Cassini–Huygens


Cassini–Huygens, commonly called Cassini, was a space-research mission by NASA, the European Space Agency, and the Italian Space Agency to send a space probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA's Cassini space probe and ESA's Huygens lander, which landed on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit, where it stayed from 2004 to 2017. The two craft took their names from the astronomers Giovanni Cassini and Christiaan Huygens.
Launched aboard a Titan IVB/Centaur on October 15, 1997, Cassini was active in space for nearly 20 years, spending almost 7 years in transit and 13 years orbiting Saturn, studying the planet and its system after entering orbit on July 1, 2004.
The voyage to Saturn included flybys of Venus, Earth, the asteroid 2685 Masursky, and Jupiter. The mission ended on September 15, 2017, when Cassinis trajectory took it into Saturn's upper atmosphere and it burned up in order to prevent any risk of contaminating Saturn's moons, which might have offered habitable environments to stowaway terrestrial microbes on the spacecraft. The mission was successful beyond expectations – NASA's Planetary Science Division Director, Jim Green, described Cassini–Huygens as a "mission of firsts" that revolutionized human understanding of the Saturn system, including its moons and rings, and our understanding of where life might be found in the Solar System.

Overview

Planning and development

Scientists and individuals from 27 countries made up the joint team responsible for designing, building, flying and collecting data from the Cassini orbiter and the Huygens probe.
Cassinis planners originally scheduled a mission of four years, from June 2004 to May 2008. The mission was extended for another two years until September 2010, branded the Cassini Equinox Mission. The mission was extended a second and final time with the Cassini Solstice Mission, lasting another seven years until September 15, 2017, on which date Cassini was de-orbited to burn up in Saturn's upper atmosphere. The Huygens module traveled with Cassini until its separation from the probe on December 25, 2004; Huygens landed by parachute on Titan on January 14, 2005. The separation was facilitated by the SED, which provided a relative separation speed of and a spin rate of 7.5 rpm. 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 Earth's Moon.
At the end of its mission, the Cassini spacecraft executed its "Grand Finale": a number of risky passes through the gaps between Saturn and its inner rings. This phase aimed to maximize Cassini scientific outcome before the spacecraft was intentionally destroyed to prevent potential contamination of Saturn's moons if Cassini were to unintentionally crash into them when maneuvering the probe was no longer possible due to power loss or other communication issues at the end of its operational lifespan. Cassini's atmospheric entry on Saturn ended the mission, but analysis of the returned data will continue for many years.

NASA and JPL

's Jet Propulsion Laboratory, where the orbiter was assembled, managed the mission. The European Space Research and Technology Centre developed Huygens. The centre's prime contractor, Aérospatiale of France, assembled the probe with equipment and instruments supplied by many European countries. The Italian Space Agency provided the Cassini orbiter's high-gain radio antenna, with the incorporation of a low-gain antenna, a compact and lightweight radar, which also used the high-gain antenna and served as a synthetic-aperture radar, a radar altimeter, a radiometer, the radio science subsystem, and the visible-channel portion VIMS-V of VIMS spectrometer.
NASA provided the VIMS infrared counterpart, as well as the Main Electronic Assembly, which included electronic sub-assemblies 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 the Cassini Equinox Mission.
It was extended again in February 2010 as the Cassini Solstice Mission.

Naming

The mission consisted of two main elements: the ASI/NASA Cassini orbiter, named for the Italian astronomer Giovanni Domenico Cassini, the discoverer of Saturn's ring divisions and four of its satellites; and the ESA-developed Huygens probe, named for the Dutch astronomer, mathematician and physicist Christiaan Huygens, discoverer of Titan.
The mission was commonly called Saturn Orbiter Titan Probe during gestation, both as a Mariner Mark II mission and generically.
Cassini–Huygens was a Flagship-class mission to the outer planets. The other planetary flagships include Galileo, Voyager, and Viking.

Objectives

Cassini had several objectives, including:
  • Determining the three-dimensional structure and dynamic behavior of the rings of Saturn.
  • Determining the composition of the satellite surfaces and the geological history of each object.
  • Determining the nature and origin of the dark material on Iapetus's leading hemisphere.
  • Measuring the three-dimensional structure and dynamic behavior of the magnetosphere.
  • Studying the dynamic behavior of Saturn's atmosphere at cloud level.
  • Studying the time variability of Titan's clouds and hazes.
  • Characterizing Titan's surface on a regional scale.
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 engines, the Centaur upper stage, and a payload enclosure, or fairing.
The total cost of this scientific exploration mission was 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, the ESA $500 million, and the ASI $160 million. However, these figures are from the press kit which was prepared in October 2000. They do not include inflation over the course of a very long mission, nor do they include the cost of the extended missions.
The primary mission for Cassini was completed on July 30, 2008. The mission was extended to June 2010. 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 6 years until 2017, ending at the time of summer solstice in Saturn's northern hemisphere. The extension enabled another 155 revolutions around the planet, 54 flybys of Titan and 11 flybys of Enceladus.
In 2017, an encounter with Titan changed its orbit in such a way that, at closest approach to Saturn, it was only above the planet's cloudtops, below the inner edge of the D ring. This sequence of "proximal orbits" ended when its final encounter with Titan sent the probe into Saturn's atmosphere to be destroyed.

Destinations

Selected destinations

History

Cassini–Huygenss origins date to 1982, when the European Science Foundation and the American National Academy of Sciences formed a working group to investigate future cooperative missions. Two European scientists suggested a paired Saturn Orbiter and Titan Probe as a possible joint mission. In 1983, NASA's Solar System Exploration Committee recommended the same Orbiter and Probe pair as a core NASA project. NASA and the European Space Agency performed a joint study of the potential mission from 1984 to 1985. ESA continued with its own study in 1986, while the American astronaut Sally Ride, in her influential 1987 report NASA Leadership and America's Future in Space, also examined and approved of the Cassini mission.
While Ride's report described the Saturn orbiter and probe as a NASA solo mission, in 1988 the Associate Administrator for Space Science and Applications of NASA, 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 the three candidates at hand and promising that NASA would commit to the mission as soon as ESA did.
At the time, NASA was becoming more sensitive to the strain that had developed between the American and European space programs as a result of European perceptions that NASA had not treated it like an equal during previous collaborations. NASA officials and advisers involved in promoting and planning Cassini–Huygens attempted to correct this trend by stressing their desire to evenly share any scientific and technology benefits resulting from the mission. In part, this newfound spirit of cooperation with Europe was driven by a sense of competition with the Soviet Union, which had begun to cooperate more closely with Europe as ESA drew further away from NASA. Late in 1988, ESA chose Cassini–Huygens as its next major mission and the following year the program received major funding in the US.
The collaboration not only improved relations between the two space programs but also helped Cassini–Huygens survive congressional budget cuts in the United States. Cassini–Huygens came under fire politically in both 1992 and 1994, but NASA successfully persuaded the United States Congress that it would be unwise to halt the project after ESA had already poured funds into development because frustration on broken space exploration promises might spill over into other areas of foreign relations. The project proceeded politically smoothly after 1994, although citizens' groups concerned about the potential environmental impact a launch failure might have attempted to derail it through protests and lawsuits until and past its 1997 launch.