Cassini Probe: The Final Signal

by Donovan Makus

 

September 15th marked the second Friday since school began and the end of the Cassini probe, a joint project between NASA and the European and Italian space agencies. Predeceased by its partnered lander, the Huygens probe, Cassini continued to make discoveries well after its original mission had ended. Exhibiting the devotion to duty that is expected from any well-engineered spacecraft, Cassini provided valuable data until its end when it crashed through Saturn’s atmosphere at speeds of over 100,000 km/h. It had previously transmitted data for longer than expected, concluded the primary objective of its almost 20-year mission, and became the first atmospheric probe of Saturn.

Originally dreamed up in the 1980s, the 2,500 kg, 6.7 by 4-meter joint American-European Cassini-Huygens probe was launched on a Titan IVB/Centaur on October 15th, 1997. Named after two pioneering scientists, Cassini-Huygens spent most of its early life commuting, completing an almost seven-year journey before reaching Saturn in July of 2004. This is a commute that not even an international student can match. This time wasn’t wasted, however, as it completed flybys of Venus, Earth, Jupiter, and the “2685-Masursky” asteroid, while using the gravitational pull of the planets to execute slingshot acceleration maneuvers. Cassini’s original mission was slated to last almost four years (June 2004 to May 2008) but was extended three times, culminating with the “Grand Finale” mission, which ended the spacecraft’s service.

Both the Cassini probe and its paired Huygens lander supplied enlightening scientific advances during their long service. On Saturn, Cassini observed a large stationary hurricane on Saturn’s north pole with a 2,000 km wide eye and 530 km/h winds despite the low amount of water vapour found on the planet. Researchers hope to use data from that hurricane to better understand hurricanes on Earth. Cassini was also able to detect a storm that typically occurs once every 30 years, the “Great Storm of 2010,” observing an 83 Celsius temperature spike. The probe was also able to study Saturn’s signature rings from unprecedented detail within its orbit, supplying new information on their composition and distribution and detecting particles in the rings ranging in size from a grain of sand to as large as mountains. Cassini also discovered plumes of water on Enceladus, one of Saturn’s moons, as well as the internal reservoirs of water that supply these plumes; this is obviously an exciting discovery as water is critical to much of the life we see on Earth. This discovery has broad implications in the search for life outside of Earth. On Titan, Saturn’s largest moon, Cassini was able to observe methane rain, rivers, and seas. Cassini also discovered seven new moons orbiting Saturn. The Huygens lander also collected data on the composition of Titan, relaying it to Earth through Cassini, while being party to many firsts: the first spacecraft to land on Titan, another of Jupiter’s moons, and being the first spacecraft to successfully land in the outer solar system.

None of these discoveries would have been possible without the spacecraft’s sophisticated sensors and design. Cassini boasted 12 scientific instruments which can conduct 27 different scientific tests, ranging from optical sensors operating in the ultraviolet, infrared, and visible bands, to magnetometers and instruments used to analyze plasma. On any spacecraft, space is at a premium, and Cassini boosts multi-purpose technologies, such as its radar using the high-gain antenna that is also used to communicate with Earth. Unlike other spacecraft, Cassini operated too far away from our Sun to use solar energy as its power source. Instead, it required the use of 33 kg of Plutonium-238 in three generators, harnessing the power of nuclear energy. Plutonium dioxide was also used in 117 small heaters, 82 on Cassini, and 35 on Huygens, each generating one watt of power to keep the spacecraft from being damaged by the cold. All of these sensors would have been for naught if it were not for Cassini’s communications sensor suite, which boasted one primary high-gain antenna with backup low-gain antennas. But even with the advanced technology, Cassini could not overcome distance; transmissions from Cassini to Earth took over an hour to arrive.

As Chaucer once said, all good things must come to an end, and the same goes for Cassini. Despite exceeding the original mission timetable, physics dictated that Cassini’s three plutonium-238 generators lost power over time, leading to concern that Cassini would lose all power and be left adrift. This could have lead to Cassini crashing into one of Saturn’s moons, allowing microbes from Earth (unwanted interplanetary hitchhikers) to infect these moons. This would have disrupted their existing environment and harmed future attempts to search for and understand life on surrounding planets. To prevent this, Cassini’s last mission was a series of close passes through Saturn’s rings before it burned up in Saturn’s atmosphere. It sent data until the stress of reentry was too great, which resulted in its disintegration after consuming its rocket propellant.

Almost 20 years after being launched, Cassini-Huygens has collected 635 GB of data, traveled 4.9 billion miles, taken 453,048 images, and been part of 3,948 scientific papers. The total cost of the Cassini-Huygens for the entire life of the program came to 3.9 billion dollars, and the program employed more than 5,000 people. Lessons learned from the program will be applied to future projects, such as the planned Europa Clipper, which will perform a similar mission orbiting Jupiter. Technology from the project has been used on other projects, such as a spare plutonium generator being used to power the New Horizons spacecraft. As the quest to deepen our knowledge of our planetary neighbours continues, Cassini-Huygens will be remembered for its contribution to our never-ending quest for cosmic knowledge.


Almost 20 years after being launched, Cassini-Huygens has collected 635 GB of data, travelled 4.9 billion miles, taken 453,048 images, and been part of 3,948 scientific papers. The total cost of the Cassini-Huygens for the entire life of the program came to $3.9 billion USD, and the program employed more than 5,000 people. Lessons learned from the program will be applied to future projects, such as the planned Europa Clipper, which will perform a similar mission orbiting Jupiter. Technology from the project has been used on other projects, such as a spare plutonium generator being used to power the New Horizons spacecraft. As the quest to deepen our knowledge of our planetary neighbours continues, Cassini-Huygens will be remembered for its contribution in our never-ending quest for cosmic knowledge.

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