As I was writing this piece during the afternoon of last Friday the15th of September, the “Cassini” space probe of the USA’s National Aeronautics Space Agency (NASA) was reaching the end of a remarkable interplanetary mission which started 20 years ago. Cassini, (named after French astronomer Giovanni Cassini), formed part of the Cassini-Huygens Space-probe-plus-lander which was launched as long ago as October1997, (Christiaan Huygens being another astronomer, a Dutchman this time). The remarkable interplanetary journey to study the giant planet Saturn and its many moons came to a sad but necessary end on Friday when the unmanned probe was deliberately crashed into the ringed planet’s atmosphere so to avoid the risk of an accidental space collision with another heavenly body when Cassini’s batteries ran out. For by then Cassini’s adventure had lasted for almost 20 years.
The Mission was a great piece of international co-operation, a joint effort by the USA’s NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI), the last-named providing the necessary low and high-gain electromagnetic conductors which ensured telecommunications with Earth throughout the mission. With acknowledgements to Wikipedia, NASA and many media sites some interesting information is put before us: Cassini-Huygens’ objectives included determining the structure of the planet, the composition of its surfaces and the dynamic behaviour of Saturn’s rings; and also looking closely at some of Saturn’s more than 60 moons, of which seven new ones were discovered during the course of this mission. These moons vary in dimension from the size of a football field to larger than the planet Mercury. Huygens was landed on Titan, Saturn’s largest moon, and – perhaps this is of even more scientific interest – a close Cassini fly-by of Enceladus revealed huge water-ice geysers erupting from the region of its south pole. Since the presence of water gives the potential for life, this was an intriguing discovery Indeed.
The Journey: Cassini was powered by plutonium-dioxide, whose natural decay can be used to generate DC electricity via thermo-electric generators. Solar arrays were not feasible because of Saturn’s distance from the Sun. Interplanetary speed can be, and was, boosted by “sling-shot navigation”, by which a space probe is thrown further into its desired trajectory by using the gravity of other planets or moons. Cassini made use of this technique several times on its way to Saturn and Titan.
Some facts and figures:
- Start of Mission: 15th October 1997;
- Distance from Earth to Saturn at their closest: 2billion kilometers, which is eight times the distance from Earth to the Sun;
- Cassini’s time taken en route: 6 years and 261days;
- Total Mission Duration; 19 years 335 days
- Fly-by (twice) of Venus: 26th April 1998 and 24thJune 1999;
- Fly-by of Earth+ Moon: 18thAugust 1999;
- Fly-by of Jupiter: 30th December 2000;
- Arrival into Saturn’s orbit: 1st July 2004;
- Huygen’s landing on Titan: 14th January 2005
- End of Mission: 15th September 2017.
At the end of the story we have this quote from Earl Maize, the Cassini Project Manager for Jet Propulsion Laboratory (JPL):
“The Cassini Operations team did an absolutely stellar job guiding the spacecraft to its noble end. From designing this trajectory 7 years ago, to navigating through the 22 nail-biting plunges between Saturn and its rings, this is a crack shot group of scientists and engineers that scripted a fitting end to a great mission”. A comment with which no scientist would disagree.
Conclusion: The cost of such a project is of course enormous, inviting the world to question the appropriateness of spending so many millions/billions of dollars on Space when there are so many alternative uses crying out for funding down here on Earth in the shape of famine, poverty and the consequences of wars and natural disasters. To be human, after all, is to look out for each other, isn’t it? However, the enduring fascination of mankind with the origins, history and characteristics of the universe will no doubt ensure a continuation of research into Astrophysics, Astronautics and these almost-incredible frontier-breaking Odyssies. Hope is only that a better understanding of the whole of Creation will – eventually – lead us to a more intelligent appreciation of our own beautiful planet!
Dick Twomey, in Mauritius’ WEEKLY magazine, 21-27 September 2017