Cassini–Huygens is an unmanned spacecraft sent to the planet Saturn. It is a flagship-class NASA-ESA-ASI robotic spacecraft sent to the Saturn system. It has studied the planet and its many natural satellitessince arriving there in 2004, also observing Jupiter, the heliosphere, and testing the theory of relativity. Launched in 1997 after nearly two decades of development, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan called Huygens, which entered and landed on Titan in 2005. Cassini is the fourth space probe to visit Saturn and the first to enter orbit, and its mission is ongoing as of 2014. The two-part spacecraft is named after astronomers Giovanni Cassini and Christiaan Huygens.
The spacecraft launched on October 15, 1997 aboard a Titan IVB/Centaur and entered orbit around Saturn on July 1, 2004, after an interplanetary voyage which included flybys of Earth, Venus, and Jupiter. On December 25, 2004, Huygens separated from the orbiter at approximately 02:00 UTC. It reached Saturn's moon Titan on January 14, 2005, when it entered Titan's atmosphere and descended to the surface. It successfully returned data to Earth, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System.
Nearly a decade after entering orbit, on April 3, 2014, NASA reported that evidence for a large underground ocean of liquid water on Enceladus, a moon of Saturn, had been found by Cassini. According to scientists, evidence of an underground ocean suggests that Enceladus is one of the most likely places in the solar system to "host microbial life". On June 30, 2014, NASA celebrated ten years of Cassini exploring Saturn and its moons, highlighting the discovery of water activity on Enceladus among other findings.
OVERVIEW:
Sixteen European countries and the United States make up the team responsible for designing, building, flying and collecting data from the Cassini orbiter and Huygens probe. The mission is managed by NASA’s Jet Propulsion Laboratory in the United States, where the orbiter was assembled. Huygens was developed by the European Space Research and Technology Centre. The Centre's prime contractor, Aérospatiale of France (now Thales Alenia Space), assembled the probe with equipment and instruments supplied by many European countries (Huygens' batteries and two scientific instruments by the United States). The Italian Space Agency (ASI) provided the Cassini orbiter's high-gain radio antenna, with the incorporation of a low-gain antenna (that ensure telecommunications with the Earth for the entire duration of the mission), a compact and lightweight radar, which also uses the high-gain antenna and serves as a synthetic aperture radar, a radar altimeter, a radiometer, the radio science subsystem (RSS), the visible channel portion VIMS-V of VIMS spectrometer (the VIMS-IR counterpart was provided by NASA, as well as Main Electronic Assembly, which includes electronic subassemblies provided by CNES of France).
On April 16, 2008, NASA announced a two-year extension of the funding for ground operations of this mission, at which point it was renamed to the Cassini Equinox Mission. This was again extended in February 2010 with the Cassini Solstice Mission.
OBJECTIVES:
Cassini has seven primary objectives:
Cassini–Huygens was launched on October 15, 1997, from Cape Canaveral Air Force Station's Space Launch Complex 40 using a U.S. Air Force Titan IVB/Centaur rocket. The complete launcher was made up of a two-stage Titan IV booster rocket, two strap-on solid rocket motors, the Centaur upper stage, and a payload enclosure, or fairing.
The total cost of this scientific exploration mission is about US$3.26 billion, including $1.4 billion for pre-launch development, $704 million for mission operations, $54 million for tracking and $422 million for the launch vehicle. The United States contributed $2.6 billion (80%), the ESA $500 million (15%), and the ASI $160 million (5%).
The primary mission for Cassini was completed on July 30, 2008. The mission was extended to June 2010 (Cassini Equinox Mission). This studied the Saturn system in detail during the planet's equinox, which happened in August 2009. On February 3, 2010, NASA announced another extension for Cassini, lasting 6½ years until 2017, ending at the time of summer solstice in Saturn's northern hemisphere (Cassini Solstice Mission). The extension enables another 155 revolutions around the planet, 54 flybys of Titan and 11 flybys of Enceladus. In 2017, an encounter with Titan will change its orbit in such a way that, at closest approach to Saturn, it will be only 3,000 km above the planet's cloudtops, below the inner edge of the D ring. This sequence of "proximal orbits" will end when another encounter with Titan sends the probe into Saturn's atmosphere.
SPACE CRAFT DESIGN:
The spacecraft was originally planned to be the second three-axis stabilized, RTG-powered Mariner Mark II, a class of spacecraft developed for missions beyond the orbit of Mars.
Cassini was developed simultaneously with the Comet Rendezvous Asteroid Flyby (CRAF) spacecraft, but various budget cuts and rescopings of the project forced NASA to terminate CRAF development in order to save Cassini. As a result, the Cassini spacecraft became a more specialized design, canceling the implementation of the Mariner Mark II series.
The spacecraft, including the orbiter and the probe, is the largest and most complex unmanned interplanetary spacecraft built to date. The orbiter has a mass of 2,150 kg (4,740 lb), the probe 350 kg (770 lb). With the launch vehicle adapter and 3,132 kg (6,905 lb) of propellants at launch, the spacecraft had a mass of about 5,600 kg (12,300 lb) at that time. Only the two Phobos spacecraft sent to Mars by the Soviet Union were heavier up to that time.
The Cassini spacecraft is more than 6.8 meters (22 ft) high and more than 4 meters (13 ft) wide. The complexity of the spacecraft is necessitated both by its trajectory (flight path) to Saturn, and by the ambitious program of scientific observations once the spacecraft reaches its destination. Cassini has at least 1,630 interconnected electronic components, 22,000 wire connections, and over 14 kilometers (8.7 mi) of cabling. The core control computer CPU was a redundant MIL-STD-1750A control system.
Cassini is powered by 32.7 kg of plutonium-238—the heat from the material's radioactive decay is turned into electricity. Huygens was supported by Cassini during cruise, but used chemical batteries when independent.
Now that the Cassini probe is orbiting Saturn, it is between 8.2 and 10.2 astronomical units from the Earth. Because of this, it takes between 68 to 84 minutes for radio signals to travel from Earth to the spacecraft, and vice-versa. Thus, ground controllers cannot give "real-time" instructions to the spacecraft, either for day-to-day operations, or in cases of unexpected events. Even if they responded immediately after becoming aware of a problem, at least two hours will have passed between the occurrence of the problem itself and the reception of the engineers' response by the satellite.
INSTRUMENTS:
Cassini's instrumentation consists of: a synthetic aperture radar mapper, a charge-coupled device imaging system, a visible/infrared mapping spectrometer, a composite infrared spectrometer, a cosmic dust analyzer, a radio and plasma wave experiment, a plasma spectrometer, an ultraviolet imaging spectrograph, a magnetospheric imaging instrument, a magnetometer and an ion/neutral mass spectrometer. Telemetry from the communications antenna and other special transmitters (an S-band transmitter and a dual-frequency Ka-band system) will also be used to make observations of the atmospheres of Titan and Saturn and to measure the gravity fields of the planet and its satellites.
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 Cassiniorbiter is 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 will still be 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 on.)
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 fly-by was the final instance when the Cassini space 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 Cassini space 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(0.0005 per cent, i.e. a fraction 0.000005, of 1 billion cancer deaths expected anyway from other causes; the product is incorrectly calculated elsewhere as 500,000 deaths), but the odds against that happening were more than 1 million to one.