Watching water droplets merge on the International Space Station

Understanding how water droplets spread and coalesce is essential for scenarios in everyday life, such as raindrops falling off cars, planes, and roofs, and for applications in energy generation, aerospace engineering, and microscale cell adhesion. However, these phenomena are difficult to model and challenging to observe experimentally.

In Physics of Fluids, by AIP Publishing, researchers from Cornell University and Clemson University designed and analyzed droplet experiments that were done on the International Space Station.

Droplets usually appear as small spherical caps of water because their surface tension exceeds gravity.

“If the drops get much larger, they begin to lose their spherical shape, and gravity squishes them into something more like puddles,” said author Josh McCraney of Cornell University. “If we want to analyze drops on Earth, we need to do it at a very small scale.”

Droplets (on the centimeter scale) merge during an experiment on the International Space Station./CREDIT:Josh McCraney

Droplets (on the centimeter scale) merge during an experiment on the International Space Station./CREDIT:Josh McCraney

But at small scales, droplets dynamics are too fast to observe. Hence, the ISS. The lower gravity in space means the team could investigate larger droplets, moving from a couple millimeters in diameter to 10 times that length.

The researchers sent four different surfaces with various roughness properties to the ISS, where they were mounted to a lab table. Cameras recorded the droplets as they spread and merged.

“NASA astronauts Kathleen Rubins and Michael Hopkins would deposit a single drop of desired size at a central location on the surface. This drop is near, but not touching, a small porthole pre-drilled into the surface,” said McCraney. “The astronaut then injected water through the porthole, which collects and essentially grows an adjacent drop. Injection continues until the two drops touch, at which point they coalesce.”

NASA/Photo: Nasa.gov

The experiments aimed to test the Davis-Hocking model, a simple way to simulate droplets. If a droplet of water sits on a surface, part of it touches the air and creates an interface, while the section in contact with the surface forms an edge or contact line. The Davis-Hocking model describes the equation for the contact line. The experimental results confirmed and expanded the parameter space of the Davis-Hocking model.

As the original principal investigator of the project, the late professor Paul Steen of Cornell University had written grants, traveled to collaborators worldwide, trained doctoral students, and meticulously analyzed related terrestrial studies, all with the desire to see his work successfully conducted aboard the ISS. Tragically, Steen died only months before his experiments launched.

“While it’s tragic he isn’t here to see the results, we hope this work makes him and his family proud,” said McCraney.

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NASA’s Swift, Fermi missions detect exceptional cosmic blast

Astronomers around the world are captivated by an unusually bright and long-lasting pulse of high-energy radiation that swept over Earth Sunday, Oct. 9. The emission came from a gamma-ray burst (GRB) – the most powerful class of explosions in the universe – that ranks among the most luminous events known.

On Sunday morning Eastern time, a wave of X-rays and gamma rays passed through the solar system, triggering detectors aboard NASA’s Fermi Gamma-ray Space Telescope, Neil Gehrels Swift Observatory, and Wind spacecraft, as well as others. Telescopes around the world turned to the site to study the aftermath, and new observations continue.

Called GRB 221009A, the explosion provided an unexpectedly exciting start to the 10th Fermi Symposium, a gathering of gamma-ray astronomers now underway in Johannesburg, South Africa. “It’s safe to say this meeting really kicked off with a bang – everyone’s talking about this,” said Judy Racusin, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is attending the conference.


Swift’s X-Ray Telescope captured the afterglow of GRB 221009A about an hour after it was first detected. The bright rings form as a result of X-rays scattered from otherwise unobservable dust layers within our galaxy that lie in the direction of the burst./Credit: NASA/Swift/A. Beardmore (University of Leicester)

The signal, originating from the direction of the constellation Sagitta, had traveled an estimated 1.9 billion years to reach Earth. Astronomers think it represents the birth cry of a new black hole, one that formed in the heart of a massive star collapsing under its own weight. In these circumstances, a nascent black hole drives powerful jets of particles traveling near the speed of light. The jets pierce through the star, emitting X-rays and gamma rays as they stream into space.

The light from this ancient explosion brings with it new insights into stellar collapse, the birth of a black hole, the behavior and interaction of matter near the speed of light, the conditions in a distant galaxy – and much more. Another GRB this bright may not appear for decades.

According to a preliminary analysis, Fermi’s Large Area Telescope (LAT) detected the burst for more than 10 hours. One reason for the burst’s brightness and longevity is that, for a GRB, it lies relatively close to us.

NASA

“This burst is much closer than typical GRBs, which is exciting because it allows us to detect many details that otherwise would be too faint to see,” said Roberta Pillera, a Fermi LAT Collaboration member who led initial communications about the burst and a doctoral student at the Polytechnic University of Bari, Italy. “But it’s also among the most energetic and luminous bursts ever seen regardless of distance, making it doubly exciting.”

The burst also provided a long-awaited inaugural observing opportunity for a link between two experiments on the International Space Station – NASA’s NICER X-ray telescope and a Japanese detector called the Monitor of All-sky X-ray Image (MAXI). Activated in April, the connection is dubbed the Orbiting High-energy Monitor Alert Network (OHMAN). It allows NICER to rapidly turn to outbursts detected by MAXI, actions that previously required intervention by scientists on the ground.

“OHMAN provided an automated alert that enabled NICER to follow up within three hours, as soon as the source became visible to the telescope,” said Zaven Arzoumanian, the NICER science lead at Goddard. “Future opportunities could result in response times of a few minutes.”

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NASA Sets TV Coverage for Crewed Soyuz Mission to Space Station[Live schedule details]

NASA will provide live coverage of key events as a NASA astronaut and two cosmonauts launch and dock to the International Space Station on Wednesday, Sept. 21.

NASA astronaut Frank Rubio and Roscosmos cosmonauts Sergey Prokopyev and Dmitri Petelin will launch aboard the Soyuz MS-22 spacecraft from the Baikonur Cosmodrome in Kazakhstan at 9:54 a.m. EDT Wednesday, Sept. 21 (6:54 p.m. Baikonur time). Coverage will begin at 9 a.m. on NASA Television’s Public Channel, the NASA app, and on the agency’s website.

NASA also will air continuous coverage of an Artemis I tanking test on NASA TV’s Media Channel beginning at 7:15 a.m.

At the Baikonur Cosmodrome in Kazakhstan, NASA astronaut Frank Rubio performs preflight checkouts in the Soyuz MS-22 spacecraft. Rubio is scheduled to launch with crewmates Roscosmos cosmonaut Sergey Prokopyev and Dmitri Petelin Sept. 21 for a six-month mission on the International Space Station.
Credits: NASA/Victor Zelentsov

Soyuz MS-22 launch and key events as well of coverage of the Artemis I tanking test will be available to watch online at:

https://www.nasa.gov/live

After a two-orbit, three-hour journey, the Soyuz will dock to the space station’s Rassvet module at 1:11 p.m. About two hours after docking, hatches between the Soyuz and the station will open and the crew members will greet each other.

Once aboard station, the trio will join Expedition 67 Commander Oleg Artemyev, cosmonauts Denis Matveev and Sergey Korsakov of Roscosmos, as well as NASA astronauts Bob Hines, Kjell Lindgren, and Jessica Watkins, and ESA (European Space Agency) astronaut Samantha Cristoforetti. Rubio, Prokopyev, and Petelin will spend six months aboard the orbital laboratory.

This will be Prokopyev’s second flight into space and the first for Rubio and Petelin.

Mission coverage is as follows (all times Eastern):

Wednesday, Sept. 21

9 a.m. – Coverage begins on NASA TV’s Public Channel for 9:54 a.m. launch.

12:15 p.m. – Coverage begins on NASA TV’s Public Channel for 1:11 p.m. docking.

3:30 p.m. – Coverage begins on NASA TV for hatch opening and welcome remarks.