Saturn’s sixth-largest moon, Enceladus, is the brightest world in the solar system, thanks to its shell of brilliant white ice. Beneath that frozen crust is a surprise: a liquid water ocean that could be habitable. If you could zip past Enceladus, you’d see some of that secret ocean yourself in the form of a frigid plume that bursts from the moon like an ice volcano, directing some of its contents to Saturn’s rings and some into space.
For Jason Rabinovitch, assistant professor of mechanical engineering at Stevens Institute of Technology, ice volcanoes in space are all in a day’s work. His research combines computational fluid mechanics and space exploration to cover a wide variety of topics — modeling Enceladus’ plumes, supersonic parachute inflations, plume-surface interactions (i.e. what happens when a spacecraft uses rockets to land) and exploring geophysical phenomena that occur on Earth and other planets, to name a few topics.
Fluid mechanics and space
Scientists use computational fluid mechanics to look at how substances like air and water flow. Their computer simulations model things such as how a parachute will perform in the Martian atmosphere or how the rockets that are used to slow a spacecraft’s descent will churn up the dust on the planet’s surface, potentially throwing up rocks that could damage the lander or dig a crater.
Rabinovitch contributed that expertise to NASA’s Mars 2020 mission when he worked as a mechanical engineer in the Jet Propulsion Laboratory’s Entry, Descent, & Landing (EDL) and Formulation Group. At Mars, it takes about seven minutes for a spacecraft to go from the top of the atmosphere to the surface. This means that a spacecraft only has seven minutes to go from traveling more than 10,000 miles per hour to less than 5 miles per hour at the surface in order to land safely. To help the spacecraft slow down, it uses a large (approximately 20-meter) parachute as part of the descent process, before using rockets to land on the surface. To make sure that there is a high chance of success, many tests and simulations are performed on the Earth before the spacecraft travels to Mars. Validating the computational simulations to ensure that they match what actually happens in reality is an important aspect of all simulations, especially with high-stakes missions where errors are expensive.
“We have to go through what's called a validation process,” Rabinovitch explained. “So, a lot of the time we collaborate with experimentalists, and they will try to run an experiment with a setup that's identical to what we run with a simulation. That way, we can compare the results to see if they're the same.”
In January of 2021, Rabinovitch joined the Stevens faculty. In his lab, students continue to work on those supersonic parachute inflation models and plume-surface interactions, using NASA funding and data from the Mars 2020 mission for the latter.
The lab is also doing simulations for a solid acrylic fuel system that would make it possible to send small satellites on their own long-distance missions. Some smallsats are about the size of a microwave oven and can collect data for a much smaller price tag and on a shorter timeline than sending a big spacecraft — if scientists can propel them to interesting places.
And then there’s those ice volcanoes on Enceladus. “What's been very interesting to scientists is whether or not that ocean actually has the potential to support life,” Rabinovitch mused. “It's very hard to send a spacecraft and even harder to send a probe that could somehow make it through the ice and get into the ocean. So, one of the ideas is to fly in orbit around Enceladus and go through this plume of ice and water and use a scientific instrument to sample that material and figure out what it is.”
For that to work, scientists like Rabinovitch must model how the plumes function to ensure that what gushes out of Enceladus accurately represents the ocean beneath its ice.
The lab also works on yardangs. These natural formations happen in deserts when soft volcanic rock is eroded by wind and dust until they take on aerodynamic, boat-like shapes. Rabinovitch says a desert full of them looks like a boat graveyard. He has been to Argentina twice to collect wind measurements and other data from Earth’s yardangs. Figuring out the conditions that cause them to form on Earth will help unravel how they form on Mars as well.
Rabinovitch’s research combines his lifelong fascination with space exploration with the science that first caught his imagination during his junior year of college—fluid mechanics. Now, he hopes to pass that passion on to his own students at Stevens.
“I teach undergraduate-level and graduate-level fluid mechanics, and, for me, it's fun because I can talk about a lot of the things I like. I make analogies to space exploration or the space program when I can, which I think are some neat examples that people don't necessarily think about,” he explained. “Whenever you teach a course, you continue to learn more about the subject, which I like as well. Hopefully, my enthusiasm for fluid mechanics can come off in some of my lectures.”
Here, from out there
That enthusiasm has recently taken on a new life as Rabinovitch contemplates another stream of research focused on addressing the challenges of climate change.
“The more we learn about our solar system and space, the more we can understand things on the Earth,” he said. “And I think space missions are great for international collaboration and inspiring the next generation of scientists.”
Rabinovitch says studying Venus is a good example since some scientists think the hottest planet in the solar system was once like Earth before an extreme greenhouse effect changed it. He also points to the value of Earth-observing missions, which can generate tons of data for climate scientists and even play a role in policy by helping monitor how well individual nations hold up their ends of climate change agreements.
“I'm a huge Star Trek and Star Wars fan,” he noted. “And I think it would be great in the future if we could be a multi-world species, but in the short term, and with all the exponentially increasing effects of climate change, I think we really need to focus on what we have here and use everything we understand about the solar system to improve life on Earth.”