Cassini: Doom Without Gloom
An engineer’s firsthand account of space history in the making.
By Deborah Jackson
There are times of discovery when the world’s before and after views represent a sudden paradigm shift. For example, when the single surviving ship from Ferdinand Magellan’s original five limped back to Spain after three years circumnavigating the globe, the geopolitical conception of the world changed forever. In the before view, no proof existed that the Earth was round; in the after view, decision-makers could chart a route around the world by sea.
Another example is how our perception of the solar system has changed over a 20-year span. In the before view, we had nine planets—named for Greek and Roman gods—in our solar system and inferred what we could about them based on telescope observations: Venus was covered in clouds, Mars had red canals, Saturn had rings and four moons, Jupiter was the largest, and Pluto, the smallest, was nonetheless an undisputed planet. Then in 1977, NASA launched two Voyager spacecraft on a grand tour of the mysterious outer planets. As data flowed back to the space agency, filling in knowledge gaps on the solar system’s makeup, the after view came into focus. We learned that Venus is uninhabitable at 864 degrees Fahrenheit, Jupiter and Saturn had a whopping 63 and 62 moons, respectively, and all of the outer planets have ring systems, although none as spectacular as Saturn’s. The Grand Tour also revealed that one planet, Uranus, actually rotates on an axis that lies in the Plane of the Ecliptic instead of perpendicular to it. These facts are known only because of the collective efforts of the huge team of engineers and scientists supporting the Voyager mission. Although the project manager and the chief scientist represent the face of a mission, one should not forget that the magnitude of the effort requires a massively large but well-functioning team.
Twenty years after Voyager, NASA initiated a follow-on mission motivated by these discoveries. Launched in October 1997, the Cassini mission was a collaboration between NASA, the European Space Agency, and the Italian Space Agency. Its purpose was to further explore the rings and moons of Saturn. As the cognizant engineer for the Cassini Radio Science Subsystem (RSS), I delivered the RSS instrument to the Jet Propulsion Lab for assembly, test, and launch operations (ATLO). Although I was excited to be part of the endeavor, the reality was more complex than I initially expected. My concerns about our ability to complete the assembly and testing and put the spacecraft through its paces in time for an October launch were quickly put to rest by Julie Webster, the Cassini ATLO test conductor, who confidently assured me that we had plenty of time.
The first time we stacked the spacecraft to begin electronic integration and system validation, hundreds of scientists and engineers from 28 countries (anyone who built and delivered a subsystem for integration) participated. There we were, tuned into the radio net, working around the clock to validate the probe’s subsystems as they were powered on, one by one. For me, this was when it hit home that the Cassini endeavor would forever imprint history with discoveries. My imagination soared even higher when a memo went around asking Cassini team members—more than 1,000 people—if we wanted our names etched onto a plaque that would be mounted and flown on a spacecraft panel as a permanent record of our participation. Adding my name to the list, I imagined future space adventurers stumbling across a defunct Cassini probe to find my name among the many hundreds of others on the plaque. But alas, in the interest of science, an enduring legacy was not to be.
Fast forward 20 years: The Cassini mission, initially designed for an 11-year stint, was so successful that it was extended another nine years. By this time, the data collected by the probe had revealed a new after view, including the potential for two of Saturn’s moons, Enceladus and Titan, to contain habitable—or at least “prebiotic”—environments. The desire to keep the moons pristine for future studies of habitability and potential life meant that the Cassini probe could not be left to drift in a random orbit. Instead, Chief Engineer Julie Webster, who had guided us through the spacecraft assembly and later nursed the probe through its 20-year mission, sent the final command to plunge Cassini into Saturn so it could burn up safely.
Deborah Jackson is a program manager in the National Science Foundation’s Engineering Directorate. The views expressed in the article do not necessarily represent those of NSF or of the U.S. government.