Thursday, November 17, 2016

Cassini



Recently I wrote a sad lament for the Schiaparelli Lander, even as I praised those who had successfully inserted the Trace Gas Orbiter (TGO) into a near-perfect orbit around Mars. This orbiting communications relay and atmospheric laboratory will serve NASA scientists for the next several years and will eventually support a European Space Agency (ESA) rover on the planetary surface. TGO and the Schiaparelli lander had traveled to the Red Planet together but the lander’s fate was sealed when its landing rockets fired improperly.

On the other hand, NASA’s Cassini–Huygens spacecraft was launched in 1997 and arrived in orbit around Saturn in 2004 where both portions of the craft performed flawlessy. As planned, the Huygens lander made a successful touchdown on one of Saturn’s moons (Titan) and transmitted data throughout the landing and approximately 90 minutes of its initial time on the surface. This made Huygens the first Earth vehicle to land on the surface of any planet or moon beyond the asteroid belt of our solar system. Cassini went on to explore Titan and other moons before settling into an orbit around Saturn.

Since leaving Earth in 1997, Cassini has been an amazing spacecraft. Launched in a time when 1-mega-pixel cameras were state-of-the-art, that was the best high-resolution camera with which it could be equipped. Now, most cell-phones carry an 8 to 12 mega-pixel camera. Such are the changes that come with a 20-year mission. Cassini was the first spacecraft to orbit Saturn, and it has been able to map Saturn’s magnetosphere, has found new Saturnine moons, and studied Saturn’s atmosphere and rings with greater precision than ever before. But, the space-vehicle is getting old. In terms of how much space debris, radiation, and other hazards it has seen, relatively speaking, it is older than the last incarnation of Spock. Automobiles that are 20 years old and older are often considered antique and show up in enthusiast’s collections; this 20-year-old vehicle is still out there serving well.

Numerous remote repairs, software updates, and “farmer-fixes” have had to be performed on this machine to keep it on track; and, by the marvels of contemporary engineering, the technicians at NASA have indeed kept it on its mission. Cassini has two main engines and is still using its primary engine, but those who work on this machine had to switch it over to the back-up attitude-control-thrusters when the first set began to fail several months ago.

There is still an end of the road for even a highly successful mission like Cassini-Huygens. At the end of this month, Cassini’s thrusters will maneuver it into a position that will allow for 22 orbits close to the rings, through gaps between rings, and finally between the Saturnine atmosphere and the inner-most ring. As a Grand Finale (a term actually being used for the final days of this spacecraft), Cassini will plunge into the atmosphere in September of 2017 where it will be vaporized by the heat of friction and crushed by the pressure of the atmosphere. It will indeed be a magnificent curtain-call for one of the most successful space missions of all time.

Links used in researching this article:
https://saturn.jpl.nasa.gov/news/2947/care-and-feeding-of-an-aging-spacecraft/

An interesting hexagonal polar vortex at the north pole of Saturn:




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