermal coolants, drinking water and urine do too. fluid behavior is one of the most unintuitive things in all of spaceflight.
This poses an extreme challenge for engineers designing fluid-using spacecraft systems. “Our intuition is completely wrong,” laments Weislogel. “When it comes to guessing what fluids will do in new systems, we often don’t know anything.”
To develop a better understanding of fluids in microgravity, Weislogel and colleagues are conducting the Capillary Flow Experiment aboard the International Space Station. for example, one of the devices in your set of experiments looks at “inner corners”. if two solid surfaces meet at a narrow enough angle, fluids in microgravity flow naturally along the junction, without the need for pumping. this capillary effect could be used to guide all kinds of fluids through the spacecraft, from cryogenic fuel to recycled sewage. The phenomenon is difficult to study on Earth, where it is dampened by gravity, however, on the space station, large-scale corner flows are easy to create and observe.
weislogel and his colleagues have already obtained three patents for devices invented as a result of their work. one is for a microgravity condensing heat exchanger. another describes a device that separates and controls multiphase fluids. the third patent is for, you guessed it, a low-gravity cup of coffee.
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astronaut don pettit, who worked on the capillary flow experiment during his time aboard the iss, helped invent the cup and shares the patent with weisogel and two mathematicians, paul concus and robert finns, who performed the first theory analysis of the phenomenon.
Basically, one side of the mug has a sharp inside corner. in the microgravity environment of the space station, capillary forces send the fluid flowing along the channel directly to the lips of the drinker.
“as you drink, more liquid keeps coming out and you can enjoy your coffee in a weightless environment, clean to the last drop”, says pettit. “This may well be what future space colonists wear when they want to have a celebration.” in fact, the patent application specifically mentions “toasting” as one of the uses of the device.
It’s easy to imagine what they might be providing: toilets, air conditioners, fuel tanks, and recycling systems, all made better by capillary flow experiments on the ISS.
credits:
author: dr. Tony Phillips | production editor: dr. Tony Phillips | credit: science@nasa
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