Space Matter: A Brief History of Cassini

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Space Matter is a weekly column that delves into space science and the mechanics of spaceflight. From the latest discoveries in the universe around us to the fits and starts of rocket test flights, you’ll find analysis, discussion and an eternal optimism about space and launching ourselves into the cosmos.

If you follow space news, you may have been hearing about the end of the Cassini mission for a while now. What is this spacecraft, and why does it matter?

Cassini-Huygens is a orbiter-lander pair that launched in 1997 to Saturn. Cassini was to orbit Saturn in a long, elliptical orbit, which would both protect the spacecraft from radiation and also allow for multiple flybys of Saturn’s moons, while the Huygens lander would detach and land on Titan’s rocky surface. The little lander was only constructed to send signals for a few hours, while Cassini was in orbit, but radio telescopes have told us that it continued to transmit long after its primary mission concluded.

Why Titan for a lander? Well, we have many moons in our solar system, but Titan has a thick, dense atmosphere, composed primarily of methane. It may even be capable of supporting life.

We’re approaching the end of Cassini’s final mission, so let’s take this opportunity to review a timeline of the spacecraft’s mission and bid a fond farewell to this hard-working spacecraft.

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1982: A Saturn Orbiter and Titan Probe dual mission is proposed for the first time by European scientists. Over the next few years, it develops into a joint NASA-ESA (European Space Agency) mission.

1994: Cassini-Huygens overcomes political hurdles in the U.S. Congress; it was in danger of cancellation due to budget cuts, but NASA is able to convince Congress that stopping the project after the ESA had already funded their side would be a bad idea.

1997: Liftoff! Cassini-Huygens launched from Cape Canaveral Air Force Station in Florida at 4:43 AM on October 15, 1997.

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Cassini-Huygens launch. Photo: NASA/JPL/KSC

1998: Cassini-Huygens used Venus for a gravity assist to adjust its course and increase its speed. Gravity assists (or a slingshot) occur when a spacecraft uses the gravity of a planet (or other celestial body that has a certain amount of gravity) to change its speed and path without having to utilize engines or consume fuel. As Venus pulled on Cassini-Huygens, it was able to increase the spacecraft’s speed by about 7 km/s. The spacecraft would go onto a second Venus flyby in June 1999 and an Earth flyby in August 1999.

2000: The spacecraft grabbed a gravity assist from Jupiter, snapping some pretty great pictures in the process. The entire flyby took about 6 months.

Cassini snapped this amazing picture of Jupiter on its way to Saturn. Photo: NASA/JPL/Space Science Institute

2004: The gravity of Saturn overtakes the gravity of the Sun as the dominant influence on Cassini-Huygens. Cassini makes its way closer to the ringed planet and eventually arrives on June 30, taking pictures of and flying by its moons in the process. On December 24, the Huygens landing probe separates from the orbiter.

2005: Huygens arrives at Titan on January 14 and begins landing procedures. Two hours later, it lands on the surface of the moon. Scientists are still in the process of analyzing its data, over a decade later. Cassini continues with its moon flybys, experiencing close encounters with Titan, Enceladus, Hyperion, Dione, and Rhea. The spacecraft also discovers a new moon within Saturn’s rings, called Daphnis, and sees plumes of water ice and organic particles ejected from the surface of Enceladus.

Daphnis is visible in the top left of this image, within Saturn’s rings. Photo: NASA/JPL/Space Science Institute

2006: Cassini continues with multiple flybys of Titan, discovering lakes on the moon in July.

2008: Cassini ends its primary mission with a final flyby of Titan. Its mission is extended to observe the Equinox of Saturn, or Saturn’s summer, when the Sun is directly above its equator. Meanwhile, scientists confirm that Huygens discovered liquid hydrocarbons in Titan’s polar regions to the north. Hydrocarbons are organic compounds, and while this could mean the moon is able to support life, it also means the potential for a much richer source of fossil fuels than Earth has been able to provide.

Titan, with Saturn in the background. Photo: NASA/JPL-Caltech/Space Science Institute

2010: In February, NASA announces a second mission extension of Cassini, from September 2010 through May 2017. The mission includes 155 orbits of Saturn, with 54 flybys of Titan, 11 flybys of Enceladus, three of Dione, and two of Rhea. In December of 2010, Cassini discovers a giant storm in the northern regions of Saturn.

2011-2016: Cassini continues with its mission and flybys, making important discoveries. In 2015, it finds that Enceladus’ liquid water plumes are fueled by a global liquid ocean underneath an icy crust.

Water ice particles flying into space from Enceladus. Photo: NASA/JPL/Space Science Institute

2017: And here we are to bid Cassini a fond farewell. This week, Cassini is scheduled to begin its first Grand Finale dive, which is a daring series of orbits that will take the spacecraft between the planet and its rings. For 22 orbits, Cassini will analyze its the planet’s atmosphere, the composition of its rings, and hopefully send us the closest pictures we’ve ever gotten of both Saturn and its rings.

All of this comes to a grand end on September 15, 2017, when Cassini will make its final dive into Saturn’s atmosphere, with a controlled impact into the gas giant. This choice was deliberate, as scientists want to prevent Cassini from possibly contaminating one of Saturn’s moons that are capable of supporting life.

Venus as seen through the rings of Saturn. Photo: NASA/JPL-Caltech/Space Science Institute

The next few months should bring some grand images from Cassini, but take some time to admire this little spacecraft that could; almost a decade after its primary mission, it’s still sending us valuable information that will help scientists understand our place in the universe.

Top photo courtesy of NASA/JPL-Caltech/Space Science Institute

Swapna Krishna is a freelance writer, editor and giant space/sci-fi geek.