Cassini - A Lone Explorer

Cassini - A Lone Explorer

Launched in on Oct. 15, 1997, Cassini's mission to explore Saturn ended on Sept. 15, 2017 with a deliberate plunge into Saturn's atmosphere. The spacecraft collected and transmitted data until the very last seconds of the mission.

Cassini was a half part of this mission and another half part was Huygens lander which would be landed on Saturn's largest moon, Titan.

The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.

The Huygens module traveled with Cassini until its separation from the probe on December 25, 2004; it was landed by parachute on Titan on January 14, 2005. It returned data to Earth for around 90 minutes, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than our own.

This unprocessed image of the Saturn system was taken by NASA's Cassini spacecraft on Sept. 13, 2017. It is among the last images Cassini will send back. Credit: NASA/JPL-Caltech/Space Science Institute.

Huygens view of Titan's surface

Cassini's Plutonium power source

Because of Saturn's distance from the Sun, solar arrays were not feasible as power sources for this space probe.To generate enough power, such arrays would have been too large and too heavy.Instead, the Cassini orbiter was powered by three radioisotope thermoelectric generators (RTGs), which use heat from the natural decay of about 33 kg (73 lb) of plutonium-238 (in the form of plutonium dioxide) to generate direct current electricity via thermoelectrics. The RTGs on the Cassini mission have the same design as those used on the New Horizons, Galileo, and Ulysses space probes, and they were designed to have very long operational lifetimes.At the end of the nominal 11-year Cassini mission, they were still able to produce 600 to 700 watts of electrical power.(One of the spare RTGs for the Cassini mission was used to power the New Horizons mission to Pluto and the Kuiper belt, which was designed and launched later.

To gain momentum while already in flight, the trajectory of the Cassini mission included several gravitational slingshot maneuvers: two fly-by passes of Venus, one more of the Earth, and then one of the planet Jupiter. The terrestrial flyby was the final instance when the probe posed any conceivable danger to human beings. The maneuver was successful, with Cassini passing by 1,171 km (728 mi) above the Earth on August 18, 1999.Had there been any malfunction causing the probe to collide with the Earth, NASA's complete environmental impact study estimated that, in the worst case (with an acute angle of entry in which Cassini would gradually burn up), a significant fraction of the 33 kg of plutonium-238 inside the RTGs would have been dispersed into the Earth's atmosphere so that up to five billion people (i.e. almost the entire terrestrial population) could have been exposed, causing up to an estimated 5,000 additional cancer deaths over the subsequent decades (0.0005 per cent, i.e. a fraction 0.000005, of a billion cancer deaths expected anyway from other causes; the product is incorrectly calculated elsewhere as 500,000 deaths). However, the chance of this happening were estimated to be less than one in one million.

Unique Science

As Cassini plunged past Saturn, the spacecraft collected some incredibly rich and valuable information that was too risky to obtain earlier in the mission:

• The spacecraft made detailed maps of Saturn's gravity and magnetic fields, revealing how the planet is arranged internally, and possibly helping to solve the irksome mystery of just how fast Saturn is rotating.
• Cassini's particle detectors sampled icy ring particles being funneled into the atmosphere by Saturn's magnetic field.
• Its cameras took amazing, ultra-close images of Saturn's rings and clouds.
• The final dives vastly improved our knowledge of how much material is in the rings, bringing us closer to understanding their origins.

Saturn reached equinox in 2008, shortly after the end of the prime mission.

Why End the Mission?

By 2017, Cassini had spent 13 years in orbit around Saturn, following a seven-year journey from Earth. The spacecraft was low on the rocket fuel used for adjusting its course. If left unchecked, this situation would have eventually prevent mission operators from controlling the course of the spacecraft.

Two moons of Saturn, Enceladus and Titan, have captured news headlines over the past decade as Cassini data revealed their potential to contain habitable – or at least "prebiotic” – environments.

In order to avoid the unlikely possibility of Cassini someday colliding with one of these moons, NASA chose to safely dispose of the spacecraft in the atmosphere of Saturn. This ensured that Cassini could not contaminate any future studies of habitability and potential life on those moons.

Titan's surface was imaged by looking through the atmosphere in 2004, but some clouds remain visible.