September 15, 2017, was a bittersweet day for Essam Marouf, Ph.D. After 26 years of analyzing data collected by NASA's Cassini spacecraft, the satellite was sent to its planned, fiery death early that Friday morning.

Dr. Marouf, a professor of electrical engineering at San José State University, was first tapped to work with NASA in 1979 as contributor to the Voyager mission. He was present at NASA's Jet Propulsion Laboratory to witness Cassini's final moments.

"Participating in the Cassini mission from its inception to the very end was a once-in-a-lifetime opportunity," Dr. Marouf says. And while the spacecraft's mission has come to an end, it will give current researchers and many to come a vault of valuable and likely ground-breaking information.

"Much work to complete analysis of the collected data remains, both for us old scientists as well as for future generations of aspiring young explorers eager to learn more about our solar system," he explains.

Marouf's role in the mission specifically centered on one of the spacecraft's 12 instruments, the Radio Science Subsystem (RSS), which used the radio signals transmitted from Cassini to explore Saturn's many properties.

Dubbed as one of the most elaborate space exploration efforts, Cassini gave NASA – by extension the world – its first up-close images of Saturn, its atmosphere, moons and rings.

We spoke with Marouf about his work on Cassini, his reaction to the spacecraft's ending, and what we can take away from the spacecraft's 26-year historic exploration of Saturn.  


Q:  What have we learned from Cassini's mission so far?

Dr. Marouf: Cassini revealed that Saturn's relatively small icy moon, Enceladus, about 500 kilometers across, is one of the few known places in our solar system that could potentially harbor life in a sub-surface ocean of liquid water. Cassini also uncovered the presence of conditions on Saturn's planet-like moon Titan — about 5,000 kilometers across — that resemble what conditions on planet Earth looked like in the early stages of its formation.



Essam Marouf, Ph.D. has worked with NASA since 1979. He was called upon to work on the Cassini mission 26 years ago. Photo courtesy of San José State

Q: What was your role in on Cassini's Radio Science Subsystem (RSS) team?

Dr. Marouf: On the RSS achievements side, one of the major accomplishments has had to wait until almost the last five months of the Cassini mission.

During those months, Cassini executed a daring set of 22 orbits that plunged the spacecraft through a 'free-space' gap between the top of Saturn's atmosphere and the innermost ring region (called Ring D). 

Cassini survived the dives and allowed the collection of fantastic new science due to its unprecedented proximity to Saturn. Its close fly-bys allowed detection of minute disturbances of the frequency of the radio signals transmitted from Cassini to Earth caused by Saturn's gravity. 

A treasure trove of information about the interior structure of Saturn is conveyed by analysis of these disturbances.

Q: You were present at NASA's JPL headquarters during the spacecraft's plunge into Saturn. What were you feeling as you witnessed this?

Dr. Marouf:
 It was hard to watch Cassini disintegrate and burn up in the atmosphere of Saturn the early morning hours of Friday, September 15. Even though such a dramatic end has been planned since 2010, when the mission was extended for the second time, watching the Cassini radio signals go from strong and healthy to dead almost exactly at the predicted time evoked strong emotions and feelings of deep sadness — tears, to be honest.  ​

The sad feelings quickly ceded, however, to overwhelming feelings of pride in what Cassini has accomplished and the science it has returned until that very last moment of its life. Cassini the spacecraft was no more, but Cassini the gold mine of data collected over its 13 years in orbit will live for a long time to come. 


Q: What makes the Cassini mission unlike any other?

Dr. Marouf:  The Cassini mission reflects what's best about us as intelligent beings and our ability to reach out deep in the solar system to explore the backyard of our own home, planet Earth. It was a massive collaborative international effort extending over more than 17 nations, involving close to 300 scientists, and benefiting from contributions of close to 5,000 individuals over its 27 years since the inception of the mission.

Cassini was a 20-year-long symphony played to perfection by teams of imaginative science investigators, competent spacecraft engineers, gifted mission planners, outstanding spacecraft navigators, dedicated science sequencers, and exceptional management teams. Engineers of the NASA and European Space Agency ground receiving stations located on four Earth continents tirelessly listened and recorded the music — rich streams of scientific data — usually lasting a large fraction of a workday.

Cassini simply brought out the best in all of us.

Gallery photos courtesy of NASA