Rosetta takes shape in Finland
21 July 1999Deep in the Finnish countryside, the Structural and Thermal Model (STM) ofthe Rosetta orbiter is nearing completion. At the Finavitec factory in thevillage of Halli, some 250 km north of Helsinki, engineers are addingequipment panels to the spacecraft's main structure before shipment toItaly next month.
The STM - the main skeleton of the spacecraft - comprises two main sections. At its heart is a 3 metre high central cylinder which is divided into quarters by vertical shear panels. More aluminium honeycomb panels are attached to the outside of this 1.2 diameter ring to create the familiar box-shaped structure which will eventually carry the solar panels and scientific instruments.
Finavitec engineers have already successfully completed a series of static load tests on the central section. As hydraulic jacks pull on the spacecraft's panels, gauges placed in strategic locations measure the stresses being imposed on the structure.
"These tests tell us two main things," said Rosetta System Engineering Manager, Jan van Casteren. "First we want to prove that nothing will break. For example, the Rosetta lander will be directly coupled to the shear panels, so it will be shaken during launch and pull on the side of the spacecraft. These stresses can be simulated during the static load tests by pulling on the lander side of the STM with a force of 2.7 tonnes. An even bigger load - 11.3 tonnes - is applied to the lower fuel tank area of the central cylinder which will eventually be filled with oxidiser."
"We can also see if the structure behaves as expected under such loads by comparing our measurements with predictions from computer models," he added. "If they don't match, we know something is wrong."
Once the 200 kg STM structure is completed and cleaned, it will be transported to the Turin plant of Alenia Aerospazio. There, the tanks and the spacecraft equipment will be added and Structural and Thermal Models of the 12 scientific instruments and the Lander will be installed.
Rosetta is the second major ESA science project in which Finavitec has taken a significant role. The company was previous involved in making a 6 metre long telescope tube for the XMM spacecraft. These contracts were awarded after Finland became ESA's most recent member state on 1 January 1995.