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Timer from Terma to Titan
Terma Space
In 1997, the U.S. space organization NASA launched its spacecraft Cassini, heading for the planet Saturn. Thursday, 1 July 2004, seven years and three billion km later, the journey ends. This takes place when Cassini is inserted into orbit around the planet with the fascinating rings.

Tekst: Max Jørgensen
Foto: Illustration fra NASA

It also marks the beginning of the next phase, which is expected to be completed successfully in January 2005. At this point, the European part of the mission, the ESA probe Huygens, will be released from the main spacecraft to parachute through the atmosphere to the surface of Saturn's largest and most interesting moon, Titan.

The Cassini-Huygens mission to Saturn is the most ambitious effort in planetary space exploration ever mounted. For the very first time, a spacecraft is inserted into orbit around a planet so far away from Earth. And for the very first time, a probe is to land on the moon of another planet.

Timer will wake up the system
On board Huygens is a piece of advanced electronics developed by Terma. It is a timer unit, which will play an important role once the landing procedure is to be implemented.

- Once the Huygens probe separates from the Cassini orbiter, it will begin a 22-day journey to the atmosphere of Titan. During this time, no systems will be active on board the probe except for our timer. The timer is to "wake up" the other instruments when the probe reaches Titan, explains Hans Jensen, Chief Engineer in Terma Space at Lystrup in Denmark, where the timer was developed.

- For safety reasons, the probe actually carries three identical timers. Once the probe detects Titan's atmosphere, two of the sleep timers will go off, awakening the probe's science instruments and prepare for landing, tells Hans Jensen.

Three hour journey through Titans atmosphere
One of the major challenges in connection with the mission will be to calculate Huygens' exact travel time from the Cassini orbiter to Titan. 22 days is an approximate number. Once Cassini has entered into orbit around Saturn, it will be possible to calculate the exact travel time. This travel time will then be programmed into the timers, in order for them to go off at the right time.

Huygens will enter the atmosphere of Titan at a speed of approx. 20,000 km/h, which will develop extreme temperatures due to friction. Thus, Huygens is built like a shellfish: a hard shell to protect a delicate interior from these extreme temperatures. The probe will use three different parachutes in sequence during the descent to slow down the probe. On its way to the surface of the moon, the instruments on board will measure the atmospheric conditions, while a camera on board will take approx. 1,000 images prior to landing.

- This phase is the most important phase of the entire expedition. Huygens' journey through the atmosphere will last approx. three hours. Within that period of time, it is to collect as much data as possible and transmit the data to Cassini, which will later transmit the data down to us on Earth, explains Hans Jensen.

Conditions similar to those on Earth when life began
The further destiny of Huygens is yet unknown. Scientists know very little about the surface of Titan and the surroundings in which the probe will land. It may land on a solid surface, but it may also land in a lake of liquid gases. Thus, the probe is constructed to float. If Huygens survives its meeting with Titan, scientists obtain an extra bonus. Huygens has the capacity to collect and transmit data for approx. half an hour before the last power from the batteries are used.

Titan is interesting as scientists assume that the conditions in certain areas are similar to those on Earth at the time when life began. By studying the chemical conditions on Titan, we can add new knowledge to the mystery of how life began on Earth. Thus, the Cassini mission is a very important milestone in the history of space explorations.

Huygens og Cassini
The Cassini-Huygens mission is named after two European astronomers from the 17th century. The Dutch astronomer Christiaan Huygens (1629-1695) discovered Saturn's rings and Titan. A few years later the French-Italian Astronomer Jean-Dominique Cassini (1625-1712) discovered Saturn's four other major moons - Iapetus, Rhea, Tethys, and Dione. He also discovered that Saturn's rings are split largely into two parts by a narrow gap, known since as the 'Cassini Division'.