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Cassini–Huygens: the story on HearLore | HearLore
— Ch. 1 · Origins of a Global Endeavor —
Cassini–Huygens.
~8 min read · Ch. 1 of 7
The Cassini, Huygens mission began its life in 1982 when the European Science Foundation and the American National Academy of Sciences formed a working group. Two European scientists suggested a paired Saturn Orbiter and Titan Probe as a possible joint mission. NASA's Solar System Exploration Committee recommended the same Orbiter and Probe pair as a core NASA project in 1983. A joint study between NASA and the European Space Agency ran from 1984 to 1985. ESA continued with its own study in 1986 while American astronaut Sally Ride examined the mission in her influential 1987 report. The report described the Saturn orbiter and probe as a NASA solo mission initially.
In 1988, Len Fisk returned to the idea of a joint NASA and ESA mission. He wrote to his counterpart at ESA, Roger Bonnet, strongly suggesting that ESA choose the Cassini mission from three candidates. Fisk promised that NASA would commit to the mission as soon as ESA did. Late in 1988, ESA chose Cassini, Huygens as its next major mission. The following year the program received major funding in the US. The collaboration improved relations between the two space programs but also helped Cassini, Huygens survive congressional budget cuts in the United States.
The project came under fire politically in both 1992 and 1994. NASA successfully persuaded the United States Congress that it would be unwise to halt the project after ESA had already poured funds into development. Citizens' groups concerned about the potential environmental impact attempted to derail it through protests and lawsuits until and past its 1997 launch. The project proceeded politically smoothly after 1994 despite these challenges.
Engineering a Nuclear Powerhouse
NASA's Jet Propulsion Laboratory managed the mission where the orbiter was assembled. The European Space Research and Technology Centre developed Huygens with Aérospatiale of France assembling the probe. The Italian Space Agency provided the Cassini orbiter's high-gain radio antenna along with other equipment. The spacecraft was planned to be the second three-axis stabilized, RTG-powered Mariner Mark II. Budget cuts forced NASA to terminate CRAF development to save Cassini so the Mariner Mark II series was cancelled.
The combined orbiter and probe was at the time the third-largest uncrewed interplanetary spacecraft ever successfully launched. The orbiter had a mass of 5,712 kilograms while the probe weighed 350 kilograms including support equipment left on the orbiter. With the launch vehicle adapter and propellants at launch, the spacecraft had a total mass of 5,680 kilograms. Cassini was 6.9 meters high and 4 meters wide. Its bus was a dodecagonal prism atop a conical frustum connecting it to a cylinder containing the propellant tanks.
Cassini had 1,630 interconnected electronic components and 22,000 wire connections. The core control computer CPU used a redundant system with the MIL-STD-1750A instruction set architecture. The main propulsion system consisted of one prime and one backup R-4D bipropellant rocket engine. Cassini was powered by 720 kilograms of nuclear fuel mainly plutonium dioxide. The heat from the material's radioactive decay turned into electricity via three GPHS-RTG radioisotope thermoelectric generators.
When did the Cassini Huygens mission begin and end?
The Cassini Huygens mission began its life in 1982 when a working group formed between the European Science Foundation and the American National Academy of Sciences. The mission ended with a dive into Saturn's atmosphere on the 15th of September 2017.
Who managed the Cassini orbiter and who built the Huygens probe?
NASA's Jet Propulsion Laboratory managed the mission where the orbiter was assembled. The European Space Research and Technology Centre developed Huygens with Aérospatiale of France assembling the probe.
What major discovery did Cassini make about Titan in July 2006?
Radar images obtained on the 21st of July 2006 appeared to show lakes of liquid hydrocarbon such as methane and ethane in Titan's northern latitudes. This is the first discovery of currently existing lakes anywhere besides on Earth.
How much did the Grand Finale phase of the Cassini mission cost?
The U.S. government approved the Grand Finale at the cost of $200 million in late 2014. This amount was far cheaper than building two new probes in separate Discovery-class missions.
When did Cassini enter orbit around Saturn after its seven-year voyage?
Cassini achieved orbit after a seven-year voyage on the 1st of July 2004. It was the first spacecraft to orbit Saturn.
Launched aboard a Titan IVB/Centaur on the 15th of October 1997, Cassini spent almost seven years in transit before entering orbit around Saturn. The voyage included flybys of Venus on the 26th of April 1998, and the 24th of June 1999. These flybys provided the space probe with enough momentum to travel all the way out to the asteroid belt. On the 18th of August 1999, at 03:28 UTC, the craft made a gravitational-assist flyby of Earth. One hour and 20 minutes before closest approach, Cassini made its closest approach to the Earth's Moon at 377,000 kilometers.
On the 23rd of January 2000, Cassini performed a flyby of the asteroid 2685 Masursky at around 10:00 UTC. It took photos in the period five to seven hours before the flyby at a distance of 500 kilometers. Cassini made its closest approach to Jupiter on the 30th of December 2000, at 9.7 million kilometers. About 26,000 images of Jupiter, its faint rings, and its moons were taken during the six-month flyby.
The spacecraft flew through the gap between the F and G rings and achieved orbit after a seven-year voyage on the 1st of July 2004. It was the first spacecraft to orbit Saturn. The Saturn Orbital Insertion maneuver required the craft to orient its High-Gain Antenna away from Earth and along its flight path. Once the craft crossed the ring plane, it had to rotate again to point its engine along its flight path. Then the engine fired to decelerate the craft by 622 meters per second to allow Saturn to capture it.
Descent Into Titan's Haze
Cassini released the Huygens probe on the 25th of December 2004, by means of a spring and spiral rails intended to rotate the probe for greater stability. It entered the atmosphere of Titan on the 14th of January 2005, and after a two-and-a-half-hour descent landed on solid ground. Although Cassini successfully relayed 350 of the pictures that it received from Huygens of its descent and landing site, a malfunction in one of the communications channels resulted in the loss of a further 350 pictures.
The data were transmitted by a radio link between Huygens and Cassini provided by Probe Data Relay Subsystem. As the probe's mission could not be telecommanded from Earth because of the great distance, it was automatically managed by the Command Data Management Subsystem. The PDRS and CDMS were provided by the Italian Space Agency. A work-around was found to recover the mission when data sent from the Huygens probe to Cassini orbiter would be largely unreadable due to narrow bandwidth signal processing electronics.
Radar images obtained on the 21st of July 2006, appeared to show lakes of liquid hydrocarbon such as methane and ethane in Titan's northern latitudes. This is the first discovery of currently existing lakes anywhere besides on Earth. The lakes range in size from one to one-hundred kilometers across. On the 13th of March 2007, the Jet Propulsion Laboratory announced that it had found strong evidence of seas of methane and ethane in the northern hemisphere of Titan.
Enceladus Geysers and Hidden Oceans
During the first two close flybys of the moon Enceladus in 2005, Cassini discovered a deflection in the local magnetic field that is characteristic for the existence of a thin but significant atmosphere. Other measurements obtained at that time point to ionized water vapor as its main constituent. Cassini also observed water ice geysers erupting from the south pole of Enceladus which gives more credibility to the idea that Enceladus is supplying the particles of Saturn's E ring.
On the 12th of March 2008, Cassini made a close fly-by of Enceladus passing within 50 kilometers of the moon's surface. The spacecraft passed through the plumes extending from its southern geysers detecting water carbon dioxide and various hydrocarbons with its mass spectrometer. On the 21st of November 2009, Cassini made its eighth flyby of Enceladus approaching within 49 kilometers of the surface.
On the 3rd of April 2014, nearly ten years after Cassini entered Saturn's orbit, NASA reported evidence of a large salty internal ocean of liquid water in Enceladus. The presence of an internal salty ocean in contact with the moon's rocky core places Enceladus among the most likely places in the Solar System to host alien microbial life. In September 2015, NASA announced that gravitational and imaging data from Cassini were used to analyze the librations of Enceladus's orbit.
Rings Hexagons and Seasonal Shifts
In May 2005, Cassini began a series of radio occultation experiments to measure the size-distribution of particles in Saturn's rings. For over four months, the craft completed orbits designed for this purpose. During these experiments, it flew behind the ring plane of Saturn as seen from Earth and transmitted radio waves through the particles. The radio signals received on Earth were analyzed for frequency phase and power shift of the signal to determine the structure of the rings.
Between 2012 and 2016, the persistent hexagonal cloud pattern at Saturn's north pole changed from a mostly blue color to more of a golden color. One theory for this is a seasonal change: extended exposure to sunlight may be creating haze as the pole swivels toward the Sun. It was previously noted that there was less blue color overall on Saturn between 2004 and 2008.
On the 25th of October 2012, Cassini witnessed the aftermath of the massive Great White Spot storm that recurs roughly every 30 years on Saturn. Data from the composite infrared spectrometer indicated a powerful discharge from the storm that caused a temperature spike in the stratosphere of Saturn 1,000 degrees above normal. Simultaneously, a huge increase in ethylene gas was detected by NASA researchers at Goddard Research Center in Greenbelt Maryland.
The Final Dive Into Saturn
Cassini end, named the Grand Finale, involved a series of close Saturn passes approaching within the rings then an entry into Saturn's atmosphere on the 15th of September 2017, to destroy the spacecraft. This method was chosen to ensure protection and prevent biological contamination to any of the moons of Saturn thought to offer potential habitability. In 2008, a number of options were evaluated to achieve this goal each with varying funding scientific and technical challenges.
There were problems in 2013, 14 about NASA receiving U.S. government funding for the Grand Finale. The two phases of the Grand Finale ended up being the equivalent of having two separate Discovery-class missions in that the Grand Finale was completely different from the main Cassini regular mission. The U.S. government in late 2014 approved the Grand Finale at the cost of $200 million. This was far cheaper than building two new probes in separate Discovery-class missions.
A final Titan flyby on the 22nd of April 2017, changed the orbit again to fly through the gap between Saturn and its inner ring days later on April 26. Cassini passed about 180 kilometers above Saturn's cloud layer and 4,800 kilometers from the visible edge of the inner ring. After a further 22 orbits through the gap, the mission was ended with a dive into Saturn's atmosphere on September 15. Signal was lost at 11:55:46 UTC on the 15th of September 2017, 30 seconds later than predicted.