Cassini: exploring Saturn's moon
The international Cassini spacecraft has flown over the south polar region of Enceladus, a moon of Saturn covered by a liquid ocean, at only 49 kilometers from the surface. The historical approach was meant to collect all possible information from the cloud of icy particles emitted from the southern polar area of Enceladus.
Cassini is the result of a joint project involving NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI), and has been orbiting around Saturn since 2004. It was launched in October 1997 together with the ESA space probe Huygens and, once it reached Saturn, it studied its rings and magnetic field. On 25 December 2004, the Huygens probe separated from the mother ship and headed for Saturn's largest moon Titan. In January 2005, Huygens went down into Titan's atmosphere, collecting data on it in addition to images of the surface and sounds from the surrounding environment. From the observation of the moon Enceladus, scientists hope to obtain information on whether there might be hydrothermal activity on it and the impact of such activity on the ability of the moon to host simple life forms. Cassini is scheduled for one last orbit around Enceladus on December 19, when it will measure the moon's internal temperature from a distance of about 5000 km.
The Italian space industry had a prominent role in this mission thanks to Thales Alenia Space and Finmeccanica-Selex ES.
Thales Alenia Space was picked as the prime contractor for the Huygens space probe. The head of a consortium which brought together 40 companies and laboratories, it was the first in Europe to take up the technical challenge of building a space probe designed to face extreme conditions. With Cassini-Huygens, Europe undertook an unprecedented planetary program, which planned to enter the atmosphere of another planet. In order to meet the requirements, it was necessary to develop a space probe capable of sustaining a seven-year journey of more than 3 billion kilometres inside the Solar System, distant from the sun and with temperatures of minus 200 degrees Celsius.
Thales Alenia Space was responsible for designing and manufacturing the high-gain antenna (HGA/LGA) that enables all communications to and from Earth. With a diameter of four meters and a lightweight and resistant carbon fiber reflector, the antenna is a “jewel” that can operate in the extreme environmental conditions encountered during the course of the mission. Being able to withstand a range of 400 degrees Celsius, it was used as an umbrella to protect the spacecraft from 180 degrees Celsius plus heat during the flyby with Venus, the closest point to the Sun. It has been working at a temperature of minus 200 degrees since orbiting around Saturn. Thales Alenia Space also made the multimode radar which helped explain many of Titan's morphological traits. Developed in Rome in collaboration with NASA, this technology was used first in its radiometric mode on the way to Saturn, while flying close to Jupiter, allowing to obtain a very considerable scientific achievement in the study of the magnetosphere of that planet. As for the synthetic aperture radar (SAR) technology, which uses radio frequencies, it can peer through Titan's dense atmosphere, where optical sensors cannot reach.
Finmeccanica-Selex ES provided the mission with the SRU - Stellar Reference Unit sensor, in addition to the two instruments VIMS - Visible Imager Spectrometer - and HASI - Huygens Atmospheric Structure Instrument. The SRU is a sensor used to keep Cassini's balance during its interplanetary flight. This function is critical to the success of the mission because on this sensor depends the radio link with earth. The SRU is made of a complex system of lenses (telescope) which produces the image of a set of stars on its focal plane (CCD). The image is then converted into an electrical signal and digitally transferred to the onboard computer. By processing the position of the stars the orientation of the satellite is determined. VIMS/V is a visible range imaging spectrometer. It consists essentially of three parts: a sophisticated telescope made up of five mirrors, one of which rotates to make images, the actual spectrometer with a diffraction grating and a CCD, and an electronic module. The instrument outputs images of the same scene taken with 96 different “colors”, by which one can determine the components of the atmosphere and soil of the planets. HASI is an instrument with which, through the use of various sensors (accelerometers, temperature pressure and electric field sensors), it was made possible to study the vertical structure of the atmosphere while the descent module was descending on Titan. This instrument consists of sensors located in strategic points on the descent module and on a data processing box.