NASA Cassini image of the swirling clouds on Saturn

Nature is an artist, and this time she seems to have let her paints swirl together a bit.

What the viewer might perceive to be Saturn's surface is really just the tops of its uppermost cloud layers.

Everything we see is the result of fluid dynamics.

Astronomers study Saturn's cloud dynamics in part to test and improve our understanding of fluid flows.

Hopefully, what we learn will be useful for understanding our own atmosphere and that of other planetary bodies.

This view looks toward the sunlit side of the rings from about 25 degrees above the ringplane.

The image was taken in red light with the NAC (Narrow Angle Camera) Cassini spacecraft on Aug. 23, 2014.

The view was acquired at a distance of approximately 1.1 million miles (1.8 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 127 degrees. Image scale is 7 miles (11 kilometers) per pixel.

ISS: Keeping Rocket Engine Fuel Lines Bubble Free in Space

Astronaut Scott Kelley installing the Capillary Channel Flow, or CCF, in the Microgravity Science Glovebox, or MSG, on board the International Space Station. 

Photo Credit NASA.

Without gravity in the space environment, how do you keep the fuel contained so it can be transported to where it is needed? How do you keep gas bubbles out of the fuel lines?

Being able to use all of the fuel in a spacecraft tank has been an ongoing challenge in spacecraft design for the past 50 years, but great advances on the problem are being made using the International Space Station as a laboratory. In the microgravity of space, the "bottom" of the tank is NOT apparent.

When a spacecraft tank is nearly full, the fuel tends to "cling" to all sides of the tank leaving a small gas bubble, or ullage, near the center of the tank. Once the tank has emptied to the point where there is not enough liquid to cover the walls of the tank, it is not clear where the remaining fluid is "positioned."

Here on Earth this is not an issue. For example, in the gasoline tank in your car, gravity always positions the remaining fluid at the bottom of the tank, allowing the car's fuel pump to draw the last bit of fuel from the tank.

"Presently, the low risk solution to this problem is to size the fuel tank larger than what is needed for the mission, but this adds extra launch mass and volume to the spacecraft," states Robert Green at NASA's Glenn Research Center.

Another method is to add special channel-like structures, called vanes, inside the tank to purposely "wick" the remaining fuel to the exit. A key area of study is how different shapes of channels work and whether they remove any gas bubbles that can get captured in the flow.

ESA scientists from Germany and the U.S. have been studying these processes as part of an investigation called Capillary Channel Flow, or CCF. The CCF study looks at several capillary channel geometries that mimic the shape and physical characteristics of vanes in fuel tanks.

One set of capillary channel geometries was developed by Michael E. Dreyer at the Center of Applied Space Technology and Microgravity, or ZARM, at the University of Bremen in Bremen, Germany, and sponsored by the German Aerospace Center, or DLR.

The geometries included parallel plates and square-grooves. This part of the investigation was completed in March 2011, after 78 days of nearly continuous ground-controlled operation.

The second set of channel geometries was designed by Mark M. Weislogel at Portland State University in Portland, Ore. Sponsored by NASA, it will begin operation this month. The geometry is a wedge-shaped channel with only one side exposed to the interior of the tank. Weislogel is studying the fluid behaviour in the interior corner where the two plates meet.

Jellyfish; The Spoons of the Sea

When to the new eyes of thee
All things by immortal power,
Near or far,
Hiddenly
To each other linked are,
So that thou canst not stir a flower
Without troubling a star...........

(Francis Thompson)

NEXT time you go for a dip in the sea, bear in mind that your deft front crawl is helping to mix up the waters. In fact, marine life may be stirring the oceans and moving nutrients around as much as winds or tides.

According to a theory proposed by Darwin's grandson, Charles Galton Darwin, a body moving through water drags some of the fluid with it.

Darwin's Drift

In "Darwin drift", a high-pressure zone forms at the front of each swimming animal, leaving an area of lower pressure behind, which draws in adjacent water. This results in a net movement of fluid in the direction of the swimmer.

Swarms of Jellyfish

To test the idea, Kakani Katija and John Dabiri at the California Institute of Technology in Pasadena went to a lake in the Republic of Palau in the Pacific Ocean. Diving among swarms of jellyfish, the pair used suspended dyes and a newly designed laser velocimeter to measure the movement of water around the jellyfish. They found that the animals did indeed drag water with them as they swam (Nature, vol 460, p 624).

Mixing Energy

The researchers then estimated the total energy that all ocean swimmers impart on the water. They calculated that it was on a par with the mixing energy imparted by winds or tides. The findings suggest ocean swimmers can move water over long distances and that they could help run the vertical currents that push nutrients around between the sea floor and surface waters.